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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2018-04-03 22:35:51 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-04-03 22:35:51 +0200 |
| commit | bb2407a7219760926760f0448fddf00d625e5aec (patch) | |
| tree | 68d2b7a17f0bb837d04d658a56baf16dd261210f /Documentation/trace | |
| parent | Merge tag 'leds_for_4.17-rc1' of git://git.kernel.org/pub/scm/linux/kernel/gi... (diff) | |
| parent | Documentation/process: update FUSE project website (diff) | |
| download | linux-bb2407a7219760926760f0448fddf00d625e5aec.tar.xz linux-bb2407a7219760926760f0448fddf00d625e5aec.zip | |
Merge tag 'docs-4.17' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"There's been a fair amount of activity in Documentation/ this time
around:
- Lots of work aligning Documentation/ABI with reality, done by
Aishwarya Pant.
- The trace documentation has been converted to RST by Changbin Du
- I thrashed up kernel-doc to deal with a parsing issue and to try to
make the code more readable. It's still a 20+-year-old Perl hack,
though.
- Lots of other updates, typo fixes, and more"
* tag 'docs-4.17' of git://git.lwn.net/linux: (82 commits)
Documentation/process: update FUSE project website
docs: kernel-doc: fix parsing of arrays
dmaengine: Fix spelling for parenthesis in dmatest documentation
dmaengine: Make dmatest.rst indeed reST compatible
dmaengine: Add note to dmatest documentation about supported channels
Documentation: magic-numbers: Fix typo
Documentation: admin-guide: add kvmconfig, xenconfig and tinyconfig commands
Input: alps - Update documentation for trackstick v3 format
Documentation: Mention why %p prints ptrval
COPYING: use the new text with points to the license files
COPYING: create a new file with points to the Kernel license files
Input: trackpoint: document sysfs interface
xfs: Change URL for the project in xfs.txt
char/bsr: add sysfs interface documentation
acpi: nfit: document sysfs interface
block: rbd: update sysfs interface
Documentation/sparse: fix typo
Documentation/CodingStyle: Add an example for braces
docs/vm: update 00-INDEX
kernel-doc: Remove __sched markings
...
Diffstat (limited to 'Documentation/trace')
| -rw-r--r-- | Documentation/trace/events-kmem.rst (renamed from Documentation/trace/events-kmem.txt) | 50 | ||||
| -rw-r--r-- | Documentation/trace/events-msr.rst | 40 | ||||
| -rw-r--r-- | Documentation/trace/events-msr.txt | 37 | ||||
| -rw-r--r-- | Documentation/trace/events-nmi.rst | 45 | ||||
| -rw-r--r-- | Documentation/trace/events-nmi.txt | 43 | ||||
| -rw-r--r-- | Documentation/trace/events-power.rst (renamed from Documentation/trace/events-power.txt) | 52 | ||||
| -rw-r--r-- | Documentation/trace/events.rst (renamed from Documentation/trace/events.txt) | 677 | ||||
| -rw-r--r-- | Documentation/trace/ftrace-design.rst (renamed from Documentation/trace/ftrace-design.txt) | 252 | ||||
| -rw-r--r-- | Documentation/trace/ftrace-uses.rst | 23 | ||||
| -rw-r--r-- | Documentation/trace/ftrace.rst | 3332 | ||||
| -rw-r--r-- | Documentation/trace/ftrace.txt | 3220 | ||||
| -rw-r--r-- | Documentation/trace/hwlat_detector.rst (renamed from Documentation/trace/hwlat_detector.txt) | 26 | ||||
| -rw-r--r-- | Documentation/trace/index.rst | 23 | ||||
| -rw-r--r-- | Documentation/trace/intel_th.rst (renamed from Documentation/trace/intel_th.txt) | 43 | ||||
| -rw-r--r-- | Documentation/trace/kprobetrace.rst (renamed from Documentation/trace/kprobetrace.txt) | 100 | ||||
| -rw-r--r-- | Documentation/trace/mmiotrace.rst (renamed from Documentation/trace/mmiotrace.txt) | 86 | ||||
| -rw-r--r-- | Documentation/trace/stm.rst (renamed from Documentation/trace/stm.txt) | 23 | ||||
| -rw-r--r-- | Documentation/trace/tracepoint-analysis.rst (renamed from Documentation/trace/tracepoint-analysis.txt) | 41 | ||||
| -rw-r--r-- | Documentation/trace/tracepoints.rst (renamed from Documentation/trace/tracepoints.txt) | 77 | ||||
| -rw-r--r-- | Documentation/trace/uprobetracer.rst (renamed from Documentation/trace/uprobetracer.txt) | 44 |
20 files changed, 4240 insertions, 3994 deletions
diff --git a/Documentation/trace/events-kmem.txt b/Documentation/trace/events-kmem.rst index 194800410061..555484110e36 100644 --- a/Documentation/trace/events-kmem.txt +++ b/Documentation/trace/events-kmem.rst @@ -1,22 +1,26 @@ - Subsystem Trace Points: kmem +============================ +Subsystem Trace Points: kmem +============================ The kmem tracing system captures events related to object and page allocation within the kernel. Broadly speaking there are five major subheadings. - o Slab allocation of small objects of unknown type (kmalloc) - o Slab allocation of small objects of known type - o Page allocation - o Per-CPU Allocator Activity - o External Fragmentation + - Slab allocation of small objects of unknown type (kmalloc) + - Slab allocation of small objects of known type + - Page allocation + - Per-CPU Allocator Activity + - External Fragmentation This document describes what each of the tracepoints is and why they might be useful. 1. Slab allocation of small objects of unknown type =================================================== -kmalloc call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s -kmalloc_node call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d -kfree call_site=%lx ptr=%p +:: + + kmalloc call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s + kmalloc_node call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d + kfree call_site=%lx ptr=%p Heavy activity for these events may indicate that a specific cache is justified, particularly if kmalloc slab pages are getting significantly @@ -27,9 +31,11 @@ the allocation sites were. 2. Slab allocation of small objects of known type ================================================= -kmem_cache_alloc call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s -kmem_cache_alloc_node call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d -kmem_cache_free call_site=%lx ptr=%p +:: + + kmem_cache_alloc call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s + kmem_cache_alloc_node call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d + kmem_cache_free call_site=%lx ptr=%p These events are similar in usage to the kmalloc-related events except that it is likely easier to pin the event down to a specific cache. At the time @@ -38,10 +44,12 @@ but the call_site can usually be used to extrapolate that information. 3. Page allocation ================== -mm_page_alloc page=%p pfn=%lu order=%d migratetype=%d gfp_flags=%s -mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d -mm_page_free page=%p pfn=%lu order=%d -mm_page_free_batched page=%p pfn=%lu order=%d cold=%d +:: + + mm_page_alloc page=%p pfn=%lu order=%d migratetype=%d gfp_flags=%s + mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d + mm_page_free page=%p pfn=%lu order=%d + mm_page_free_batched page=%p pfn=%lu order=%d cold=%d These four events deal with page allocation and freeing. mm_page_alloc is a simple indicator of page allocator activity. Pages may be allocated from @@ -65,8 +73,10 @@ contention on the zone->lru_lock. 4. Per-CPU Allocator Activity ============================= -mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d -mm_page_pcpu_drain page=%p pfn=%lu order=%d cpu=%d migratetype=%d +:: + + mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d + mm_page_pcpu_drain page=%p pfn=%lu order=%d cpu=%d migratetype=%d In front of the page allocator is a per-cpu page allocator. It exists only for order-0 pages, reduces contention on the zone->lock and reduces the @@ -92,7 +102,9 @@ can be allocated and freed on the same CPU through some algorithm change. 5. External Fragmentation ========================= -mm_page_alloc_extfrag page=%p pfn=%lu alloc_order=%d fallback_order=%d pageblock_order=%d alloc_migratetype=%d fallback_migratetype=%d fragmenting=%d change_ownership=%d +:: + + mm_page_alloc_extfrag page=%p pfn=%lu alloc_order=%d fallback_order=%d pageblock_order=%d alloc_migratetype=%d fallback_migratetype=%d fragmenting=%d change_ownership=%d External fragmentation affects whether a high-order allocation will be successful or not. For some types of hardware, this is important although diff --git a/Documentation/trace/events-msr.rst b/Documentation/trace/events-msr.rst new file mode 100644 index 000000000000..e938aa0b6f4f --- /dev/null +++ b/Documentation/trace/events-msr.rst @@ -0,0 +1,40 @@ +================ +MSR Trace Events +================ + +The x86 kernel supports tracing most MSR (Model Specific Register) accesses. +To see the definition of the MSRs on Intel systems please see the SDM +at http://www.intel.com/sdm (Volume 3) + +Available trace points: + +/sys/kernel/debug/tracing/events/msr/ + +Trace MSR reads: + +read_msr + + - msr: MSR number + - val: Value written + - failed: 1 if the access failed, otherwise 0 + + +Trace MSR writes: + +write_msr + + - msr: MSR number + - val: Value written + - failed: 1 if the access failed, otherwise 0 + + +Trace RDPMC in kernel: + +rdpmc + +The trace data can be post processed with the postprocess/decode_msr.py script:: + + cat /sys/kernel/debug/tracing/trace | decode_msr.py /usr/src/linux/include/asm/msr-index.h + +to add symbolic MSR names. + diff --git a/Documentation/trace/events-msr.txt b/Documentation/trace/events-msr.txt deleted file mode 100644 index 78c383bf06aa..000000000000 --- a/Documentation/trace/events-msr.txt +++ /dev/null @@ -1,37 +0,0 @@ - -The x86 kernel supports tracing most MSR (Model Specific Register) accesses. -To see the definition of the MSRs on Intel systems please see the SDM -at http://www.intel.com/sdm (Volume 3) - -Available trace points: - -/sys/kernel/debug/tracing/events/msr/ - -Trace MSR reads - -read_msr - -msr: MSR number -val: Value written -failed: 1 if the access failed, otherwise 0 - - -Trace MSR writes - -write_msr - -msr: MSR number -val: Value written -failed: 1 if the access failed, otherwise 0 - - -Trace RDPMC in kernel - -rdpmc - -The trace data can be post processed with the postprocess/decode_msr.py script - -cat /sys/kernel/debug/tracing/trace | decode_msr.py /usr/src/linux/include/asm/msr-index.h - -to add symbolic MSR names. - diff --git a/Documentation/trace/events-nmi.rst b/Documentation/trace/events-nmi.rst new file mode 100644 index 000000000000..9e0a7289d80a --- /dev/null +++ b/Documentation/trace/events-nmi.rst @@ -0,0 +1,45 @@ +================ +NMI Trace Events +================ + +These events normally show up here: + + /sys/kernel/debug/tracing/events/nmi + + +nmi_handler +----------- + +You might want to use this tracepoint if you suspect that your +NMI handlers are hogging large amounts of CPU time. The kernel +will warn if it sees long-running handlers:: + + INFO: NMI handler took too long to run: 9.207 msecs + +and this tracepoint will allow you to drill down and get some +more details. + +Let's say you suspect that perf_event_nmi_handler() is causing +you some problems and you only want to trace that handler +specifically. You need to find its address:: + + $ grep perf_event_nmi_handler /proc/kallsyms + ffffffff81625600 t perf_event_nmi_handler + +Let's also say you are only interested in when that function is +really hogging a lot of CPU time, like a millisecond at a time. +Note that the kernel's output is in milliseconds, but the input +to the filter is in nanoseconds! You can filter on 'delta_ns':: + + cd /sys/kernel/debug/tracing/events/nmi/nmi_handler + echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter + echo 1 > enable + +Your output would then look like:: + + $ cat /sys/kernel/debug/tracing/trace_pipe + <idle>-0 [000] d.h3 505.397558: nmi_handler: perf_event_nmi_handler() delta_ns: 3236765 handled: 1 + <idle>-0 [000] d.h3 505.805893: nmi_handler: perf_event_nmi_handler() delta_ns: 3174234 handled: 1 + <idle>-0 [000] d.h3 506.158206: nmi_handler: perf_event_nmi_handler() delta_ns: 3084642 handled: 1 + <idle>-0 [000] d.h3 506.334346: nmi_handler: perf_event_nmi_handler() delta_ns: 3080351 handled: 1 + diff --git a/Documentation/trace/events-nmi.txt b/Documentation/trace/events-nmi.txt deleted file mode 100644 index c03c8c89f08d..000000000000 --- a/Documentation/trace/events-nmi.txt +++ /dev/null @@ -1,43 +0,0 @@ -NMI Trace Events - -These events normally show up here: - - /sys/kernel/debug/tracing/events/nmi - --- - -nmi_handler: - -You might want to use this tracepoint if you suspect that your -NMI handlers are hogging large amounts of CPU time. The kernel -will warn if it sees long-running handlers: - - INFO: NMI handler took too long to run: 9.207 msecs - -and this tracepoint will allow you to drill down and get some -more details. - -Let's say you suspect that perf_event_nmi_handler() is causing -you some problems and you only want to trace that handler -specifically. You need to find its address: - - $ grep perf_event_nmi_handler /proc/kallsyms - ffffffff81625600 t perf_event_nmi_handler - -Let's also say you are only interested in when that function is -really hogging a lot of CPU time, like a millisecond at a time. -Note that the kernel's output is in milliseconds, but the input -to the filter is in nanoseconds! You can filter on 'delta_ns': - -cd /sys/kernel/debug/tracing/events/nmi/nmi_handler -echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter -echo 1 > enable - -Your output would then look like: - -$ cat /sys/kernel/debug/tracing/trace_pipe -<idle>-0 [000] d.h3 505.397558: nmi_handler: perf_event_nmi_handler() delta_ns: 3236765 handled: 1 -<idle>-0 [000] d.h3 505.805893: nmi_handler: perf_event_nmi_handler() delta_ns: 3174234 handled: 1 -<idle>-0 [000] d.h3 506.158206: nmi_handler: perf_event_nmi_handler() delta_ns: 3084642 handled: 1 -<idle>-0 [000] d.h3 506.334346: nmi_handler: perf_event_nmi_handler() delta_ns: 3080351 handled: 1 - diff --git a/Documentation/trace/events-power.txt b/Documentation/trace/events-power.rst index 21d514ced212..a77daca75e30 100644 --- a/Documentation/trace/events-power.txt +++ b/Documentation/trace/events-power.rst @@ -1,13 +1,14 @@ - - Subsystem Trace Points: power +============================= +Subsystem Trace Points: power +============================= The power tracing system captures events related to power transitions within the kernel. Broadly speaking there are three major subheadings: - o Power state switch which reports events related to suspend (S-states), - cpuidle (C-states) and cpufreq (P-states) - o System clock related changes - o Power domains related changes and transitions + - Power state switch which reports events related to suspend (S-states), + cpuidle (C-states) and cpufreq (P-states) + - System clock related changes + - Power domains related changes and transitions This document describes what each of the tracepoints is and why they might be useful. @@ -22,14 +23,16 @@ Cf. include/trace/events/power.h for the events definitions. A 'cpu' event class gathers the CPU-related events: cpuidle and cpufreq. +:: -cpu_idle "state=%lu cpu_id=%lu" -cpu_frequency "state=%lu cpu_id=%lu" + cpu_idle "state=%lu cpu_id=%lu" + cpu_frequency "state=%lu cpu_id=%lu" A suspend event is used to indicate the system going in and out of the suspend mode: +:: -machine_suspend "state=%lu" + machine_suspend "state=%lu" Note: the value of '-1' or '4294967295' for state means an exit from the current state, @@ -45,10 +48,11 @@ correctly draw the states diagrams and to calculate accurate statistics etc. ================ The clock events are used for clock enable/disable and for clock rate change. +:: -clock_enable "%s state=%lu cpu_id=%lu" -clock_disable "%s state=%lu cpu_id=%lu" -clock_set_rate "%s state=%lu cpu_id=%lu" + clock_enable "%s state=%lu cpu_id=%lu" + clock_disable "%s state=%lu cpu_id=%lu" + clock_set_rate "%s state=%lu cpu_id=%lu" The first parameter gives the clock name (e.g. "gpio1_iclk"). The second parameter is '1' for enable, '0' for disable, the target @@ -57,8 +61,9 @@ clock rate for set_rate. 3. Power domains events ======================= The power domain events are used for power domains transitions +:: -power_domain_target "%s state=%lu cpu_id=%lu" + power_domain_target "%s state=%lu cpu_id=%lu" The first parameter gives the power domain name (e.g. "mpu_pwrdm"). The second parameter is the power domain target state. @@ -67,28 +72,31 @@ The second parameter is the power domain target state. ================ The PM QoS events are used for QoS add/update/remove request and for target/flags update. +:: -pm_qos_add_request "pm_qos_class=%s value=%d" -pm_qos_update_request "pm_qos_class=%s value=%d" -pm_qos_remove_request "pm_qos_class=%s value=%d" -pm_qos_update_request_timeout "pm_qos_class=%s value=%d, timeout_us=%ld" + pm_qos_add_request "pm_qos_class=%s value=%d" + pm_qos_update_request "pm_qos_class=%s value=%d" + pm_qos_remove_request "pm_qos_class=%s value=%d" + pm_qos_update_request_timeout "pm_qos_class=%s value=%d, timeout_us=%ld" The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY"). The second parameter is value to be added/updated/removed. The third parameter is timeout value in usec. +:: -pm_qos_update_target "action=%s prev_value=%d curr_value=%d" -pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x" + pm_qos_update_target "action=%s prev_value=%d curr_value=%d" + pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x" The first parameter gives the QoS action name (e.g. "ADD_REQ"). The second parameter is the previous QoS value. The third parameter is the current QoS value to update. And, there are also events used for device PM QoS add/update/remove request. +:: -dev_pm_qos_add_request "device=%s type=%s new_value=%d" -dev_pm_qos_update_request "device=%s type=%s new_value=%d" -dev_pm_qos_remove_request "device=%s type=%s new_value=%d" + dev_pm_qos_add_request "device=%s type=%s new_value=%d" + dev_pm_qos_update_request "device=%s type=%s new_value=%d" + dev_pm_qos_remove_request "device=%s type=%s new_value=%d" The first parameter gives the device name which tries to add/update/remove QoS requests. diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.rst index 2cc08d4a326e..bdf1963ba6ba 100644 --- a/Documentation/trace/events.txt +++ b/Documentation/trace/events.rst @@ -1,7 +1,9 @@ - Event Tracing +============= +Event Tracing +============= - Documentation written by Theodore Ts'o - Updated by Li Zefan and Tom Zanussi +:Author: Theodore Ts'o +:Updated: Li Zefan and Tom Zanussi 1. Introduction =============== @@ -25,23 +27,22 @@ The events which are available for tracing can be found in the file /sys/kernel/debug/tracing/available_events. To enable a particular event, such as 'sched_wakeup', simply echo it -to /sys/kernel/debug/tracing/set_event. For example: +to /sys/kernel/debug/tracing/set_event. For example:: # echo sched_wakeup >> /sys/kernel/debug/tracing/set_event -[ Note: '>>' is necessary, otherwise it will firstly disable - all the events. ] +.. Note:: '>>' is necessary, otherwise it will firstly disable all the events. To disable an event, echo the event name to the set_event file prefixed -with an exclamation point: +with an exclamation point:: # echo '!sched_wakeup' >> /sys/kernel/debug/tracing/set_event -To disable all events, echo an empty line to the set_event file: +To disable all events, echo an empty line to the set_event file:: # echo > /sys/kernel/debug/tracing/set_event -To enable all events, echo '*:*' or '*:' to the set_event file: +To enable all events, echo ``*:*`` or ``*:`` to the set_event file:: # echo *:* > /sys/kernel/debug/tracing/set_event @@ -49,8 +50,8 @@ The events are organized into subsystems, such as ext4, irq, sched, etc., and a full event name looks like this: <subsystem>:<event>. The subsystem name is optional, but it is displayed in the available_events file. All of the events in a subsystem can be specified via the syntax -"<subsystem>:*"; for example, to enable all irq events, you can use the -command: +``<subsystem>:*``; for example, to enable all irq events, you can use the +command:: # echo 'irq:*' > /sys/kernel/debug/tracing/set_event @@ -60,33 +61,33 @@ command: The events available are also listed in /sys/kernel/debug/tracing/events/ hierarchy of directories. -To enable event 'sched_wakeup': +To enable event 'sched_wakeup':: # echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable -To disable it: +To disable it:: # echo 0 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable -To enable all events in sched subsystem: +To enable all events in sched subsystem:: # echo 1 > /sys/kernel/debug/tracing/events/sched/enable -To enable all events: +To enable all events:: # echo 1 > /sys/kernel/debug/tracing/events/enable When reading one of these enable files, there are four results: - 0 - all events this file affects are disabled - 1 - all events this file affects are enabled - X - there is a mixture of events enabled and disabled - ? - this file does not affect any event + - 0 - all events this file affects are disabled + - 1 - all events this file affects are enabled + - X - there is a mixture of events enabled and disabled + - ? - this file does not affect any event 2.3 Boot option --------------- -In order to facilitate early boot debugging, use boot option: +In order to facilitate early boot debugging, use boot option:: trace_event=[event-list] @@ -110,12 +111,12 @@ It also displays the format string that will be used to print the event in text mode, along with the event name and ID used for profiling. -Every event has a set of 'common' fields associated with it; these are -the fields prefixed with 'common_'. The other fields vary between +Every event has a set of ``common`` fields associated with it; these are +the fields prefixed with ``common_``. The other fields vary between events and correspond to the fields defined in the TRACE_EVENT definition for that event. -Each field in the format has the form: +Each field in the format has the form:: field:field-type field-name; offset:N; size:N; @@ -123,27 +124,27 @@ where offset is the offset of the field in the trace record and size is the size of the data item, in bytes. For example, here's the information displayed for the 'sched_wakeup' -event: +event:: -# cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/format + # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/format -name: sched_wakeup -ID: 60 -format: - field:unsigned short common_type; offset:0; size:2; - field:unsigned char common_flags; offset:2; size:1; - field:unsigned char common_preempt_count; offset:3; size:1; - field:int common_pid; offset:4; size:4; - field:int common_tgid; offset:8; size:4; + name: sched_wakeup + ID: 60 + format: + field:unsigned short common_type; offset:0; size:2; + field:unsigned char common_flags; offset:2; size:1; + field:unsigned char common_preempt_count; offset:3; size:1; + field:int common_pid; offset:4; size:4; + field:int common_tgid; offset:8; size:4; - field:char comm[TASK_COMM_LEN]; offset:12; size:16; - field:pid_t pid; offset:28; size:4; - field:int prio; offset:32; size:4; - field:int success; offset:36; size:4; - field:int cpu; offset:40; size:4; + field:char comm[TASK_COMM_LEN]; offset:12; size:16; + field:pid_t pid; offset:28; size:4; + field:int prio; offset:32; size:4; + field:int success; offset:36; size:4; + field:int cpu; offset:40; size:4; -print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid, - REC->prio, REC->success, REC->cpu + print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid, + REC->prio, REC->success, REC->cpu This event contains 10 fields, the first 5 common and the remaining 5 event-specific. All the fields for this event are numeric, except for @@ -168,7 +169,7 @@ A filter expression consists of one or more 'predicates' that can be combined using the logical operators '&&' and '||'. A predicate is simply a clause that compares the value of a field contained within a logged event with a constant value and returns either 0 or 1 depending -on whether the field value matched (1) or didn't match (0): +on whether the field value matched (1) or didn't match (0):: field-name relational-operator value @@ -189,8 +190,8 @@ And for string fields they are: ==, !=, ~ -The glob (~) accepts a wild card character (*,?) and character classes -([). For example: +The glob (~) accepts a wild card character (\*,?) and character classes +([). For example:: prev_comm ~ "*sh" prev_comm ~ "sh*" @@ -203,27 +204,27 @@ The glob (~) accepts a wild card character (*,?) and character classes A filter for an individual event is set by writing a filter expression to the 'filter' file for the given event. -For example: +For example:: -# cd /sys/kernel/debug/tracing/events/sched/sched_wakeup -# echo "common_preempt_count > 4" > filter + # cd /sys/kernel/debug/tracing/events/sched/sched_wakeup + # echo "common_preempt_count > 4" > filter -A slightly more involved example: +A slightly more involved example:: -# cd /sys/kernel/debug/tracing/events/signal/signal_generate -# echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter + # cd /sys/kernel/debug/tracing/events/signal/signal_generate + # echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter If there is an error in the expression, you'll get an 'Invalid argument' error when setting it, and the erroneous string along with -an error message can be seen by looking at the filter e.g.: +an error message can be seen by looking at the filter e.g.:: -# cd /sys/kernel/debug/tracing/events/signal/signal_generate -# echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter --bash: echo: write error: Invalid argument -# cat filter -((sig >= 10 && sig < 15) || dsig == 17) && comm != bash -^ -parse_error: Field not found + # cd /sys/kernel/debug/tracing/events/signal/signal_generate + # echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter + -bash: echo: write error: Invalid argument + # cat filter + ((sig >= 10 && sig < 15) || dsig == 17) && comm != bash + ^ + parse_error: Field not found Currently the caret ('^') for an error always appears at the beginning of the filter string; the error message should still be useful though @@ -255,35 +256,35 @@ fields can be guaranteed to propagate successfully to all events. Here are a few subsystem filter examples that also illustrate the above points: -Clear the filters on all events in the sched subsystem: +Clear the filters on all events in the sched subsystem:: -# cd /sys/kernel/debug/tracing/events/sched -# echo 0 > filter -# cat sched_switch/filter -none -# cat sched_wakeup/filter -none + # cd /sys/kernel/debug/tracing/events/sched + # echo 0 > filter + # cat sched_switch/filter + none + # cat sched_wakeup/filter + none Set a filter using only common fields for all events in the sched -subsystem (all events end up with the same filter): +subsystem (all events end up with the same filter):: -# cd /sys/kernel/debug/tracing/events/sched -# echo common_pid == 0 > filter -# cat sched_switch/filter -common_pid == 0 -# cat sched_wakeup/filter -common_pid == 0 + # cd /sys/kernel/debug/tracing/events/sched + # echo common_pid == 0 > filter + # cat sched_switch/filter + common_pid == 0 + # cat sched_wakeup/filter + common_pid == 0 Attempt to set a filter using a non-common field for all events in the sched subsystem (all events but those that have a prev_pid field retain -their old filters): +their old filters):: -# cd /sys/kernel/debug/tracing/events/sched -# echo prev_pid == 0 > filter -# cat sched_switch/filter -prev_pid == 0 -# cat sched_wakeup/filter -common_pid == 0 + # cd /sys/kernel/debug/tracing/events/sched + # echo prev_pid == 0 > filter + # cat sched_switch/filter + prev_pid == 0 + # cat sched_wakeup/filter + common_pid == 0 5.4 PID filtering ----------------- @@ -291,16 +292,18 @@ common_pid == 0 The set_event_pid file in the same directory as the top events directory exists, will filter all events from tracing any task that does not have the PID listed in the set_event_pid file. +:: -# cd /sys/kernel/debug/tracing -# echo $$ > set_event_pid -# echo 1 > events/enabled + # cd /sys/kernel/debug/tracing + # echo $$ > set_event_pid + # echo 1 > events/enable Will only trace events for the current task. To add more PIDs without losing the PIDs already included, use '>>'. +:: -# echo 123 244 1 >> set_event_pid + # echo 123 244 1 >> set_event_pid 6. Event triggers @@ -342,12 +345,12 @@ way, so beware about making generalizations between the two. 6.1 Expression syntax --------------------- -Triggers are added by echoing the command to the 'trigger' file: +Triggers are added by echoing the command to the 'trigger' file:: # echo 'command[:count] [if filter]' > trigger Triggers are removed by echoing the same command but starting with '!' -to the 'trigger' file: +to the 'trigger' file:: # echo '!command[:count] [if filter]' > trigger @@ -379,30 +382,30 @@ The following commands are supported: For example, the following trigger causes kmalloc events to be traced when a read system call is entered, and the :1 at the end - specifies that this enablement happens only once: + specifies that this enablement happens only once:: - # echo 'enable_event:kmem:kmalloc:1' > \ - /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger + # echo 'enable_event:kmem:kmalloc:1' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger The following trigger causes kmalloc events to stop being traced when a read system call exits. This disablement happens on every - read system call exit: + read system call exit:: - # echo 'disable_event:kmem:kmalloc' > \ - /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger + # echo 'disable_event:kmem:kmalloc' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger - The format is: + The format is:: enable_event:<system>:<event>[:count] disable_event:<system>:<event>[:count] - To remove the above commands: + To remove the above commands:: - # echo '!enable_event:kmem:kmalloc:1' > \ - /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger + # echo '!enable_event:kmem:kmalloc:1' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger - # echo '!disable_event:kmem:kmalloc' > \ - /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger + # echo '!disable_event:kmem:kmalloc' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger Note that there can be any number of enable/disable_event triggers per triggering event, but there can only be one trigger per @@ -418,34 +421,34 @@ The following commands are supported: triggering event occurs. For example, the following trigger dumps a stacktrace every time the - kmalloc tracepoint is hit: + kmalloc tracepoint is hit:: - # echo 'stacktrace' > \ - /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + # echo 'stacktrace' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger The following trigger dumps a stacktrace the first 5 times a kmalloc - request happens with a size >= 64K + request happens with a size >= 64K:: - # echo 'stacktrace:5 if bytes_req >= 65536' > \ - /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + # echo 'stacktrace:5 if bytes_req >= 65536' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger - The format is: + The format is:: stacktrace[:count] - To remove the above commands: + To remove the above commands:: - # echo '!stacktrace' > \ - /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + # echo '!stacktrace' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger - # echo '!stacktrace:5 if bytes_req >= 65536' > \ - /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + # echo '!stacktrace:5 if bytes_req >= 65536' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger The latter can also be removed more simply by the following (without - the filter): + the filter):: - # echo '!stacktrace:5' > \ - /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + # echo '!stacktrace:5' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger Note that there can be only one stacktrace trigger per triggering event. @@ -458,23 +461,23 @@ The following commands are supported: The following command creates a snapshot every time a block request queue is unplugged with a depth > 1. If you were tracing a set of events or functions at the time, the snapshot trace buffer would - capture those events when the trigger event occurred: + capture those events when the trigger event occurred:: - # echo 'snapshot if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo 'snapshot if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger - To only snapshot once: + To only snapshot once:: - # echo 'snapshot:1 if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo 'snapshot:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger - To remove the above commands: + To remove the above commands:: - # echo '!snapshot if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo '!snapshot if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger - # echo '!snapshot:1 if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo '!snapshot:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger Note that there can be only one snapshot trigger per triggering event. @@ -489,23 +492,23 @@ The following commands are supported: request queue is unplugged with a depth > 1. If you were tracing a set of events or functions at the time, you could then examine the trace buffer to see the sequence of events that led up to the - trigger event: + trigger event:: - # echo 'traceoff:1 if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo 'traceoff:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger - To always disable tracing when nr_rq > 1 : + To always disable tracing when nr_rq > 1:: - # echo 'traceoff if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo 'traceoff if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger - To remove the above commands: + To remove the above commands:: - # echo '!traceoff:1 if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo '!traceoff:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger - # echo '!traceoff if nr_rq > 1' > \ - /sys/kernel/debug/tracing/events/block/block_unplug/trigger + # echo '!traceoff if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger Note that there can be only one traceon or traceoff trigger per triggering event. @@ -517,7 +520,7 @@ The following commands are supported: totals derived from one or more trace event format fields and/or event counts (hitcount). - The format of a hist trigger is as follows: + The format of a hist trigger is as follows:: hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>] [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue] @@ -566,11 +569,11 @@ The following commands are supported: modified by appending any of the following modifiers to the field name: - .hex display a number as a hex value - .sym display an address as a symbol - .sym-offset display an address as a symbol and offset - .syscall display a syscall id as a system call name - .execname display a common_pid as a program name + - .hex display a number as a hex value + - .sym display an address as a symbol + - .sym-offset display an address as a symbol and offset + - .syscall display a syscall id as a system call name + - .execname display a common_pid as a program name Note that in general the semantics of a given field aren't interpreted when applying a modifier to it, but there are some @@ -588,15 +591,15 @@ The following commands are supported: pid-specific comm fields in the event itself. A typical usage scenario would be the following to enable a hist - trigger, read its current contents, and then turn it off: + trigger, read its current contents, and then turn it off:: - # echo 'hist:keys=skbaddr.hex:vals=len' > \ - /sys/kernel/debug/tracing/events/net/netif_rx/trigger + # echo 'hist:keys=skbaddr.hex:vals=len' > \ + /sys/kernel/debug/tracing/events/net/netif_rx/trigger - # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist + # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist - # echo '!hist:keys=skbaddr.hex:vals=len' > \ - /sys/kernel/debug/tracing/events/net/netif_rx/trigger + # echo '!hist:keys=skbaddr.hex:vals=len' > \ + /sys/kernel/debug/tracing/events/net/netif_rx/trigger The trigger file itself can be read to show the details of the currently attached hist trigger. This information is also displayed @@ -636,7 +639,7 @@ The following commands are supported: can be attached to a given event, allowing that event to kick off and stop aggregations on a host of other events. - The format is very similar to the enable/disable_event triggers: + The format is very similar to the enable/disable_event triggers:: enable_hist:<system>:<event>[:count] disable_hist:<system>:<event>[:count] @@ -649,16 +652,16 @@ The following commands are supported: A typical usage scenario for the enable_hist/disable_hist triggers would be to first set up a paused hist trigger on some event, followed by an enable_hist/disable_hist pair that turns the hist - aggregation on and off when conditions of interest are hit: + aggregation on and off when conditions of interest are hit:: - # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \ - /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger - # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \ - /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger + # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger - # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \ - /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger + # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger The above sets up an initially paused hist trigger which is unpaused and starts aggregating events when a given program is executed, and @@ -674,7 +677,7 @@ The following commands are supported: The first set of examples creates aggregations using the kmalloc event. The fields that can be used for the hist trigger are listed - in the kmalloc event's format file: + in the kmalloc event's format file:: # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format name: kmalloc @@ -693,7 +696,7 @@ The following commands are supported: We'll start by creating a hist trigger that generates a simple table that lists the total number of bytes requested for each function in - the kernel that made one or more calls to kmalloc: + the kernel that made one or more calls to kmalloc:: # echo 'hist:key=call_site:val=bytes_req' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -708,7 +711,7 @@ The following commands are supported: We'll let it run for awhile and then dump the contents of the 'hist' file in the kmalloc event's subdirectory (for readability, a number - of entries have been omitted): + of entries have been omitted):: # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active] @@ -748,7 +751,7 @@ The following commands are supported: specified in the trigger, followed by the value(s) also specified in the trigger. At the beginning of the output is a line that displays the trigger info, which can also be displayed by reading the - 'trigger' file: + 'trigger' file:: # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active] @@ -778,7 +781,7 @@ The following commands are supported: frequencies. To turn the hist trigger off, simply call up the trigger in the - command history and re-execute it with a '!' prepended: + command history and re-execute it with a '!' prepended:: # echo '!hist:key=call_site:val=bytes_req' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -786,7 +789,7 @@ The following commands are supported: Finally, notice that the call_site as displayed in the output above isn't really very useful. It's an address, but normally addresses are displayed in hex. To have a numeric field displayed as a hex - value, simply append '.hex' to the field name in the trigger: + value, simply append '.hex' to the field name in the trigger:: # echo 'hist:key=call_site.hex:val=bytes_req' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -831,7 +834,7 @@ The following commands are supported: when looking at text addresses are the corresponding symbols instead. To have an address displayed as symbolic value instead, simply append '.sym' or '.sym-offset' to the field name in the - trigger: + trigger:: # echo 'hist:key=call_site.sym:val=bytes_req' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -881,7 +884,7 @@ The following commands are supported: run. If instead we we wanted to see the top kmalloc callers in terms of the number of bytes requested rather than the number of calls, and we wanted the top caller to appear at the top, we can use - the 'sort' parameter, along with the 'descending' modifier: + the 'sort' parameter, along with the 'descending' modifier:: # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -922,7 +925,7 @@ The following commands are supported: Dropped: 0 To display the offset and size information in addition to the symbol - name, just use 'sym-offset' instead: + name, just use 'sym-offset' instead:: # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -961,7 +964,7 @@ The following commands are supported: We can also add multiple fields to the 'values' parameter. For example, we might want to see the total number of bytes allocated alongside bytes requested, and display the result sorted by bytes - allocated in a descending order: + allocated in a descending order:: # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -1004,7 +1007,7 @@ The following commands are supported: the hist trigger display symbolic call_sites, we can have the hist trigger additionally display the complete set of kernel stack traces that led to each call_site. To do that, we simply use the special - value 'stacktrace' for the key parameter: + value 'stacktrace' for the key parameter:: # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger @@ -1015,7 +1018,7 @@ The following commands are supported: event, along with a running total of any of the event fields for that event. Here we tally bytes requested and bytes allocated for every callpath in the system that led up to a kmalloc (in this case - every callpath to a kmalloc for a kernel compile): + every callpath to a kmalloc for a kernel compile):: # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active] @@ -1113,7 +1116,7 @@ The following commands are supported: gather and display sorted totals for each process, you can use the special .execname modifier to display the executable names for the processes in the table rather than raw pids. The example below - keeps a per-process sum of total bytes read: + keeps a per-process sum of total bytes read:: # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \ /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger @@ -1154,7 +1157,7 @@ The following commands are supported: gather and display a list of systemwide syscall hits, you can use the special .syscall modifier to display the syscall names rather than raw ids. The example below keeps a running total of syscall - counts for the system during the run: + counts for the system during the run:: # echo 'hist:key=id.syscall:val=hitcount' > \ /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger @@ -1196,155 +1199,155 @@ The following commands are supported: Entries: 72 Dropped: 0 - The syscall counts above provide a rough overall picture of system - call activity on the system; we can see for example that the most - popular system call on this system was the 'sys_ioctl' system call. - - We can use 'compound' keys to refine that number and provide some - further insight as to which processes exactly contribute to the - overall ioctl count. - - The command below keeps a hitcount for every unique combination of - system call id and pid - the end result is essentially a table - that keeps a per-pid sum of system call hits. The results are - sorted using the system call id as the primary key, and the - hitcount sum as the secondary key: - - # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \ - /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger - - # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist - # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active] - - { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1 - { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1 - { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1 - { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1 - { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2 - { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2 - { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2 - { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2 - { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2 - { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2 - . - . - . - { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12 - { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16 - { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808 - { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580 - . - . - . - { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3 - { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16 - { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2 - { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4 - { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4 - { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4 - { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4 - { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6 - { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2 - { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4 - { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6 - - Totals: - Hits: 31536 - Entries: 323 - Dropped: 0 - - The above list does give us a breakdown of the ioctl syscall by - pid, but it also gives us quite a bit more than that, which we - don't really care about at the moment. Since we know the syscall - id for sys_ioctl (16, displayed next to the sys_ioctl name), we - can use that to filter out all the other syscalls: - - # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \ - /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger - - # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist - # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active] - - { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1 - { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1 - . - . - . - { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45 - { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48 - { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48 - { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66 - { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674 - { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443 - - Totals: - Hits: 101162 - Entries: 103 - Dropped: 0 - - The above output shows that 'compiz' and 'Xorg' are far and away - the heaviest ioctl callers (which might lead to questions about - whether they really need to be making all those calls and to - possible avenues for further investigation.) - - The compound key examples used a key and a sum value (hitcount) to - sort the output, but we can just as easily use two keys instead. - Here's an example where we use a compound key composed of the the - common_pid and size event fields. Sorting with pid as the primary - key and 'size' as the secondary key allows us to display an - ordered summary of the recvfrom sizes, with counts, received by - each process: - - # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \ - /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger - - # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist - # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active] - - { common_pid: smbd [ 784], size: 4 } hitcount: 1 - { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672 - { common_pid: postgres [ 1796], size: 1000 } hitcount: 6 - { common_pid: postgres [ 1867], size: 1000 } hitcount: 10 - { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2 - { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1 - { common_pid: compiz [ 2994], size: 8 } hitcount: 1 - { common_pid: compiz [ 2994], size: 20 } hitcount: 11 - { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2 - { common_pid: firefox [ 8817], size: 4 } hitcount: 1 - { common_pid: firefox [ 8817], size: 8 } hitcount: 5 - { common_pid: firefox [ 8817], size: 588 } hitcount: 2 - { common_pid: firefox [ 8817], size: 628 } hitcount: 1 - { common_pid: firefox [ 8817], size: 6944 } hitcount: 1 - { common_pid: firefox [ 8817], size: 408880 } hitcount: 2 - { common_pid: firefox [ 8822], size: 8 } hitcount: 2 - { common_pid: firefox [ 8822], size: 160 } hitcount: 2 - { common_pid: firefox [ 8822], size: 320 } hitcount: 2 - { common_pid: firefox [ 8822], size: 352 } hitcount: 1 - . - . - . - { common_pid: pool [ 8923], size: 1960 } hitcount: 10 - { common_pid: pool [ 8923], size: 2048 } hitcount: 10 - { common_pid: pool [ 8924], size: 1960 } hitcount: 10 - { common_pid: pool [ 8924], size: 2048 } hitcount: 10 - { common_pid: pool [ 8928], size: 1964 } hitcount: 4 - { common_pid: pool [ 8928], size: 1965 } hitcount: 2 - { common_pid: pool [ 8928], size: 2048 } hitcount: 6 - { common_pid: pool [ 8929], size: 1982 } hitcount: 1 - { common_pid: pool [ 8929], size: 2048 } hitcount: 1 - - Totals: - Hits: 2016 - Entries: 224 - Dropped: 0 + The syscall counts above provide a rough overall picture of system + call activity on the system; we can see for example that the most + popular system call on this system was the 'sys_ioctl' system call. + + We can use 'compound' keys to refine that number and provide some + further insight as to which processes exactly contribute to the + overall ioctl count. + + The command below keeps a hitcount for every unique combination of + system call id and pid - the end result is essentially a table + that keeps a per-pid sum of system call hits. The results are + sorted using the system call id as the primary key, and the + hitcount sum as the secondary key:: + + # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \ + /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger + + # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist + # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active] + + { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1 + { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1 + { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1 + { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1 + { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2 + { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2 + { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2 + { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2 + { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2 + { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2 + . + . + . + { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12 + { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16 + { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808 + { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580 + . + . + . + { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3 + { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6 + { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2 + { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4 + { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6 + + Totals: + Hits: 31536 + Entries: 323 + Dropped: 0 + + The above list does give us a breakdown of the ioctl syscall by + pid, but it also gives us quite a bit more than that, which we + don't really care about at the moment. Since we know the syscall + id for sys_ioctl (16, displayed next to the sys_ioctl name), we + can use that to filter out all the other syscalls:: + + # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \ + /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger + + # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist + # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active] + + { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1 + . + . + . + { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45 + { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48 + { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48 + { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66 + { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674 + { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443 + + Totals: + Hits: 101162 + Entries: 103 + Dropped: 0 + + The above output shows that 'compiz' and 'Xorg' are far and away + the heaviest ioctl callers (which might lead to questions about + whether they really need to be making all those calls and to + possible avenues for further investigation.) + + The compound key examples used a key and a sum value (hitcount) to + sort the output, but we can just as easily use two keys instead. + Here's an example where we use a compound key composed of the the + common_pid and size event fields. Sorting with pid as the primary + key and 'size' as the secondary key allows us to display an + ordered summary of the recvfrom sizes, with counts, received by + each process:: + + # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger + + # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist + # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active] + + { common_pid: smbd [ 784], size: 4 } hitcount: 1 + { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672 + { common_pid: postgres [ 1796], size: 1000 } hitcount: 6 + { common_pid: postgres [ 1867], size: 1000 } hitcount: 10 + { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2 + { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1 + { common_pid: compiz [ 2994], size: 8 } hitcount: 1 + { common_pid: compiz [ 2994], size: 20 } hitcount: 11 + { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2 + { common_pid: firefox [ 8817], size: 4 } hitcount: 1 + { common_pid: firefox [ 8817], size: 8 } hitcount: 5 + { common_pid: firefox [ 8817], size: 588 } hitcount: 2 + { common_pid: firefox [ 8817], size: 628 } hitcount: 1 + { common_pid: firefox [ 8817], size: 6944 } hitcount: 1 + { common_pid: firefox [ 8817], size: 408880 } hitcount: 2 + { common_pid: firefox [ 8822], size: 8 } hitcount: 2 + { common_pid: firefox [ 8822], size: 160 } hitcount: 2 + { common_pid: firefox [ 8822], size: 320 } hitcount: 2 + { common_pid: firefox [ 8822], size: 352 } hitcount: 1 + . + . + . + { common_pid: pool [ 8923], size: 1960 } hitcount: 10 + { common_pid: pool [ 8923], size: 2048 } hitcount: 10 + { common_pid: pool [ 8924], size: 1960 } hitcount: 10 + { common_pid: pool [ 8924], size: 2048 } hitcount: 10 + { common_pid: pool [ 8928], size: 1964 } hitcount: 4 + { common_pid: pool [ 8928], size: 1965 } hitcount: 2 + { common_pid: pool [ 8928], size: 2048 } hitcount: 6 + { common_pid: pool [ 8929], size: 1982 } hitcount: 1 + { common_pid: pool [ 8929], size: 2048 } hitcount: 1 + + Totals: + Hits: 2016 + Entries: 224 + Dropped: 0 The above example also illustrates the fact that although a compound key is treated as a single entity for hashing purposes, the sub-keys @@ -1354,7 +1357,7 @@ The following commands are supported: demonstrates how you can manually pause and continue a hist trigger. In this example, we'll aggregate fork counts and don't expect a large number of entries in the hash table, so we'll drop it to a - much smaller number, say 256: + much smaller number, say 256:: # echo 'hist:key=child_comm:val=hitcount:size=256' > \ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger @@ -1390,7 +1393,7 @@ The following commands are supported: If we want to pause the hist trigger, we can simply append :pause to the command that started the trigger. Notice that the trigger info - displays as [paused]: + displays as [paused]:: # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger @@ -1427,7 +1430,7 @@ The following commands are supported: To manually continue having the trigger aggregate events, append :cont instead. Notice that the trigger info displays as [active] - again, and the data has changed: + again, and the data has changed:: # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger @@ -1481,7 +1484,7 @@ The following commands are supported: wget. First we set up an initially paused stacktrace trigger on the - netif_receive_skb event: + netif_receive_skb event:: # echo 'hist:key=stacktrace:vals=len:pause' > \ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger @@ -1492,7 +1495,7 @@ The following commands are supported: set up on netif_receive_skb if and only if it sees a sched_process_exec event with a filename of '/usr/bin/wget'. When that happens, all netif_receive_skb events are aggregated into a - hash table keyed on stacktrace: + hash table keyed on stacktrace:: # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger @@ -1500,7 +1503,7 @@ The following commands are supported: The aggregation continues until the netif_receive_skb is paused again, which is what the following disable_hist event does by creating a similar setup on the sched_process_exit event, using the - filter 'comm==wget': + filter 'comm==wget':: # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \ /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger @@ -1512,7 +1515,7 @@ The following commands are supported: The overall effect is that netif_receive_skb events are aggregated into the hash table for only the duration of the wget. Executing a wget command and then listing the 'hist' file will display the - output generated by the wget command: + output generated by the wget command:: $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz @@ -1597,13 +1600,13 @@ The following commands are supported: Suppose we wanted to try another run of the previous example but this time also wanted to see the complete list of events that went into the histogram. In order to avoid having to set everything up - again, we can just clear the histogram first: + again, we can just clear the histogram first:: # echo 'hist:key=stacktrace:vals=len:clear' >> \ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger Just to verify that it is in fact cleared, here's what we now see in - the hist file: + the hist file:: # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused] @@ -1617,7 +1620,7 @@ The following commands are supported: event occurring during the new run, which are in fact the same events being aggregated into the hash table, we add some additional 'enable_event' events to the triggering sched_process_exec and - sched_process_exit events as such: + sched_process_exit events as such:: # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \ /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger @@ -1628,7 +1631,7 @@ The following commands are supported: If you read the trigger files for the sched_process_exec and sched_process_exit triggers, you should see two triggers for each: one enabling/disabling the hist aggregation and the other - enabling/disabling the logging of events: + enabling/disabling the logging of events:: # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget @@ -1642,13 +1645,13 @@ The following commands are supported: sched_process_exit events is hit and matches 'wget', it enables or disables both the histogram and the event log, and what you end up with is a hash table and set of events just covering the specified - duration. Run the wget command again: + duration. Run the wget command again:: $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz Displaying the 'hist' file should show something similar to what you saw in the last run, but this time you should also see the - individual events in the trace file: + individual events in the trace file:: # cat /sys/kernel/debug/tracing/trace @@ -1673,15 +1676,15 @@ The following commands are supported: irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948 irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948 irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500 - . - . - . + .... + The following example demonstrates how multiple hist triggers can be attached to a given event. This capability can be useful for creating a set of different summaries derived from the same set of events, or for comparing the effects of different filters, among other things. + :: # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger @@ -1702,7 +1705,7 @@ The following commands are supported: any existing hist triggers beforehand). Displaying the contents of the 'hist' file for the event shows the - contents of all five histograms: + contents of all five histograms:: # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist @@ -1822,7 +1825,7 @@ The following commands are supported: output of events generated by tracepoints contained inside inline functions, but names can be used in a hist trigger on any event. For example, these two triggers when hit will update the same 'len' - field in the shared 'foo' histogram data: + field in the shared 'foo' histogram data:: # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \ /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger @@ -1830,7 +1833,7 @@ The following commands are supported: /sys/kernel/debug/tracing/events/net/netif_rx/trigger You can see that they're updating common histogram data by reading - each event's hist files at the same time: + each event's hist files at the same time:: # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist; cat /sys/kernel/debug/tracing/events/net/netif_rx/hist @@ -1943,7 +1946,7 @@ The following commands are supported: And here's an example that shows how to combine histogram data from any two events even if they don't share any 'compatible' fields other than 'hitcount' and 'stacktrace'. These commands create a - couple of triggers named 'bar' using those fields: + couple of triggers named 'bar' using those fields:: # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \ /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger @@ -1951,7 +1954,7 @@ The following commands are supported: /sys/kernel/debug/tracing/events/net/netif_rx/trigger And displaying the output of either shows some interesting if - somewhat confusing output: + somewhat confusing output:: # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.rst index a273dd0bbaaa..a8e22e0db63c 100644 --- a/Documentation/trace/ftrace-design.txt +++ b/Documentation/trace/ftrace-design.rst @@ -1,6 +1,12 @@ - function tracer guts - ==================== - By Mike Frysinger +====================== +Function Tracer Design +====================== + +:Author: Mike Frysinger + +.. caution:: + This document is out of date. Some of the description below doesn't + match current implementation now. Introduction ------------ @@ -21,8 +27,8 @@ Prerequisites ------------- Ftrace relies on these features being implemented: - STACKTRACE_SUPPORT - implement save_stack_trace() - TRACE_IRQFLAGS_SUPPORT - implement include/asm/irqflags.h + - STACKTRACE_SUPPORT - implement save_stack_trace() + - TRACE_IRQFLAGS_SUPPORT - implement include/asm/irqflags.h HAVE_FUNCTION_TRACER @@ -32,9 +38,11 @@ You will need to implement the mcount and the ftrace_stub functions. The exact mcount symbol name will depend on your toolchain. Some call it "mcount", "_mcount", or even "__mcount". You can probably figure it out by -running something like: +running something like:: + $ echo 'main(){}' | gcc -x c -S -o - - -pg | grep mcount call mcount + We'll make the assumption below that the symbol is "mcount" just to keep things nice and simple in the examples. @@ -56,8 +64,9 @@ size of the mcount call that is embedded in the function). For example, if the function foo() calls bar(), when the bar() function calls mcount(), the arguments mcount() will pass to the tracer are: - "frompc" - the address bar() will use to return to foo() - "selfpc" - the address bar() (with mcount() size adjustment) + + - "frompc" - the address bar() will use to return to foo() + - "selfpc" - the address bar() (with mcount() size adjustment) Also keep in mind that this mcount function will be called *a lot*, so optimizing for the default case of no tracer will help the smooth running of @@ -67,39 +76,41 @@ means the code flow should usually be kept linear (i.e. no branching in the nop case). This is of course an optimization and not a hard requirement. Here is some pseudo code that should help (these functions should actually be -implemented in assembly): +implemented in assembly):: -void ftrace_stub(void) -{ - return; -} + void ftrace_stub(void) + { + return; + } -void mcount(void) -{ - /* save any bare state needed in order to do initial checking */ + void mcount(void) + { + /* save any bare state needed in order to do initial checking */ - extern void (*ftrace_trace_function)(unsigned long, unsigned long); - if (ftrace_trace_function != ftrace_stub) - goto do_trace; + extern void (*ftrace_trace_function)(unsigned long, unsigned long); + if (ftrace_trace_function != ftrace_stub) + goto do_trace; - /* restore any bare state */ + /* restore any bare state */ - return; + return; -do_trace: + do_trace: - /* save all state needed by the ABI (see paragraph above) */ + /* save all state needed by the ABI (see paragraph above) */ - unsigned long frompc = ...; - unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; - ftrace_trace_function(frompc, selfpc); + unsigned long frompc = ...; + unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; + ftrace_trace_function(frompc, selfpc); - /* restore all state needed by the ABI */ -} + /* restore all state needed by the ABI */ + } Don't forget to export mcount for modules ! -extern void mcount(void); -EXPORT_SYMBOL(mcount); +:: + + extern void mcount(void); + EXPORT_SYMBOL(mcount); HAVE_FUNCTION_GRAPH_TRACER @@ -127,38 +138,40 @@ That function will simply call the common ftrace_return_to_handler function and that will return the original return address with which you can return to the original call site. -Here is the updated mcount pseudo code: -void mcount(void) -{ -... - if (ftrace_trace_function != ftrace_stub) - goto do_trace; - -+#ifdef CONFIG_FUNCTION_GRAPH_TRACER -+ extern void (*ftrace_graph_return)(...); -+ extern void (*ftrace_graph_entry)(...); -+ if (ftrace_graph_return != ftrace_stub || -+ ftrace_graph_entry != ftrace_graph_entry_stub) -+ ftrace_graph_caller(); -+#endif - - /* restore any bare state */ -... - -Here is the pseudo code for the new ftrace_graph_caller assembly function: -#ifdef CONFIG_FUNCTION_GRAPH_TRACER -void ftrace_graph_caller(void) -{ - /* save all state needed by the ABI */ - - unsigned long *frompc = &...; - unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; - /* passing frame pointer up is optional -- see below */ - prepare_ftrace_return(frompc, selfpc, frame_pointer); - - /* restore all state needed by the ABI */ -} -#endif +Here is the updated mcount pseudo code:: + + void mcount(void) + { + ... + if (ftrace_trace_function != ftrace_stub) + goto do_trace; + + +#ifdef CONFIG_FUNCTION_GRAPH_TRACER + + extern void (*ftrace_graph_return)(...); + + extern void (*ftrace_graph_entry)(...); + + if (ftrace_graph_return != ftrace_stub || + + ftrace_graph_entry != ftrace_graph_entry_stub) + + ftrace_graph_caller(); + +#endif + + /* restore any bare state */ + ... + +Here is the pseudo code for the new ftrace_graph_caller assembly function:: + + #ifdef CONFIG_FUNCTION_GRAPH_TRACER + void ftrace_graph_caller(void) + { + /* save all state needed by the ABI */ + + unsigned long *frompc = &...; + unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; + /* passing frame pointer up is optional -- see below */ + prepare_ftrace_return(frompc, selfpc, frame_pointer); + + /* restore all state needed by the ABI */ + } + #endif For information on how to implement prepare_ftrace_return(), simply look at the x86 version (the frame pointer passing is optional; see the next section for @@ -171,20 +184,21 @@ that the ABI that applies here is different from what applies to the mcount code. Since you are returning from a function (after the epilogue), you might be able to skimp on things saved/restored (usually just registers used to pass return values). +:: -#ifdef CONFIG_FUNCTION_GRAPH_TRACER -void return_to_handler(void) -{ - /* save all state needed by the ABI (see paragraph above) */ + #ifdef CONFIG_FUNCTION_GRAPH_TRACER + void return_to_handler(void) + { + /* save all state needed by the ABI (see paragraph above) */ - void (*original_return_point)(void) = ftrace_return_to_handler(); + void (*original_return_point)(void) = ftrace_return_to_handler(); - /* restore all state needed by the ABI */ + /* restore all state needed by the ABI */ - /* this is usually either a return or a jump */ - original_return_point(); -} -#endif + /* this is usually either a return or a jump */ + original_return_point(); + } + #endif HAVE_FUNCTION_GRAPH_FP_TEST @@ -228,20 +242,20 @@ HAVE_SYSCALL_TRACEPOINTS You need very few things to get the syscalls tracing in an arch. -- Support HAVE_ARCH_TRACEHOOK (see arch/Kconfig). -- Have a NR_syscalls variable in <asm/unistd.h> that provides the number - of syscalls supported by the arch. -- Support the TIF_SYSCALL_TRACEPOINT thread flags. -- Put the trace_sys_enter() and trace_sys_exit() tracepoints calls from ptrace - in the ptrace syscalls tracing path. -- If the system call table on this arch is more complicated than a simple array - of addresses of the system calls, implement an arch_syscall_addr to return - the address of a given system call. -- If the symbol names of the system calls do not match the function names on - this arch, define ARCH_HAS_SYSCALL_MATCH_SYM_NAME in asm/ftrace.h and - implement arch_syscall_match_sym_name with the appropriate logic to return - true if the function name corresponds with the symbol name. -- Tag this arch as HAVE_SYSCALL_TRACEPOINTS. + - Support HAVE_ARCH_TRACEHOOK (see arch/Kconfig). + - Have a NR_syscalls variable in <asm/unistd.h> that provides the number + of syscalls supported by the arch. + - Support the TIF_SYSCALL_TRACEPOINT thread flags. + - Put the trace_sys_enter() and trace_sys_exit() tracepoints calls from ptrace + in the ptrace syscalls tracing path. + - If the system call table on this arch is more complicated than a simple array + of addresses of the system calls, implement an arch_syscall_addr to return + the address of a given system call. + - If the symbol names of the system calls do not match the function names on + this arch, define ARCH_HAS_SYSCALL_MATCH_SYM_NAME in asm/ftrace.h and + implement arch_syscall_match_sym_name with the appropriate logic to return + true if the function name corresponds with the symbol name. + - Tag this arch as HAVE_SYSCALL_TRACEPOINTS. HAVE_FTRACE_MCOUNT_RECORD @@ -276,22 +290,28 @@ Once those are out of the way, you will need to implement: First you will need to fill out some arch details in your asm/ftrace.h. -Define MCOUNT_ADDR as the address of your mcount symbol similar to: +Define MCOUNT_ADDR as the address of your mcount symbol similar to:: + #define MCOUNT_ADDR ((unsigned long)mcount) -Since no one else will have a decl for that function, you will need to: + +Since no one else will have a decl for that function, you will need to:: + extern void mcount(void); You will also need the helper function ftrace_call_adjust(). Most people -will be able to stub it out like so: +will be able to stub it out like so:: + static inline unsigned long ftrace_call_adjust(unsigned long addr) { return addr; } + <details to be filled> Lastly you will need the custom dyn_arch_ftrace structure. If you need some extra state when runtime patching arbitrary call sites, this is the -place. For now though, create an empty struct: +place. For now though, create an empty struct:: + struct dyn_arch_ftrace { /* No extra data needed */ }; @@ -306,28 +326,28 @@ easier to have two separate definitions split up by #ifdefs. Same goes for the ftrace_stub() as that will now be inlined in ftrace_caller(). Before we get confused anymore, let's check out some pseudo code so you can -implement your own stuff in assembly: +implement your own stuff in assembly:: -void mcount(void) -{ - return; -} + void mcount(void) + { + return; + } -void ftrace_caller(void) -{ - /* save all state needed by the ABI (see paragraph above) */ + void ftrace_caller(void) + { + /* save all state needed by the ABI (see paragraph above) */ - unsigned long frompc = ...; - unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; + unsigned long frompc = ...; + unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; -ftrace_call: - ftrace_stub(frompc, selfpc); + ftrace_call: + ftrace_stub(frompc, selfpc); - /* restore all state needed by the ABI */ + /* restore all state needed by the ABI */ -ftrace_stub: - return; -} + ftrace_stub: + return; + } This might look a little odd at first, but keep in mind that we will be runtime patching multiple things. First, only functions that we actually want to trace @@ -341,21 +361,23 @@ order to make it through the next section. Every arch has an init callback function. If you need to do something early on to initialize some state, this is the time to do that. Otherwise, this simple -function below should be sufficient for most people: +function below should be sufficient for most people:: -int __init ftrace_dyn_arch_init(void) -{ - return 0; -} + int __init ftrace_dyn_arch_init(void) + { + return 0; + } There are two functions that are used to do runtime patching of arbitrary functions. The first is used to turn the mcount call site into a nop (which is what helps us retain runtime performance when not tracing). The second is used to turn the mcount call site into a call to an arbitrary location (but typically that is ftracer_caller()). See the general function definition in -linux/ftrace.h for the functions: +linux/ftrace.h for the functions:: + ftrace_make_nop() ftrace_make_call() + The rec->ip value is the address of the mcount call site that was collected by the scripts/recordmcount.pl during build time. @@ -364,7 +386,8 @@ will be modifying the assembly code at the location of the ftrace_call symbol inside of the ftrace_caller() function. So you should have sufficient padding at that location to support the new function calls you'll be inserting. Some people will be using a "call" type instruction while others will be using a -"branch" type instruction. Specifically, the function is: +"branch" type instruction. Specifically, the function is:: + ftrace_update_ftrace_func() @@ -373,6 +396,7 @@ HAVE_DYNAMIC_FTRACE + HAVE_FUNCTION_GRAPH_TRACER The function grapher needs a few tweaks in order to work with dynamic ftrace. Basically, you will need to: + - update: - ftrace_caller() - ftrace_graph_call() @@ -382,7 +406,9 @@ Basically, you will need to: - ftrace_disable_ftrace_graph_caller() <details to be filled> + Quick notes: + - add a nop stub after the ftrace_call location named ftrace_graph_call; stub needs to be large enough to support a call to ftrace_graph_caller() - update ftrace_graph_caller() to work with being called by the new diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst index 3aed560a12ee..998a60a93015 100644 --- a/Documentation/trace/ftrace-uses.rst +++ b/Documentation/trace/ftrace-uses.rst @@ -21,13 +21,14 @@ how to use ftrace to implement your own function callbacks. The ftrace context ================== +.. warning:: -WARNING: The ability to add a callback to almost any function within the -kernel comes with risks. A callback can be called from any context -(normal, softirq, irq, and NMI). Callbacks can also be called just before -going to idle, during CPU bring up and takedown, or going to user space. -This requires extra care to what can be done inside a callback. A callback -can be called outside the protective scope of RCU. + The ability to add a callback to almost any function within the + kernel comes with risks. A callback can be called from any context + (normal, softirq, irq, and NMI). Callbacks can also be called just before + going to idle, during CPU bring up and takedown, or going to user space. + This requires extra care to what can be done inside a callback. A callback + can be called outside the protective scope of RCU. The ftrace infrastructure has some protections agains recursions and RCU but one must still be very careful how they use the callbacks. @@ -54,15 +55,15 @@ an ftrace_ops with ftrace: Both .flags and .private are optional. Only .func is required. -To enable tracing call:: +To enable tracing call: .. c:function:: register_ftrace_function(&ops); -To disable tracing call:: +To disable tracing call: .. c:function:: unregister_ftrace_function(&ops); -The above is defined by including the header:: +The above is defined by including the header: .. c:function:: #include <linux/ftrace.h> @@ -200,7 +201,7 @@ match a specific pattern. See Filter Commands in :file:`Documentation/trace/ftrace.txt`. -To just trace the schedule function:: +To just trace the schedule function: .. code-block:: c @@ -210,7 +211,7 @@ To add more functions, call the ftrace_set_filter() more than once with the @reset parameter set to zero. To remove the current filter set and replace it with new functions defined by @buf, have @reset be non-zero. -To remove all the filtered functions and trace all functions:: +To remove all the filtered functions and trace all functions: .. code-block:: c diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst new file mode 100644 index 000000000000..0bc33ad4a3f9 --- /dev/null +++ b/Documentation/trace/ftrace.rst @@ -0,0 +1,3332 @@ +======================== +ftrace - Function Tracer +======================== + +Copyright 2008 Red Hat Inc. + +:Author: Steven Rostedt <srostedt@redhat.com> +:License: The GNU Free Documentation License, Version 1.2 + (dual licensed under the GPL v2) +:Original Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton, + John Kacur, and David Teigland. + +- Written for: 2.6.28-rc2 +- Updated for: 3.10 +- Updated for: 4.13 - Copyright 2017 VMware Inc. Steven Rostedt +- Converted to rst format - Changbin Du <changbin.du@intel.com> + +Introduction +------------ + +Ftrace is an internal tracer designed to help out developers and +designers of systems to find what is going on inside the kernel. +It can be used for debugging or analyzing latencies and +performance issues that take place outside of user-space. + +Although ftrace is typically considered the function tracer, it +is really a frame work of several assorted tracing utilities. +There's latency tracing to examine what occurs between interrupts +disabled and enabled, as well as for preemption and from a time +a task is woken to the task is actually scheduled in. + +One of the most common uses of ftrace is the event tracing. +Through out the kernel is hundreds of static event points that +can be enabled via the tracefs file system to see what is +going on in certain parts of the kernel. + +See events.txt for more information. + + +Implementation Details +---------------------- + +See :doc:`ftrace-design` for details for arch porters and such. + + +The File System +--------------- + +Ftrace uses the tracefs file system to hold the control files as +well as the files to display output. + +When tracefs is configured into the kernel (which selecting any ftrace +option will do) the directory /sys/kernel/tracing will be created. To mount +this directory, you can add to your /etc/fstab file:: + + tracefs /sys/kernel/tracing tracefs defaults 0 0 + +Or you can mount it at run time with:: + + mount -t tracefs nodev /sys/kernel/tracing + +For quicker access to that directory you may want to make a soft link to +it:: + + ln -s /sys/kernel/tracing /tracing + +.. attention:: + + Before 4.1, all ftrace tracing control files were within the debugfs + file system, which is typically located at /sys/kernel/debug/tracing. + For backward compatibility, when mounting the debugfs file system, + the tracefs file system will be automatically mounted at: + + /sys/kernel/debug/tracing + + All files located in the tracefs file system will be located in that + debugfs file system directory as well. + +.. attention:: + + Any selected ftrace option will also create the tracefs file system. + The rest of the document will assume that you are in the ftrace directory + (cd /sys/kernel/tracing) and will only concentrate on the files within that + directory and not distract from the content with the extended + "/sys/kernel/tracing" path name. + +That's it! (assuming that you have ftrace configured into your kernel) + +After mounting tracefs you will have access to the control and output files +of ftrace. Here is a list of some of the key files: + + + Note: all time values are in microseconds. + + current_tracer: + + This is used to set or display the current tracer + that is configured. + + available_tracers: + + This holds the different types of tracers that + have been compiled into the kernel. The + tracers listed here can be configured by + echoing their name into current_tracer. + + tracing_on: + + This sets or displays whether writing to the trace + ring buffer is enabled. Echo 0 into this file to disable + the tracer or 1 to enable it. Note, this only disables + writing to the ring buffer, the tracing overhead may + still be occurring. + + The kernel function tracing_off() can be used within the + kernel to disable writing to the ring buffer, which will + set this file to "0". User space can re-enable tracing by + echoing "1" into the file. + + Note, the function and event trigger "traceoff" will also + set this file to zero and stop tracing. Which can also + be re-enabled by user space using this file. + + trace: + + This file holds the output of the trace in a human + readable format (described below). Note, tracing is temporarily + disabled while this file is being read (opened). + + trace_pipe: + + The output is the same as the "trace" file but this + file is meant to be streamed with live tracing. + Reads from this file will block until new data is + retrieved. Unlike the "trace" file, this file is a + consumer. This means reading from this file causes + sequential reads to display more current data. Once + data is read from this file, it is consumed, and + will not be read again with a sequential read. The + "trace" file is static, and if the tracer is not + adding more data, it will display the same + information every time it is read. This file will not + disable tracing while being read. + + trace_options: + + This file lets the user control the amount of data + that is displayed in one of the above output + files. Options also exist to modify how a tracer + or events work (stack traces, timestamps, etc). + + options: + + This is a directory that has a file for every available + trace option (also in trace_options). Options may also be set + or cleared by writing a "1" or "0" respectively into the + corresponding file with the option name. + + tracing_max_latency: + + Some of the tracers record the max latency. + For example, the maximum time that interrupts are disabled. + The maximum time is saved in this file. The max trace will also be + stored, and displayed by "trace". A new max trace will only be + recorded if the latency is greater than the value in this file + (in microseconds). + + By echoing in a time into this file, no latency will be recorded + unless it is greater than the time in this file. + + tracing_thresh: + + Some latency tracers will record a trace whenever the + latency is greater than the number in this file. + Only active when the file contains a number greater than 0. + (in microseconds) + + buffer_size_kb: + + This sets or displays the number of kilobytes each CPU + buffer holds. By default, the trace buffers are the same size + for each CPU. The displayed number is the size of the + CPU buffer and not total size of all buffers. The + trace buffers are allocated in pages (blocks of memory + that the kernel uses for allocation, usually 4 KB in size). + If the last page allocated has room for more bytes + than requested, the rest of the page will be used, + making the actual allocation bigger than requested or shown. + ( Note, the size may not be a multiple of the page size + due to buffer management meta-data. ) + + Buffer sizes for individual CPUs may vary + (see "per_cpu/cpu0/buffer_size_kb" below), and if they do + this file will show "X". + + buffer_total_size_kb: + + This displays the total combined size of all the trace buffers. + + free_buffer: + + If a process is performing tracing, and the ring buffer should be + shrunk "freed" when the process is finished, even if it were to be + killed by a signal, this file can be used for that purpose. On close + of this file, the ring buffer will be resized to its minimum size. + Having a process that is tracing also open this file, when the process + exits its file descriptor for this file will be closed, and in doing so, + the ring buffer will be "freed". + + It may also stop tracing if disable_on_free option is set. + + tracing_cpumask: + + This is a mask that lets the user only trace on specified CPUs. + The format is a hex string representing the CPUs. + + set_ftrace_filter: + + When dynamic ftrace is configured in (see the + section below "dynamic ftrace"), the code is dynamically + modified (code text rewrite) to disable calling of the + function profiler (mcount). This lets tracing be configured + in with practically no overhead in performance. This also + has a side effect of enabling or disabling specific functions + to be traced. Echoing names of functions into this file + will limit the trace to only those functions. + + The functions listed in "available_filter_functions" are what + can be written into this file. + + This interface also allows for commands to be used. See the + "Filter commands" section for more details. + + set_ftrace_notrace: + + This has an effect opposite to that of + set_ftrace_filter. Any function that is added here will not + be traced. If a function exists in both set_ftrace_filter + and set_ftrace_notrace, the function will _not_ be traced. + + set_ftrace_pid: + + Have the function tracer only trace the threads whose PID are + listed in this file. + + If the "function-fork" option is set, then when a task whose + PID is listed in this file forks, the child's PID will + automatically be added to this file, and the child will be + traced by the function tracer as well. This option will also + cause PIDs of tasks that exit to be removed from the file. + + set_event_pid: + + Have the events only trace a task with a PID listed in this file. + Note, sched_switch and sched_wake_up will also trace events + listed in this file. + + To have the PIDs of children of tasks with their PID in this file + added on fork, enable the "event-fork" option. That option will also + cause the PIDs of tasks to be removed from this file when the task + exits. + + set_graph_function: + + Functions listed in this file will cause the function graph + tracer to only trace these functions and the functions that + they call. (See the section "dynamic ftrace" for more details). + + set_graph_notrace: + + Similar to set_graph_function, but will disable function graph + tracing when the function is hit until it exits the function. + This makes it possible to ignore tracing functions that are called + by a specific function. + + available_filter_functions: + + This lists the functions that ftrace has processed and can trace. + These are the function names that you can pass to + "set_ftrace_filter" or "set_ftrace_notrace". + (See the section "dynamic ftrace" below for more details.) + + dyn_ftrace_total_info: + + This file is for debugging purposes. The number of functions that + have been converted to nops and are available to be traced. + + enabled_functions: + + This file is more for debugging ftrace, but can also be useful + in seeing if any function has a callback attached to it. + Not only does the trace infrastructure use ftrace function + trace utility, but other subsystems might too. This file + displays all functions that have a callback attached to them + as well as the number of callbacks that have been attached. + Note, a callback may also call multiple functions which will + not be listed in this count. + + If the callback registered to be traced by a function with + the "save regs" attribute (thus even more overhead), a 'R' + will be displayed on the same line as the function that + is returning registers. + + If the callback registered to be traced by a function with + the "ip modify" attribute (thus the regs->ip can be changed), + an 'I' will be displayed on the same line as the function that + can be overridden. + + If the architecture supports it, it will also show what callback + is being directly called by the function. If the count is greater + than 1 it most likely will be ftrace_ops_list_func(). + + If the callback of the function jumps to a trampoline that is + specific to a the callback and not the standard trampoline, + its address will be printed as well as the function that the + trampoline calls. + + function_profile_enabled: + + When set it will enable all functions with either the function + tracer, or if configured, the function graph tracer. It will + keep a histogram of the number of functions that were called + and if the function graph tracer was configured, it will also keep + track of the time spent in those functions. The histogram + content can be displayed in the files: + + trace_stats/function<cpu> ( function0, function1, etc). + + trace_stats: + + A directory that holds different tracing stats. + + kprobe_events: + + Enable dynamic trace points. See kprobetrace.txt. + + kprobe_profile: + + Dynamic trace points stats. See kprobetrace.txt. + + max_graph_depth: + + Used with the function graph tracer. This is the max depth + it will trace into a function. Setting this to a value of + one will show only the first kernel function that is called + from user space. + + printk_formats: + + This is for tools that read the raw format files. If an event in + the ring buffer references a string, only a pointer to the string + is recorded into the buffer and not the string itself. This prevents + tools from knowing what that string was. This file displays the string + and address for the string allowing tools to map the pointers to what + the strings were. + + saved_cmdlines: + + Only the pid of the task is recorded in a trace event unless + the event specifically saves the task comm as well. Ftrace + makes a cache of pid mappings to comms to try to display + comms for events. If a pid for a comm is not listed, then + "<...>" is displayed in the output. + + If the option "record-cmd" is set to "0", then comms of tasks + will not be saved during recording. By default, it is enabled. + + saved_cmdlines_size: + + By default, 128 comms are saved (see "saved_cmdlines" above). To + increase or decrease the amount of comms that are cached, echo + in a the number of comms to cache, into this file. + + saved_tgids: + + If the option "record-tgid" is set, on each scheduling context switch + the Task Group ID of a task is saved in a table mapping the PID of + the thread to its TGID. By default, the "record-tgid" option is + disabled. + + snapshot: + + This displays the "snapshot" buffer and also lets the user + take a snapshot of the current running trace. + See the "Snapshot" section below for more details. + + stack_max_size: + + When the stack tracer is activated, this will display the + maximum stack size it has encountered. + See the "Stack Trace" section below. + + stack_trace: + + This displays the stack back trace of the largest stack + that was encountered when the stack tracer is activated. + See the "Stack Trace" section below. + + stack_trace_filter: + + This is similar to "set_ftrace_filter" but it limits what + functions the stack tracer will check. + + trace_clock: + + Whenever an event is recorded into the ring buffer, a + "timestamp" is added. This stamp comes from a specified + clock. By default, ftrace uses the "local" clock. This + clock is very fast and strictly per cpu, but on some + systems it may not be monotonic with respect to other + CPUs. In other words, the local clocks may not be in sync + with local clocks on other CPUs. + + Usual clocks for tracing:: + + # cat trace_clock + [local] global counter x86-tsc + + The clock with the square brackets around it is the one in effect. + + local: + Default clock, but may not be in sync across CPUs + + global: + This clock is in sync with all CPUs but may + be a bit slower than the local clock. + + counter: + This is not a clock at all, but literally an atomic + counter. It counts up one by one, but is in sync + with all CPUs. This is useful when you need to + know exactly the order events occurred with respect to + each other on different CPUs. + + uptime: + This uses the jiffies counter and the time stamp + is relative to the time since boot up. + + perf: + This makes ftrace use the same clock that perf uses. + Eventually perf will be able to read ftrace buffers + and this will help out in interleaving the data. + + x86-tsc: + Architectures may define their own clocks. For + example, x86 uses its own TSC cycle clock here. + + ppc-tb: + This uses the powerpc timebase register value. + This is in sync across CPUs and can also be used + to correlate events across hypervisor/guest if + tb_offset is known. + + mono: + This uses the fast monotonic clock (CLOCK_MONOTONIC) + which is monotonic and is subject to NTP rate adjustments. + + mono_raw: + This is the raw monotonic clock (CLOCK_MONOTONIC_RAW) + which is montonic but is not subject to any rate adjustments + and ticks at the same rate as the hardware clocksource. + + boot: + This is the boot clock (CLOCK_BOOTTIME) and is based on the + fast monotonic clock, but also accounts for time spent in + suspend. Since the clock access is designed for use in + tracing in the suspend path, some side effects are possible + if clock is accessed after the suspend time is accounted before + the fast mono clock is updated. In this case, the clock update + appears to happen slightly sooner than it normally would have. + Also on 32-bit systems, it's possible that the 64-bit boot offset + sees a partial update. These effects are rare and post + processing should be able to handle them. See comments in the + ktime_get_boot_fast_ns() function for more information. + + To set a clock, simply echo the clock name into this file:: + + echo global > trace_clock + + trace_marker: + + This is a very useful file for synchronizing user space + with events happening in the kernel. Writing strings into + this file will be written into the ftrace buffer. + + It is useful in applications to open this file at the start + of the application and just reference the file descriptor + for the file:: + + void trace_write(const char *fmt, ...) + { + va_list ap; + char buf[256]; + int n; + + if (trace_fd < 0) + return; + + va_start(ap, fmt); + n = vsnprintf(buf, 256, fmt, ap); + va_end(ap); + + write(trace_fd, buf, n); + } + + start:: + + trace_fd = open("trace_marker", WR_ONLY); + + trace_marker_raw: + + This is similar to trace_marker above, but is meant for for binary data + to be written to it, where a tool can be used to parse the data + from trace_pipe_raw. + + uprobe_events: + + Add dynamic tracepoints in programs. + See uprobetracer.txt + + uprobe_profile: + + Uprobe statistics. See uprobetrace.txt + + instances: + + This is a way to make multiple trace buffers where different + events can be recorded in different buffers. + See "Instances" section below. + + events: + + This is the trace event directory. It holds event tracepoints + (also known as static tracepoints) that have been compiled + into the kernel. It shows what event tracepoints exist + and how they are grouped by system. There are "enable" + files at various levels that can enable the tracepoints + when a "1" is written to them. + + See events.txt for more information. + + set_event: + + By echoing in the event into this file, will enable that event. + + See events.txt for more information. + + available_events: + + A list of events that can be enabled in tracing. + + See events.txt for more information. + + hwlat_detector: + + Directory for the Hardware Latency Detector. + See "Hardware Latency Detector" section below. + + per_cpu: + + This is a directory that contains the trace per_cpu information. + + per_cpu/cpu0/buffer_size_kb: + + The ftrace buffer is defined per_cpu. That is, there's a separate + buffer for each CPU to allow writes to be done atomically, + and free from cache bouncing. These buffers may have different + size buffers. This file is similar to the buffer_size_kb + file, but it only displays or sets the buffer size for the + specific CPU. (here cpu0). + + per_cpu/cpu0/trace: + + This is similar to the "trace" file, but it will only display + the data specific for the CPU. If written to, it only clears + the specific CPU buffer. + + per_cpu/cpu0/trace_pipe + + This is similar to the "trace_pipe" file, and is a consuming + read, but it will only display (and consume) the data specific + for the CPU. + + per_cpu/cpu0/trace_pipe_raw + + For tools that can parse the ftrace ring buffer binary format, + the trace_pipe_raw file can be used to extract the data + from the ring buffer directly. With the use of the splice() + system call, the buffer data can be quickly transferred to + a file or to the network where a server is collecting the + data. + + Like trace_pipe, this is a consuming reader, where multiple + reads will always produce different data. + + per_cpu/cpu0/snapshot: + + This is similar to the main "snapshot" file, but will only + snapshot the current CPU (if supported). It only displays + the content of the snapshot for a given CPU, and if + written to, only clears this CPU buffer. + + per_cpu/cpu0/snapshot_raw: + + Similar to the trace_pipe_raw, but will read the binary format + from the snapshot buffer for the given CPU. + + per_cpu/cpu0/stats: + + This displays certain stats about the ring buffer: + + entries: + The number of events that are still in the buffer. + + overrun: + The number of lost events due to overwriting when + the buffer was full. + + commit overrun: + Should always be zero. + This gets set if so many events happened within a nested + event (ring buffer is re-entrant), that it fills the + buffer and starts dropping events. + + bytes: + Bytes actually read (not overwritten). + + oldest event ts: + The oldest timestamp in the buffer + + now ts: + The current timestamp + + dropped events: + Events lost due to overwrite option being off. + + read events: + The number of events read. + +The Tracers +----------- + +Here is the list of current tracers that may be configured. + + "function" + + Function call tracer to trace all kernel functions. + + "function_graph" + + Similar to the function tracer except that the + function tracer probes the functions on their entry + whereas the function graph tracer traces on both entry + and exit of the functions. It then provides the ability + to draw a graph of function calls similar to C code + source. + + "blk" + + The block tracer. The tracer used by the blktrace user + application. + + "hwlat" + + The Hardware Latency tracer is used to detect if the hardware + produces any latency. See "Hardware Latency Detector" section + below. + + "irqsoff" + + Traces the areas that disable interrupts and saves + the trace with the longest max latency. + See tracing_max_latency. When a new max is recorded, + it replaces the old trace. It is best to view this + trace with the latency-format option enabled, which + happens automatically when the tracer is selected. + + "preemptoff" + + Similar to irqsoff but traces and records the amount of + time for which preemption is disabled. + + "preemptirqsoff" + + Similar to irqsoff and preemptoff, but traces and + records the largest time for which irqs and/or preemption + is disabled. + + "wakeup" + + Traces and records the max latency that it takes for + the highest priority task to get scheduled after + it has been woken up. + Traces all tasks as an average developer would expect. + + "wakeup_rt" + + Traces and records the max latency that it takes for just + RT tasks (as the current "wakeup" does). This is useful + for those interested in wake up timings of RT tasks. + + "wakeup_dl" + + Traces and records the max latency that it takes for + a SCHED_DEADLINE task to be woken (as the "wakeup" and + "wakeup_rt" does). + + "mmiotrace" + + A special tracer that is used to trace binary module. + It will trace all the calls that a module makes to the + hardware. Everything it writes and reads from the I/O + as well. + + "branch" + + This tracer can be configured when tracing likely/unlikely + calls within the kernel. It will trace when a likely and + unlikely branch is hit and if it was correct in its prediction + of being correct. + + "nop" + + This is the "trace nothing" tracer. To remove all + tracers from tracing simply echo "nop" into + current_tracer. + + +Examples of using the tracer +---------------------------- + +Here are typical examples of using the tracers when controlling +them only with the tracefs interface (without using any +user-land utilities). + +Output format: +-------------- + +Here is an example of the output format of the file "trace":: + + # tracer: function + # + # entries-in-buffer/entries-written: 140080/250280 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath + bash-1977 [000] .... 17284.993653: __close_fd <-sys_close + bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd + sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify + bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock + bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd + bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock + bash-1977 [000] .... 17284.993657: filp_close <-__close_fd + bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close + sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath + .... + +A header is printed with the tracer name that is represented by +the trace. In this case the tracer is "function". Then it shows the +number of events in the buffer as well as the total number of entries +that were written. The difference is the number of entries that were +lost due to the buffer filling up (250280 - 140080 = 110200 events +lost). + +The header explains the content of the events. Task name "bash", the task +PID "1977", the CPU that it was running on "000", the latency format +(explained below), the timestamp in <secs>.<usecs> format, the +function name that was traced "sys_close" and the parent function that +called this function "system_call_fastpath". The timestamp is the time +at which the function was entered. + +Latency trace format +-------------------- + +When the latency-format option is enabled or when one of the latency +tracers is set, the trace file gives somewhat more information to see +why a latency happened. Here is a typical trace:: + + # tracer: irqsoff + # + # irqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: __lock_task_sighand + # => ended at: _raw_spin_unlock_irqrestore + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand + ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore + ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore + ps-6143 2d..1 306us : <stack trace> + => trace_hardirqs_on_caller + => trace_hardirqs_on + => _raw_spin_unlock_irqrestore + => do_task_stat + => proc_tgid_stat + => proc_single_show + => seq_read + => vfs_read + => sys_read + => system_call_fastpath + + +This shows that the current tracer is "irqsoff" tracing the time +for which interrupts were disabled. It gives the trace version (which +never changes) and the version of the kernel upon which this was executed on +(3.8). Then it displays the max latency in microseconds (259 us). The number +of trace entries displayed and the total number (both are four: #4/4). +VP, KP, SP, and HP are always zero and are reserved for later use. +#P is the number of online CPUs (#P:4). + +The task is the process that was running when the latency +occurred. (ps pid: 6143). + +The start and stop (the functions in which the interrupts were +disabled and enabled respectively) that caused the latencies: + + - __lock_task_sighand is where the interrupts were disabled. + - _raw_spin_unlock_irqrestore is where they were enabled again. + +The next lines after the header are the trace itself. The header +explains which is which. + + cmd: The name of the process in the trace. + + pid: The PID of that process. + + CPU#: The CPU which the process was running on. + + irqs-off: 'd' interrupts are disabled. '.' otherwise. + .. caution:: If the architecture does not support a way to + read the irq flags variable, an 'X' will always + be printed here. + + need-resched: + - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set, + - 'n' only TIF_NEED_RESCHED is set, + - 'p' only PREEMPT_NEED_RESCHED is set, + - '.' otherwise. + + hardirq/softirq: + - 'Z' - NMI occurred inside a hardirq + - 'z' - NMI is running + - 'H' - hard irq occurred inside a softirq. + - 'h' - hard irq is running + - 's' - soft irq is running + - '.' - normal context. + + preempt-depth: The level of preempt_disabled + +The above is mostly meaningful for kernel developers. + + time: + When the latency-format option is enabled, the trace file + output includes a timestamp relative to the start of the + trace. This differs from the output when latency-format + is disabled, which includes an absolute timestamp. + + delay: + This is just to help catch your eye a bit better. And + needs to be fixed to be only relative to the same CPU. + The marks are determined by the difference between this + current trace and the next trace. + + - '$' - greater than 1 second + - '@' - greater than 100 milisecond + - '*' - greater than 10 milisecond + - '#' - greater than 1000 microsecond + - '!' - greater than 100 microsecond + - '+' - greater than 10 microsecond + - ' ' - less than or equal to 10 microsecond. + + The rest is the same as the 'trace' file. + + Note, the latency tracers will usually end with a back trace + to easily find where the latency occurred. + +trace_options +------------- + +The trace_options file (or the options directory) is used to control +what gets printed in the trace output, or manipulate the tracers. +To see what is available, simply cat the file:: + + cat trace_options + print-parent + nosym-offset + nosym-addr + noverbose + noraw + nohex + nobin + noblock + trace_printk + annotate + nouserstacktrace + nosym-userobj + noprintk-msg-only + context-info + nolatency-format + record-cmd + norecord-tgid + overwrite + nodisable_on_free + irq-info + markers + noevent-fork + function-trace + nofunction-fork + nodisplay-graph + nostacktrace + nobranch + +To disable one of the options, echo in the option prepended with +"no":: + + echo noprint-parent > trace_options + +To enable an option, leave off the "no":: + + echo sym-offset > trace_options + +Here are the available options: + + print-parent + On function traces, display the calling (parent) + function as well as the function being traced. + :: + + print-parent: + bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul + + noprint-parent: + bash-4000 [01] 1477.606694: simple_strtoul + + + sym-offset + Display not only the function name, but also the + offset in the function. For example, instead of + seeing just "ktime_get", you will see + "ktime_get+0xb/0x20". + :: + + sym-offset: + bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0 + + sym-addr + This will also display the function address as well + as the function name. + :: + + sym-addr: + bash-4000 [01] 1477.606694: simple_strtoul <c0339346> + + verbose + This deals with the trace file when the + latency-format option is enabled. + :: + + bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \ + (+0.000ms): simple_strtoul (kstrtoul) + + raw + This will display raw numbers. This option is best for + use with user applications that can translate the raw + numbers better than having it done in the kernel. + + hex + Similar to raw, but the numbers will be in a hexadecimal format. + + bin + This will print out the formats in raw binary. + + block + When set, reading trace_pipe will not block when polled. + + trace_printk + Can disable trace_printk() from writing into the buffer. + + annotate + It is sometimes confusing when the CPU buffers are full + and one CPU buffer had a lot of events recently, thus + a shorter time frame, were another CPU may have only had + a few events, which lets it have older events. When + the trace is reported, it shows the oldest events first, + and it may look like only one CPU ran (the one with the + oldest events). When the annotate option is set, it will + display when a new CPU buffer started:: + + <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on + <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on + <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore + ##### CPU 2 buffer started #### + <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle + <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog + <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock + + userstacktrace + This option changes the trace. It records a + stacktrace of the current user space thread after + each trace event. + + sym-userobj + when user stacktrace are enabled, look up which + object the address belongs to, and print a + relative address. This is especially useful when + ASLR is on, otherwise you don't get a chance to + resolve the address to object/file/line after + the app is no longer running + + The lookup is performed when you read + trace,trace_pipe. Example:: + + a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0 + x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] + + + printk-msg-only + When set, trace_printk()s will only show the format + and not their parameters (if trace_bprintk() or + trace_bputs() was used to save the trace_printk()). + + context-info + Show only the event data. Hides the comm, PID, + timestamp, CPU, and other useful data. + + latency-format + This option changes the trace output. When it is enabled, + the trace displays additional information about the + latency, as described in "Latency trace format". + + record-cmd + When any event or tracer is enabled, a hook is enabled + in the sched_switch trace point to fill comm cache + with mapped pids and comms. But this may cause some + overhead, and if you only care about pids, and not the + name of the task, disabling this option can lower the + impact of tracing. See "saved_cmdlines". + + record-tgid + When any event or tracer is enabled, a hook is enabled + in the sched_switch trace point to fill the cache of + mapped Thread Group IDs (TGID) mapping to pids. See + "saved_tgids". + + overwrite + This controls what happens when the trace buffer is + full. If "1" (default), the oldest events are + discarded and overwritten. If "0", then the newest + events are discarded. + (see per_cpu/cpu0/stats for overrun and dropped) + + disable_on_free + When the free_buffer is closed, tracing will + stop (tracing_on set to 0). + + irq-info + Shows the interrupt, preempt count, need resched data. + When disabled, the trace looks like:: + + # tracer: function + # + # entries-in-buffer/entries-written: 144405/9452052 #P:4 + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up + <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89 + <idle>-0 [002] 23636.756055: enqueue_task <-activate_task + + + markers + When set, the trace_marker is writable (only by root). + When disabled, the trace_marker will error with EINVAL + on write. + + event-fork + When set, tasks with PIDs listed in set_event_pid will have + the PIDs of their children added to set_event_pid when those + tasks fork. Also, when tasks with PIDs in set_event_pid exit, + their PIDs will be removed from the file. + + function-trace + The latency tracers will enable function tracing + if this option is enabled (default it is). When + it is disabled, the latency tracers do not trace + functions. This keeps the overhead of the tracer down + when performing latency tests. + + function-fork + When set, tasks with PIDs listed in set_ftrace_pid will + have the PIDs of their children added to set_ftrace_pid + when those tasks fork. Also, when tasks with PIDs in + set_ftrace_pid exit, their PIDs will be removed from the + file. + + display-graph + When set, the latency tracers (irqsoff, wakeup, etc) will + use function graph tracing instead of function tracing. + + stacktrace + When set, a stack trace is recorded after any trace event + is recorded. + + branch + Enable branch tracing with the tracer. This enables branch + tracer along with the currently set tracer. Enabling this + with the "nop" tracer is the same as just enabling the + "branch" tracer. + +.. tip:: Some tracers have their own options. They only appear in this + file when the tracer is active. They always appear in the + options directory. + + +Here are the per tracer options: + +Options for function tracer: + + func_stack_trace + When set, a stack trace is recorded after every + function that is recorded. NOTE! Limit the functions + that are recorded before enabling this, with + "set_ftrace_filter" otherwise the system performance + will be critically degraded. Remember to disable + this option before clearing the function filter. + +Options for function_graph tracer: + + Since the function_graph tracer has a slightly different output + it has its own options to control what is displayed. + + funcgraph-overrun + When set, the "overrun" of the graph stack is + displayed after each function traced. The + overrun, is when the stack depth of the calls + is greater than what is reserved for each task. + Each task has a fixed array of functions to + trace in the call graph. If the depth of the + calls exceeds that, the function is not traced. + The overrun is the number of functions missed + due to exceeding this array. + + funcgraph-cpu + When set, the CPU number of the CPU where the trace + occurred is displayed. + + funcgraph-overhead + When set, if the function takes longer than + A certain amount, then a delay marker is + displayed. See "delay" above, under the + header description. + + funcgraph-proc + Unlike other tracers, the process' command line + is not displayed by default, but instead only + when a task is traced in and out during a context + switch. Enabling this options has the command + of each process displayed at every line. + + funcgraph-duration + At the end of each function (the return) + the duration of the amount of time in the + function is displayed in microseconds. + + funcgraph-abstime + When set, the timestamp is displayed at each line. + + funcgraph-irqs + When disabled, functions that happen inside an + interrupt will not be traced. + + funcgraph-tail + When set, the return event will include the function + that it represents. By default this is off, and + only a closing curly bracket "}" is displayed for + the return of a function. + + sleep-time + When running function graph tracer, to include + the time a task schedules out in its function. + When enabled, it will account time the task has been + scheduled out as part of the function call. + + graph-time + When running function profiler with function graph tracer, + to include the time to call nested functions. When this is + not set, the time reported for the function will only + include the time the function itself executed for, not the + time for functions that it called. + +Options for blk tracer: + + blk_classic + Shows a more minimalistic output. + + +irqsoff +------- + +When interrupts are disabled, the CPU can not react to any other +external event (besides NMIs and SMIs). This prevents the timer +interrupt from triggering or the mouse interrupt from letting +the kernel know of a new mouse event. The result is a latency +with the reaction time. + +The irqsoff tracer tracks the time for which interrupts are +disabled. When a new maximum latency is hit, the tracer saves +the trace leading up to that latency point so that every time a +new maximum is reached, the old saved trace is discarded and the +new trace is saved. + +To reset the maximum, echo 0 into tracing_max_latency. Here is +an example:: + + # echo 0 > options/function-trace + # echo irqsoff > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # ls -ltr + [...] + # echo 0 > tracing_on + # cat trace + # tracer: irqsoff + # + # irqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: run_timer_softirq + # => ended at: run_timer_softirq + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq + <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq + <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq + <idle>-0 0dNs3 25us : <stack trace> + => _raw_spin_unlock_irq + => run_timer_softirq + => __do_softirq + => call_softirq + => do_softirq + => irq_exit + => smp_apic_timer_interrupt + => apic_timer_interrupt + => rcu_idle_exit + => cpu_idle + => rest_init + => start_kernel + => x86_64_start_reservations + => x86_64_start_kernel + +Here we see that that we had a latency of 16 microseconds (which is +very good). The _raw_spin_lock_irq in run_timer_softirq disabled +interrupts. The difference between the 16 and the displayed +timestamp 25us occurred because the clock was incremented +between the time of recording the max latency and the time of +recording the function that had that latency. + +Note the above example had function-trace not set. If we set +function-trace, we get a much larger output:: + + with echo 1 > options/function-trace + + # tracer: irqsoff + # + # irqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: ata_scsi_queuecmd + # => ended at: ata_scsi_queuecmd + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd + bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave + bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd + bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev + bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev + bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd + bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd + bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd + bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat + [...] + bash-2042 3d..1 67us : delay_tsc <-__delay + bash-2042 3d..1 67us : add_preempt_count <-delay_tsc + bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc + bash-2042 3d..1 67us : add_preempt_count <-delay_tsc + bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc + bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue + bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd + bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd + bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd + bash-2042 3d..1 120us : <stack trace> + => _raw_spin_unlock_irqrestore + => ata_scsi_queuecmd + => scsi_dispatch_cmd + => scsi_request_fn + => __blk_run_queue_uncond + => __blk_run_queue + => blk_queue_bio + => generic_make_request + => submit_bio + => submit_bh + => __ext3_get_inode_loc + => ext3_iget + => ext3_lookup + => lookup_real + => __lookup_hash + => walk_component + => lookup_last + => path_lookupat + => filename_lookup + => user_path_at_empty + => user_path_at + => vfs_fstatat + => vfs_stat + => sys_newstat + => system_call_fastpath + + +Here we traced a 71 microsecond latency. But we also see all the +functions that were called during that time. Note that by +enabling function tracing, we incur an added overhead. This +overhead may extend the latency times. But nevertheless, this +trace has provided some very helpful debugging information. + + +preemptoff +---------- + +When preemption is disabled, we may be able to receive +interrupts but the task cannot be preempted and a higher +priority task must wait for preemption to be enabled again +before it can preempt a lower priority task. + +The preemptoff tracer traces the places that disable preemption. +Like the irqsoff tracer, it records the maximum latency for +which preemption was disabled. The control of preemptoff tracer +is much like the irqsoff tracer. +:: + + # echo 0 > options/function-trace + # echo preemptoff > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # ls -ltr + [...] + # echo 0 > tracing_on + # cat trace + # tracer: preemptoff + # + # preemptoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: do_IRQ + # => ended at: do_IRQ + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ + sshd-1991 1d..1 46us : irq_exit <-do_IRQ + sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ + sshd-1991 1d..1 52us : <stack trace> + => sub_preempt_count + => irq_exit + => do_IRQ + => ret_from_intr + + +This has some more changes. Preemption was disabled when an +interrupt came in (notice the 'h'), and was enabled on exit. +But we also see that interrupts have been disabled when entering +the preempt off section and leaving it (the 'd'). We do not know if +interrupts were enabled in the mean time or shortly after this +was over. +:: + + # tracer: preemptoff + # + # preemptoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: wake_up_new_task + # => ended at: task_rq_unlock + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task + bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq + bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair + bash-1994 1d..1 1us : source_load <-select_task_rq_fair + bash-1994 1d..1 1us : source_load <-select_task_rq_fair + [...] + bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt + bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter + bash-1994 1d..1 13us : add_preempt_count <-irq_enter + bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt + bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt + bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt + bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock + bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt + [...] + bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event + bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt + bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit + bash-1994 1d..2 36us : do_softirq <-irq_exit + bash-1994 1d..2 36us : __do_softirq <-call_softirq + bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq + bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq + bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq + bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock + bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq + [...] + bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks + bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq + bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable + bash-1994 1dN.2 82us : idle_cpu <-irq_exit + bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit + bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit + bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock + bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock + bash-1994 1.N.1 104us : <stack trace> + => sub_preempt_count + => _raw_spin_unlock_irqrestore + => task_rq_unlock + => wake_up_new_task + => do_fork + => sys_clone + => stub_clone + + +The above is an example of the preemptoff trace with +function-trace set. Here we see that interrupts were not disabled +the entire time. The irq_enter code lets us know that we entered +an interrupt 'h'. Before that, the functions being traced still +show that it is not in an interrupt, but we can see from the +functions themselves that this is not the case. + +preemptirqsoff +-------------- + +Knowing the locations that have interrupts disabled or +preemption disabled for the longest times is helpful. But +sometimes we would like to know when either preemption and/or +interrupts are disabled. + +Consider the following code:: + + local_irq_disable(); + call_function_with_irqs_off(); + preempt_disable(); + call_function_with_irqs_and_preemption_off(); + local_irq_enable(); + call_function_with_preemption_off(); + preempt_enable(); + +The irqsoff tracer will record the total length of +call_function_with_irqs_off() and +call_function_with_irqs_and_preemption_off(). + +The preemptoff tracer will record the total length of +call_function_with_irqs_and_preemption_off() and +call_function_with_preemption_off(). + +But neither will trace the time that interrupts and/or +preemption is disabled. This total time is the time that we can +not schedule. To record this time, use the preemptirqsoff +tracer. + +Again, using this trace is much like the irqsoff and preemptoff +tracers. +:: + + # echo 0 > options/function-trace + # echo preemptirqsoff > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # ls -ltr + [...] + # echo 0 > tracing_on + # cat trace + # tracer: preemptirqsoff + # + # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: ata_scsi_queuecmd + # => ended at: ata_scsi_queuecmd + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd + ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd + ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd + ls-2230 3...1 111us : <stack trace> + => sub_preempt_count + => _raw_spin_unlock_irqrestore + => ata_scsi_queuecmd + => scsi_dispatch_cmd + => scsi_request_fn + => __blk_run_queue_uncond + => __blk_run_queue + => blk_queue_bio + => generic_make_request + => submit_bio + => submit_bh + => ext3_bread + => ext3_dir_bread + => htree_dirblock_to_tree + => ext3_htree_fill_tree + => ext3_readdir + => vfs_readdir + => sys_getdents + => system_call_fastpath + + +The trace_hardirqs_off_thunk is called from assembly on x86 when +interrupts are disabled in the assembly code. Without the +function tracing, we do not know if interrupts were enabled +within the preemption points. We do see that it started with +preemption enabled. + +Here is a trace with function-trace set:: + + # tracer: preemptirqsoff + # + # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: schedule + # => ended at: mutex_unlock + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + kworker/-59 3...1 0us : __schedule <-schedule + kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch + kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq + kworker/-59 3d..2 1us : deactivate_task <-__schedule + kworker/-59 3d..2 1us : dequeue_task <-deactivate_task + kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task + kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task + kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair + kworker/-59 3d..2 2us : update_min_vruntime <-update_curr + kworker/-59 3d..2 3us : cpuacct_charge <-update_curr + kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge + kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge + kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair + kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair + kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair + kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair + kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair + kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair + kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule + kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping + kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule + kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task + kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair + kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair + kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity + ls-2269 3d..2 7us : finish_task_switch <-__schedule + ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch + ls-2269 3d..2 8us : do_IRQ <-ret_from_intr + ls-2269 3d..2 8us : irq_enter <-do_IRQ + ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter + ls-2269 3d..2 9us : add_preempt_count <-irq_enter + ls-2269 3d.h2 9us : exit_idle <-do_IRQ + [...] + ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock + ls-2269 3d.h2 20us : irq_exit <-do_IRQ + ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit + ls-2269 3d..3 21us : do_softirq <-irq_exit + ls-2269 3d..3 21us : __do_softirq <-call_softirq + ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq + ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip + ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip + ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr + ls-2269 3d.s5 31us : irq_enter <-do_IRQ + ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter + [...] + ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter + ls-2269 3d.s5 32us : add_preempt_count <-irq_enter + ls-2269 3d.H5 32us : exit_idle <-do_IRQ + ls-2269 3d.H5 32us : handle_irq <-do_IRQ + ls-2269 3d.H5 32us : irq_to_desc <-handle_irq + ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq + [...] + ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll + ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action + ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq + ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable + ls-2269 3d..3 159us : idle_cpu <-irq_exit + ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit + ls-2269 3d..3 160us : sub_preempt_count <-irq_exit + ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock + ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock + ls-2269 3d... 186us : <stack trace> + => __mutex_unlock_slowpath + => mutex_unlock + => process_output + => n_tty_write + => tty_write + => vfs_write + => sys_write + => system_call_fastpath + +This is an interesting trace. It started with kworker running and +scheduling out and ls taking over. But as soon as ls released the +rq lock and enabled interrupts (but not preemption) an interrupt +triggered. When the interrupt finished, it started running softirqs. +But while the softirq was running, another interrupt triggered. +When an interrupt is running inside a softirq, the annotation is 'H'. + + +wakeup +------ + +One common case that people are interested in tracing is the +time it takes for a task that is woken to actually wake up. +Now for non Real-Time tasks, this can be arbitrary. But tracing +it none the less can be interesting. + +Without function tracing:: + + # echo 0 > options/function-trace + # echo wakeup > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # chrt -f 5 sleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: wakeup + # + # wakeup latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H + <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 3d..3 15us : __schedule <-schedule + <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H + +The tracer only traces the highest priority task in the system +to avoid tracing the normal circumstances. Here we see that +the kworker with a nice priority of -20 (not very nice), took +just 15 microseconds from the time it woke up, to the time it +ran. + +Non Real-Time tasks are not that interesting. A more interesting +trace is to concentrate only on Real-Time tasks. + +wakeup_rt +--------- + +In a Real-Time environment it is very important to know the +wakeup time it takes for the highest priority task that is woken +up to the time that it executes. This is also known as "schedule +latency". I stress the point that this is about RT tasks. It is +also important to know the scheduling latency of non-RT tasks, +but the average schedule latency is better for non-RT tasks. +Tools like LatencyTop are more appropriate for such +measurements. + +Real-Time environments are interested in the worst case latency. +That is the longest latency it takes for something to happen, +and not the average. We can have a very fast scheduler that may +only have a large latency once in a while, but that would not +work well with Real-Time tasks. The wakeup_rt tracer was designed +to record the worst case wakeups of RT tasks. Non-RT tasks are +not recorded because the tracer only records one worst case and +tracing non-RT tasks that are unpredictable will overwrite the +worst case latency of RT tasks (just run the normal wakeup +tracer for a while to see that effect). + +Since this tracer only deals with RT tasks, we will run this +slightly differently than we did with the previous tracers. +Instead of performing an 'ls', we will run 'sleep 1' under +'chrt' which changes the priority of the task. +:: + + # echo 0 > options/function-trace + # echo wakeup_rt > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # chrt -f 5 sleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: wakeup + # + # tracer: wakeup_rt + # + # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep + <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 3d..3 5us : __schedule <-schedule + <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep + + +Running this on an idle system, we see that it only took 5 microseconds +to perform the task switch. Note, since the trace point in the schedule +is before the actual "switch", we stop the tracing when the recorded task +is about to schedule in. This may change if we add a new marker at the +end of the scheduler. + +Notice that the recorded task is 'sleep' with the PID of 2389 +and it has an rt_prio of 5. This priority is user-space priority +and not the internal kernel priority. The policy is 1 for +SCHED_FIFO and 2 for SCHED_RR. + +Note, that the trace data shows the internal priority (99 - rtprio). +:: + + <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep + +The 0:120:R means idle was running with a nice priority of 0 (120 - 120) +and in the running state 'R'. The sleep task was scheduled in with +2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94) +and it too is in the running state. + +Doing the same with chrt -r 5 and function-trace set. +:: + + echo 1 > options/function-trace + + # tracer: wakeup_rt + # + # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep + <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup + <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr + <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup + <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up + <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock + <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up + <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up + <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore + <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer + <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock + <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt + <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock + <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt + <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event + <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event + <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event + <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt + <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit + <idle>-0 3dN.2 9us : idle_cpu <-irq_exit + <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit + <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit + <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit + <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle + <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit + <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle + <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit + <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit + <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit + <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit + <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz + <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock + <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz + <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update + <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz + <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock + <idle>-0 3dN.1 15us : calc_load_nohz_stop <-tick_nohz_idle_exit + <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit + <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit + <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel + <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel + <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 + <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave + <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16 + <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer + <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram + <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event + <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event + <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event + <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel + <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore + <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit + <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward + <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward + <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 + <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns + <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns + <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 + <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave + <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns + <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns + <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns + <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event + <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event + <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event + <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns + <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore + <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit + <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks + <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle + <idle>-0 3.N.. 25us : schedule <-cpu_idle + <idle>-0 3.N.. 25us : __schedule <-preempt_schedule + <idle>-0 3.N.. 26us : add_preempt_count <-__schedule + <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule + <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch + <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch + <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule + <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq + <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule + <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task + <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task + <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt + <idle>-0 3d..3 29us : __schedule <-preempt_schedule + <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep + +This isn't that big of a trace, even with function tracing enabled, +so I included the entire trace. + +The interrupt went off while when the system was idle. Somewhere +before task_woken_rt() was called, the NEED_RESCHED flag was set, +this is indicated by the first occurrence of the 'N' flag. + +Latency tracing and events +-------------------------- +As function tracing can induce a much larger latency, but without +seeing what happens within the latency it is hard to know what +caused it. There is a middle ground, and that is with enabling +events. +:: + + # echo 0 > options/function-trace + # echo wakeup_rt > current_tracer + # echo 1 > events/enable + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # chrt -f 5 sleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: wakeup_rt + # + # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep + <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002 + <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8 + <idle>-0 2.N.2 2us : power_end: cpu_id=2 + <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2 + <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0 + <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000 + <idle>-0 2.N.2 5us : rcu_utilization: Start context switch + <idle>-0 2.N.2 5us : rcu_utilization: End context switch + <idle>-0 2d..3 6us : __schedule <-schedule + <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep + + +Hardware Latency Detector +------------------------- + +The hardware latency detector is executed by enabling the "hwlat" tracer. + +NOTE, this tracer will affect the performance of the system as it will +periodically make a CPU constantly busy with interrupts disabled. +:: + + # echo hwlat > current_tracer + # sleep 100 + # cat trace + # tracer: hwlat + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <...>-3638 [001] d... 19452.055471: #1 inner/outer(us): 12/14 ts:1499801089.066141940 + <...>-3638 [003] d... 19454.071354: #2 inner/outer(us): 11/9 ts:1499801091.082164365 + <...>-3638 [002] dn.. 19461.126852: #3 inner/outer(us): 12/9 ts:1499801098.138150062 + <...>-3638 [001] d... 19488.340960: #4 inner/outer(us): 8/12 ts:1499801125.354139633 + <...>-3638 [003] d... 19494.388553: #5 inner/outer(us): 8/12 ts:1499801131.402150961 + <...>-3638 [003] d... 19501.283419: #6 inner/outer(us): 0/12 ts:1499801138.297435289 nmi-total:4 nmi-count:1 + + +The above output is somewhat the same in the header. All events will have +interrupts disabled 'd'. Under the FUNCTION title there is: + + #1 + This is the count of events recorded that were greater than the + tracing_threshold (See below). + + inner/outer(us): 12/14 + + This shows two numbers as "inner latency" and "outer latency". The test + runs in a loop checking a timestamp twice. The latency detected within + the two timestamps is the "inner latency" and the latency detected + after the previous timestamp and the next timestamp in the loop is + the "outer latency". + + ts:1499801089.066141940 + + The absolute timestamp that the event happened. + + nmi-total:4 nmi-count:1 + + On architectures that support it, if an NMI comes in during the + test, the time spent in NMI is reported in "nmi-total" (in + microseconds). + + All architectures that have NMIs will show the "nmi-count" if an + NMI comes in during the test. + +hwlat files: + + tracing_threshold + This gets automatically set to "10" to represent 10 + microseconds. This is the threshold of latency that + needs to be detected before the trace will be recorded. + + Note, when hwlat tracer is finished (another tracer is + written into "current_tracer"), the original value for + tracing_threshold is placed back into this file. + + hwlat_detector/width + The length of time the test runs with interrupts disabled. + + hwlat_detector/window + The length of time of the window which the test + runs. That is, the test will run for "width" + microseconds per "window" microseconds + + tracing_cpumask + When the test is started. A kernel thread is created that + runs the test. This thread will alternate between CPUs + listed in the tracing_cpumask between each period + (one "window"). To limit the test to specific CPUs + set the mask in this file to only the CPUs that the test + should run on. + +function +-------- + +This tracer is the function tracer. Enabling the function tracer +can be done from the debug file system. Make sure the +ftrace_enabled is set; otherwise this tracer is a nop. +See the "ftrace_enabled" section below. +:: + + # sysctl kernel.ftrace_enabled=1 + # echo function > current_tracer + # echo 1 > tracing_on + # usleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: function + # + # entries-in-buffer/entries-written: 24799/24799 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write + bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock + bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify + bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify + bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify + bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock + bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock + bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify + [...] + + +Note: function tracer uses ring buffers to store the above +entries. The newest data may overwrite the oldest data. +Sometimes using echo to stop the trace is not sufficient because +the tracing could have overwritten the data that you wanted to +record. For this reason, it is sometimes better to disable +tracing directly from a program. This allows you to stop the +tracing at the point that you hit the part that you are +interested in. To disable the tracing directly from a C program, +something like following code snippet can be used:: + + int trace_fd; + [...] + int main(int argc, char *argv[]) { + [...] + trace_fd = open(tracing_file("tracing_on"), O_WRONLY); + [...] + if (condition_hit()) { + write(trace_fd, "0", 1); + } + [...] + } + + +Single thread tracing +--------------------- + +By writing into set_ftrace_pid you can trace a +single thread. For example:: + + # cat set_ftrace_pid + no pid + # echo 3111 > set_ftrace_pid + # cat set_ftrace_pid + 3111 + # echo function > current_tracer + # cat trace | head + # tracer: function + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return + yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range + yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel + yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel + yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll + yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll + # echo > set_ftrace_pid + # cat trace |head + # tracer: function + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + ##### CPU 3 buffer started #### + yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait + yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry + yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry + yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit + yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit + +If you want to trace a function when executing, you could use +something like this simple program. +:: + + #include <stdio.h> + #include <stdlib.h> + #include <sys/types.h> + #include <sys/stat.h> + #include <fcntl.h> + #include <unistd.h> + #include <string.h> + + #define _STR(x) #x + #define STR(x) _STR(x) + #define MAX_PATH 256 + + const char *find_tracefs(void) + { + static char tracefs[MAX_PATH+1]; + static int tracefs_found; + char type[100]; + FILE *fp; + + if (tracefs_found) + return tracefs; + + if ((fp = fopen("/proc/mounts","r")) == NULL) { + perror("/proc/mounts"); + return NULL; + } + + while (fscanf(fp, "%*s %" + STR(MAX_PATH) + "s %99s %*s %*d %*d\n", + tracefs, type) == 2) { + if (strcmp(type, "tracefs") == 0) + break; + } + fclose(fp); + + if (strcmp(type, "tracefs") != 0) { + fprintf(stderr, "tracefs not mounted"); + return NULL; + } + + strcat(tracefs, "/tracing/"); + tracefs_found = 1; + + return tracefs; + } + + const char *tracing_file(const char *file_name) + { + static char trace_file[MAX_PATH+1]; + snprintf(trace_file, MAX_PATH, "%s/%s", find_tracefs(), file_name); + return trace_file; + } + + int main (int argc, char **argv) + { + if (argc < 1) + exit(-1); + + if (fork() > 0) { + int fd, ffd; + char line[64]; + int s; + + ffd = open(tracing_file("current_tracer"), O_WRONLY); + if (ffd < 0) + exit(-1); + write(ffd, "nop", 3); + + fd = open(tracing_file("set_ftrace_pid"), O_WRONLY); + s = sprintf(line, "%d\n", getpid()); + write(fd, line, s); + + write(ffd, "function", 8); + + close(fd); + close(ffd); + + execvp(argv[1], argv+1); + } + + return 0; + } + +Or this simple script! +:: + + #!/bin/bash + + tracefs=`sed -ne 's/^tracefs \(.*\) tracefs.*/\1/p' /proc/mounts` + echo nop > $tracefs/tracing/current_tracer + echo 0 > $tracefs/tracing/tracing_on + echo $$ > $tracefs/tracing/set_ftrace_pid + echo function > $tracefs/tracing/current_tracer + echo 1 > $tracefs/tracing/tracing_on + exec "$@" + + +function graph tracer +--------------------------- + +This tracer is similar to the function tracer except that it +probes a function on its entry and its exit. This is done by +using a dynamically allocated stack of return addresses in each +task_struct. On function entry the tracer overwrites the return +address of each function traced to set a custom probe. Thus the +original return address is stored on the stack of return address +in the task_struct. + +Probing on both ends of a function leads to special features +such as: + +- measure of a function's time execution +- having a reliable call stack to draw function calls graph + +This tracer is useful in several situations: + +- you want to find the reason of a strange kernel behavior and + need to see what happens in detail on any areas (or specific + ones). + +- you are experiencing weird latencies but it's difficult to + find its origin. + +- you want to find quickly which path is taken by a specific + function + +- you just want to peek inside a working kernel and want to see + what happens there. + +:: + + # tracer: function_graph + # + # CPU DURATION FUNCTION CALLS + # | | | | | | | + + 0) | sys_open() { + 0) | do_sys_open() { + 0) | getname() { + 0) | kmem_cache_alloc() { + 0) 1.382 us | __might_sleep(); + 0) 2.478 us | } + 0) | strncpy_from_user() { + 0) | might_fault() { + 0) 1.389 us | __might_sleep(); + 0) 2.553 us | } + 0) 3.807 us | } + 0) 7.876 us | } + 0) | alloc_fd() { + 0) 0.668 us | _spin_lock(); + 0) 0.570 us | expand_files(); + 0) 0.586 us | _spin_unlock(); + + +There are several columns that can be dynamically +enabled/disabled. You can use every combination of options you +want, depending on your needs. + +- The cpu number on which the function executed is default + enabled. It is sometimes better to only trace one cpu (see + tracing_cpu_mask file) or you might sometimes see unordered + function calls while cpu tracing switch. + + - hide: echo nofuncgraph-cpu > trace_options + - show: echo funcgraph-cpu > trace_options + +- The duration (function's time of execution) is displayed on + the closing bracket line of a function or on the same line + than the current function in case of a leaf one. It is default + enabled. + + - hide: echo nofuncgraph-duration > trace_options + - show: echo funcgraph-duration > trace_options + +- The overhead field precedes the duration field in case of + reached duration thresholds. + + - hide: echo nofuncgraph-overhead > trace_options + - show: echo funcgraph-overhead > trace_options + - depends on: funcgraph-duration + + ie:: + + 3) # 1837.709 us | } /* __switch_to */ + 3) | finish_task_switch() { + 3) 0.313 us | _raw_spin_unlock_irq(); + 3) 3.177 us | } + 3) # 1889.063 us | } /* __schedule */ + 3) ! 140.417 us | } /* __schedule */ + 3) # 2034.948 us | } /* schedule */ + 3) * 33998.59 us | } /* schedule_preempt_disabled */ + + [...] + + 1) 0.260 us | msecs_to_jiffies(); + 1) 0.313 us | __rcu_read_unlock(); + 1) + 61.770 us | } + 1) + 64.479 us | } + 1) 0.313 us | rcu_bh_qs(); + 1) 0.313 us | __local_bh_enable(); + 1) ! 217.240 us | } + 1) 0.365 us | idle_cpu(); + 1) | rcu_irq_exit() { + 1) 0.417 us | rcu_eqs_enter_common.isra.47(); + 1) 3.125 us | } + 1) ! 227.812 us | } + 1) ! 457.395 us | } + 1) @ 119760.2 us | } + + [...] + + 2) | handle_IPI() { + 1) 6.979 us | } + 2) 0.417 us | scheduler_ipi(); + 1) 9.791 us | } + 1) + 12.917 us | } + 2) 3.490 us | } + 1) + 15.729 us | } + 1) + 18.542 us | } + 2) $ 3594274 us | } + +Flags:: + + + means that the function exceeded 10 usecs. + ! means that the function exceeded 100 usecs. + # means that the function exceeded 1000 usecs. + * means that the function exceeded 10 msecs. + @ means that the function exceeded 100 msecs. + $ means that the function exceeded 1 sec. + + +- The task/pid field displays the thread cmdline and pid which + executed the function. It is default disabled. + + - hide: echo nofuncgraph-proc > trace_options + - show: echo funcgraph-proc > trace_options + + ie:: + + # tracer: function_graph + # + # CPU TASK/PID DURATION FUNCTION CALLS + # | | | | | | | | | + 0) sh-4802 | | d_free() { + 0) sh-4802 | | call_rcu() { + 0) sh-4802 | | __call_rcu() { + 0) sh-4802 | 0.616 us | rcu_process_gp_end(); + 0) sh-4802 | 0.586 us | check_for_new_grace_period(); + 0) sh-4802 | 2.899 us | } + 0) sh-4802 | 4.040 us | } + 0) sh-4802 | 5.151 us | } + 0) sh-4802 | + 49.370 us | } + + +- The absolute time field is an absolute timestamp given by the + system clock since it started. A snapshot of this time is + given on each entry/exit of functions + + - hide: echo nofuncgraph-abstime > trace_options + - show: echo funcgraph-abstime > trace_options + + ie:: + + # + # TIME CPU DURATION FUNCTION CALLS + # | | | | | | | | + 360.774522 | 1) 0.541 us | } + 360.774522 | 1) 4.663 us | } + 360.774523 | 1) 0.541 us | __wake_up_bit(); + 360.774524 | 1) 6.796 us | } + 360.774524 | 1) 7.952 us | } + 360.774525 | 1) 9.063 us | } + 360.774525 | 1) 0.615 us | journal_mark_dirty(); + 360.774527 | 1) 0.578 us | __brelse(); + 360.774528 | 1) | reiserfs_prepare_for_journal() { + 360.774528 | 1) | unlock_buffer() { + 360.774529 | 1) | wake_up_bit() { + 360.774529 | 1) | bit_waitqueue() { + 360.774530 | 1) 0.594 us | __phys_addr(); + + +The function name is always displayed after the closing bracket +for a function if the start of that function is not in the +trace buffer. + +Display of the function name after the closing bracket may be +enabled for functions whose start is in the trace buffer, +allowing easier searching with grep for function durations. +It is default disabled. + + - hide: echo nofuncgraph-tail > trace_options + - show: echo funcgraph-tail > trace_options + + Example with nofuncgraph-tail (default):: + + 0) | putname() { + 0) | kmem_cache_free() { + 0) 0.518 us | __phys_addr(); + 0) 1.757 us | } + 0) 2.861 us | } + + Example with funcgraph-tail:: + + 0) | putname() { + 0) | kmem_cache_free() { + 0) 0.518 us | __phys_addr(); + 0) 1.757 us | } /* kmem_cache_free() */ + 0) 2.861 us | } /* putname() */ + +You can put some comments on specific functions by using +trace_printk() For example, if you want to put a comment inside +the __might_sleep() function, you just have to include +<linux/ftrace.h> and call trace_printk() inside __might_sleep():: + + trace_printk("I'm a comment!\n") + +will produce:: + + 1) | __might_sleep() { + 1) | /* I'm a comment! */ + 1) 1.449 us | } + + +You might find other useful features for this tracer in the +following "dynamic ftrace" section such as tracing only specific +functions or tasks. + +dynamic ftrace +-------------- + +If CONFIG_DYNAMIC_FTRACE is set, the system will run with +virtually no overhead when function tracing is disabled. The way +this works is the mcount function call (placed at the start of +every kernel function, produced by the -pg switch in gcc), +starts of pointing to a simple return. (Enabling FTRACE will +include the -pg switch in the compiling of the kernel.) + +At compile time every C file object is run through the +recordmcount program (located in the scripts directory). This +program will parse the ELF headers in the C object to find all +the locations in the .text section that call mcount. Starting +with gcc verson 4.6, the -mfentry has been added for x86, which +calls "__fentry__" instead of "mcount". Which is called before +the creation of the stack frame. + +Note, not all sections are traced. They may be prevented by either +a notrace, or blocked another way and all inline functions are not +traced. Check the "available_filter_functions" file to see what functions +can be traced. + +A section called "__mcount_loc" is created that holds +references to all the mcount/fentry call sites in the .text section. +The recordmcount program re-links this section back into the +original object. The final linking stage of the kernel will add all these +references into a single table. + +On boot up, before SMP is initialized, the dynamic ftrace code +scans this table and updates all the locations into nops. It +also records the locations, which are added to the +available_filter_functions list. Modules are processed as they +are loaded and before they are executed. When a module is +unloaded, it also removes its functions from the ftrace function +list. This is automatic in the module unload code, and the +module author does not need to worry about it. + +When tracing is enabled, the process of modifying the function +tracepoints is dependent on architecture. The old method is to use +kstop_machine to prevent races with the CPUs executing code being +modified (which can cause the CPU to do undesirable things, especially +if the modified code crosses cache (or page) boundaries), and the nops are +patched back to calls. But this time, they do not call mcount +(which is just a function stub). They now call into the ftrace +infrastructure. + +The new method of modifying the function tracepoints is to place +a breakpoint at the location to be modified, sync all CPUs, modify +the rest of the instruction not covered by the breakpoint. Sync +all CPUs again, and then remove the breakpoint with the finished +version to the ftrace call site. + +Some archs do not even need to monkey around with the synchronization, +and can just slap the new code on top of the old without any +problems with other CPUs executing it at the same time. + +One special side-effect to the recording of the functions being +traced is that we can now selectively choose which functions we +wish to trace and which ones we want the mcount calls to remain +as nops. + +Two files are used, one for enabling and one for disabling the +tracing of specified functions. They are: + + set_ftrace_filter + +and + + set_ftrace_notrace + +A list of available functions that you can add to these files is +listed in: + + available_filter_functions + +:: + + # cat available_filter_functions + put_prev_task_idle + kmem_cache_create + pick_next_task_rt + get_online_cpus + pick_next_task_fair + mutex_lock + [...] + +If I am only interested in sys_nanosleep and hrtimer_interrupt:: + + # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter + # echo function > current_tracer + # echo 1 > tracing_on + # usleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: function + # + # entries-in-buffer/entries-written: 5/5 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath + <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt + usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt + <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt + <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt + +To see which functions are being traced, you can cat the file: +:: + + # cat set_ftrace_filter + hrtimer_interrupt + sys_nanosleep + + +Perhaps this is not enough. The filters also allow glob(7) matching. + + ``<match>*`` + will match functions that begin with <match> + ``*<match>`` + will match functions that end with <match> + ``*<match>*`` + will match functions that have <match> in it + ``<match1>*<match2>`` + will match functions that begin with <match1> and end with <match2> + +.. note:: + It is better to use quotes to enclose the wild cards, + otherwise the shell may expand the parameters into names + of files in the local directory. + +:: + + # echo 'hrtimer_*' > set_ftrace_filter + +Produces:: + + # tracer: function + # + # entries-in-buffer/entries-written: 897/897 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit + <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel + <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer + <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit + <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 + <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt + <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter + <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem + +Notice that we lost the sys_nanosleep. +:: + + # cat set_ftrace_filter + hrtimer_run_queues + hrtimer_run_pending + hrtimer_init + hrtimer_cancel + hrtimer_try_to_cancel + hrtimer_forward + hrtimer_start + hrtimer_reprogram + hrtimer_force_reprogram + hrtimer_get_next_event + hrtimer_interrupt + hrtimer_nanosleep + hrtimer_wakeup + hrtimer_get_remaining + hrtimer_get_res + hrtimer_init_sleeper + + +This is because the '>' and '>>' act just like they do in bash. +To rewrite the filters, use '>' +To append to the filters, use '>>' + +To clear out a filter so that all functions will be recorded +again:: + + # echo > set_ftrace_filter + # cat set_ftrace_filter + # + +Again, now we want to append. + +:: + + # echo sys_nanosleep > set_ftrace_filter + # cat set_ftrace_filter + sys_nanosleep + # echo 'hrtimer_*' >> set_ftrace_filter + # cat set_ftrace_filter + hrtimer_run_queues + hrtimer_run_pending + hrtimer_init + hrtimer_cancel + hrtimer_try_to_cancel + hrtimer_forward + hrtimer_start + hrtimer_reprogram + hrtimer_force_reprogram + hrtimer_get_next_event + hrtimer_interrupt + sys_nanosleep + hrtimer_nanosleep + hrtimer_wakeup + hrtimer_get_remaining + hrtimer_get_res + hrtimer_init_sleeper + + +The set_ftrace_notrace prevents those functions from being +traced. +:: + + # echo '*preempt*' '*lock*' > set_ftrace_notrace + +Produces:: + + # tracer: function + # + # entries-in-buffer/entries-written: 39608/39608 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open + bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last + bash-1994 [000] .... 4342.324897: ima_file_check <-do_last + bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check + bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement + bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action + bash-1994 [000] .... 4342.324899: do_truncate <-do_last + bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate + bash-1994 [000] .... 4342.324899: notify_change <-do_truncate + bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change + bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time + bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time + +We can see that there's no more lock or preempt tracing. + + +Dynamic ftrace with the function graph tracer +--------------------------------------------- + +Although what has been explained above concerns both the +function tracer and the function-graph-tracer, there are some +special features only available in the function-graph tracer. + +If you want to trace only one function and all of its children, +you just have to echo its name into set_graph_function:: + + echo __do_fault > set_graph_function + +will produce the following "expanded" trace of the __do_fault() +function:: + + 0) | __do_fault() { + 0) | filemap_fault() { + 0) | find_lock_page() { + 0) 0.804 us | find_get_page(); + 0) | __might_sleep() { + 0) 1.329 us | } + 0) 3.904 us | } + 0) 4.979 us | } + 0) 0.653 us | _spin_lock(); + 0) 0.578 us | page_add_file_rmap(); + 0) 0.525 us | native_set_pte_at(); + 0) 0.585 us | _spin_unlock(); + 0) | unlock_page() { + 0) 0.541 us | page_waitqueue(); + 0) 0.639 us | __wake_up_bit(); + 0) 2.786 us | } + 0) + 14.237 us | } + 0) | __do_fault() { + 0) | filemap_fault() { + 0) | find_lock_page() { + 0) 0.698 us | find_get_page(); + 0) | __might_sleep() { + 0) 1.412 us | } + 0) 3.950 us | } + 0) 5.098 us | } + 0) 0.631 us | _spin_lock(); + 0) 0.571 us | page_add_file_rmap(); + 0) 0.526 us | native_set_pte_at(); + 0) 0.586 us | _spin_unlock(); + 0) | unlock_page() { + 0) 0.533 us | page_waitqueue(); + 0) 0.638 us | __wake_up_bit(); + 0) 2.793 us | } + 0) + 14.012 us | } + +You can also expand several functions at once:: + + echo sys_open > set_graph_function + echo sys_close >> set_graph_function + +Now if you want to go back to trace all functions you can clear +this special filter via:: + + echo > set_graph_function + + +ftrace_enabled +-------------- + +Note, the proc sysctl ftrace_enable is a big on/off switch for the +function tracer. By default it is enabled (when function tracing is +enabled in the kernel). If it is disabled, all function tracing is +disabled. This includes not only the function tracers for ftrace, but +also for any other uses (perf, kprobes, stack tracing, profiling, etc). + +Please disable this with care. + +This can be disable (and enabled) with:: + + sysctl kernel.ftrace_enabled=0 + sysctl kernel.ftrace_enabled=1 + + or + + echo 0 > /proc/sys/kernel/ftrace_enabled + echo 1 > /proc/sys/kernel/ftrace_enabled + + +Filter commands +--------------- + +A few commands are supported by the set_ftrace_filter interface. +Trace commands have the following format:: + + <function>:<command>:<parameter> + +The following commands are supported: + +- mod: + This command enables function filtering per module. The + parameter defines the module. For example, if only the write* + functions in the ext3 module are desired, run: + + echo 'write*:mod:ext3' > set_ftrace_filter + + This command interacts with the filter in the same way as + filtering based on function names. Thus, adding more functions + in a different module is accomplished by appending (>>) to the + filter file. Remove specific module functions by prepending + '!':: + + echo '!writeback*:mod:ext3' >> set_ftrace_filter + + Mod command supports module globbing. Disable tracing for all + functions except a specific module:: + + echo '!*:mod:!ext3' >> set_ftrace_filter + + Disable tracing for all modules, but still trace kernel:: + + echo '!*:mod:*' >> set_ftrace_filter + + Enable filter only for kernel:: + + echo '*write*:mod:!*' >> set_ftrace_filter + + Enable filter for module globbing:: + + echo '*write*:mod:*snd*' >> set_ftrace_filter + +- traceon/traceoff: + These commands turn tracing on and off when the specified + functions are hit. The parameter determines how many times the + tracing system is turned on and off. If unspecified, there is + no limit. For example, to disable tracing when a schedule bug + is hit the first 5 times, run:: + + echo '__schedule_bug:traceoff:5' > set_ftrace_filter + + To always disable tracing when __schedule_bug is hit:: + + echo '__schedule_bug:traceoff' > set_ftrace_filter + + These commands are cumulative whether or not they are appended + to set_ftrace_filter. To remove a command, prepend it by '!' + and drop the parameter:: + + echo '!__schedule_bug:traceoff:0' > set_ftrace_filter + + The above removes the traceoff command for __schedule_bug + that have a counter. To remove commands without counters:: + + echo '!__schedule_bug:traceoff' > set_ftrace_filter + +- snapshot: + Will cause a snapshot to be triggered when the function is hit. + :: + + echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter + + To only snapshot once: + :: + + echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter + + To remove the above commands:: + + echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter + echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter + +- enable_event/disable_event: + These commands can enable or disable a trace event. Note, because + function tracing callbacks are very sensitive, when these commands + are registered, the trace point is activated, but disabled in + a "soft" mode. That is, the tracepoint will be called, but + just will not be traced. The event tracepoint stays in this mode + as long as there's a command that triggers it. + :: + + echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \ + set_ftrace_filter + + The format is:: + + <function>:enable_event:<system>:<event>[:count] + <function>:disable_event:<system>:<event>[:count] + + To remove the events commands:: + + echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \ + set_ftrace_filter + echo '!schedule:disable_event:sched:sched_switch' > \ + set_ftrace_filter + +- dump: + When the function is hit, it will dump the contents of the ftrace + ring buffer to the console. This is useful if you need to debug + something, and want to dump the trace when a certain function + is hit. Perhaps its a function that is called before a tripple + fault happens and does not allow you to get a regular dump. + +- cpudump: + When the function is hit, it will dump the contents of the ftrace + ring buffer for the current CPU to the console. Unlike the "dump" + command, it only prints out the contents of the ring buffer for the + CPU that executed the function that triggered the dump. + +trace_pipe +---------- + +The trace_pipe outputs the same content as the trace file, but +the effect on the tracing is different. Every read from +trace_pipe is consumed. This means that subsequent reads will be +different. The trace is live. +:: + + # echo function > current_tracer + # cat trace_pipe > /tmp/trace.out & + [1] 4153 + # echo 1 > tracing_on + # usleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: function + # + # entries-in-buffer/entries-written: 0/0 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + + # + # cat /tmp/trace.out + bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write + bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock + bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify + bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify + bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify + bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock + bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock + bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify + bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath + + +Note, reading the trace_pipe file will block until more input is +added. + +trace entries +------------- + +Having too much or not enough data can be troublesome in +diagnosing an issue in the kernel. The file buffer_size_kb is +used to modify the size of the internal trace buffers. The +number listed is the number of entries that can be recorded per +CPU. To know the full size, multiply the number of possible CPUs +with the number of entries. +:: + + # cat buffer_size_kb + 1408 (units kilobytes) + +Or simply read buffer_total_size_kb +:: + + # cat buffer_total_size_kb + 5632 + +To modify the buffer, simple echo in a number (in 1024 byte segments). +:: + + # echo 10000 > buffer_size_kb + # cat buffer_size_kb + 10000 (units kilobytes) + +It will try to allocate as much as possible. If you allocate too +much, it can cause Out-Of-Memory to trigger. +:: + + # echo 1000000000000 > buffer_size_kb + -bash: echo: write error: Cannot allocate memory + # cat buffer_size_kb + 85 + +The per_cpu buffers can be changed individually as well: +:: + + # echo 10000 > per_cpu/cpu0/buffer_size_kb + # echo 100 > per_cpu/cpu1/buffer_size_kb + +When the per_cpu buffers are not the same, the buffer_size_kb +at the top level will just show an X +:: + + # cat buffer_size_kb + X + +This is where the buffer_total_size_kb is useful: +:: + + # cat buffer_total_size_kb + 12916 + +Writing to the top level buffer_size_kb will reset all the buffers +to be the same again. + +Snapshot +-------- +CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature +available to all non latency tracers. (Latency tracers which +record max latency, such as "irqsoff" or "wakeup", can't use +this feature, since those are already using the snapshot +mechanism internally.) + +Snapshot preserves a current trace buffer at a particular point +in time without stopping tracing. Ftrace swaps the current +buffer with a spare buffer, and tracing continues in the new +current (=previous spare) buffer. + +The following tracefs files in "tracing" are related to this +feature: + + snapshot: + + This is used to take a snapshot and to read the output + of the snapshot. Echo 1 into this file to allocate a + spare buffer and to take a snapshot (swap), then read + the snapshot from this file in the same format as + "trace" (described above in the section "The File + System"). Both reads snapshot and tracing are executable + in parallel. When the spare buffer is allocated, echoing + 0 frees it, and echoing else (positive) values clear the + snapshot contents. + More details are shown in the table below. + + +--------------+------------+------------+------------+ + |status\\input | 0 | 1 | else | + +==============+============+============+============+ + |not allocated |(do nothing)| alloc+swap |(do nothing)| + +--------------+------------+------------+------------+ + |allocated | free | swap | clear | + +--------------+------------+------------+------------+ + +Here is an example of using the snapshot feature. +:: + + # echo 1 > events/sched/enable + # echo 1 > snapshot + # cat snapshot + # tracer: nop + # + # entries-in-buffer/entries-written: 71/71 #P:8 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <idle>-0 [005] d... 2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120 + sleep-2242 [005] d... 2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120 + [...] + <idle>-0 [002] d... 2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120 + + # cat trace + # tracer: nop + # + # entries-in-buffer/entries-written: 77/77 #P:8 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <idle>-0 [007] d... 2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120 + snapshot-test-2-2229 [002] d... 2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120 + [...] + + +If you try to use this snapshot feature when current tracer is +one of the latency tracers, you will get the following results. +:: + + # echo wakeup > current_tracer + # echo 1 > snapshot + bash: echo: write error: Device or resource busy + # cat snapshot + cat: snapshot: Device or resource busy + + +Instances +--------- +In the tracefs tracing directory is a directory called "instances". +This directory can have new directories created inside of it using +mkdir, and removing directories with rmdir. The directory created +with mkdir in this directory will already contain files and other +directories after it is created. +:: + + # mkdir instances/foo + # ls instances/foo + buffer_size_kb buffer_total_size_kb events free_buffer per_cpu + set_event snapshot trace trace_clock trace_marker trace_options + trace_pipe tracing_on + +As you can see, the new directory looks similar to the tracing directory +itself. In fact, it is very similar, except that the buffer and +events are agnostic from the main director, or from any other +instances that are created. + +The files in the new directory work just like the files with the +same name in the tracing directory except the buffer that is used +is a separate and new buffer. The files affect that buffer but do not +affect the main buffer with the exception of trace_options. Currently, +the trace_options affect all instances and the top level buffer +the same, but this may change in future releases. That is, options +may become specific to the instance they reside in. + +Notice that none of the function tracer files are there, nor is +current_tracer and available_tracers. This is because the buffers +can currently only have events enabled for them. +:: + + # mkdir instances/foo + # mkdir instances/bar + # mkdir instances/zoot + # echo 100000 > buffer_size_kb + # echo 1000 > instances/foo/buffer_size_kb + # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb + # echo function > current_trace + # echo 1 > instances/foo/events/sched/sched_wakeup/enable + # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable + # echo 1 > instances/foo/events/sched/sched_switch/enable + # echo 1 > instances/bar/events/irq/enable + # echo 1 > instances/zoot/events/syscalls/enable + # cat trace_pipe + CPU:2 [LOST 11745 EVENTS] + bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist + bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave + bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist + bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist + bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock + bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype + bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist + bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist + bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics + bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics + bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process + [...] + + # cat instances/foo/trace_pipe + bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 + bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 + <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003 + <idle>-0 [003] d..3 136.676909: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=9 next_prio=120 + rcu_preempt-9 [003] d..3 136.676916: sched_switch: prev_comm=rcu_preempt prev_pid=9 prev_prio=120 prev_state=S ==> next_comm=swapper/3 next_pid=0 next_prio=120 + bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 + bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 + bash-1998 [000] d..3 136.677018: sched_switch: prev_comm=bash prev_pid=1998 prev_prio=120 prev_state=R+ ==> next_comm=kworker/0:1 next_pid=59 next_prio=120 + kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001 + kworker/0:1-59 [000] d..3 136.677025: sched_switch: prev_comm=kworker/0:1 prev_pid=59 prev_prio=120 prev_state=S ==> next_comm=bash next_pid=1998 next_prio=120 + [...] + + # cat instances/bar/trace_pipe + migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX] + <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX] + bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER] + bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU] + bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER] + bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER] + bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU] + bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU] + sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4 + sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled + sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0 + sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled + [...] + + # cat instances/zoot/trace + # tracer: nop + # + # entries-in-buffer/entries-written: 18996/18996 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1998 [000] d... 140.733501: sys_write -> 0x2 + bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1) + bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1 + bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0) + bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1 + bash-1998 [000] d... 140.733510: sys_close(fd: a) + bash-1998 [000] d... 140.733510: sys_close -> 0x0 + bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8) + bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0 + bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8) + bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0 + +You can see that the trace of the top most trace buffer shows only +the function tracing. The foo instance displays wakeups and task +switches. + +To remove the instances, simply delete their directories: +:: + + # rmdir instances/foo + # rmdir instances/bar + # rmdir instances/zoot + +Note, if a process has a trace file open in one of the instance +directories, the rmdir will fail with EBUSY. + + +Stack trace +----------- +Since the kernel has a fixed sized stack, it is important not to +waste it in functions. A kernel developer must be conscience of +what they allocate on the stack. If they add too much, the system +can be in danger of a stack overflow, and corruption will occur, +usually leading to a system panic. + +There are some tools that check this, usually with interrupts +periodically checking usage. But if you can perform a check +at every function call that will become very useful. As ftrace provides +a function tracer, it makes it convenient to check the stack size +at every function call. This is enabled via the stack tracer. + +CONFIG_STACK_TRACER enables the ftrace stack tracing functionality. +To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled. +:: + + # echo 1 > /proc/sys/kernel/stack_tracer_enabled + +You can also enable it from the kernel command line to trace +the stack size of the kernel during boot up, by adding "stacktrace" +to the kernel command line parameter. + +After running it for a few minutes, the output looks like: +:: + + # cat stack_max_size + 2928 + + # cat stack_trace + Depth Size Location (18 entries) + ----- ---- -------- + 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac + 1) 2704 160 find_busiest_group+0x31/0x1f1 + 2) 2544 256 load_balance+0xd9/0x662 + 3) 2288 80 idle_balance+0xbb/0x130 + 4) 2208 128 __schedule+0x26e/0x5b9 + 5) 2080 16 schedule+0x64/0x66 + 6) 2064 128 schedule_timeout+0x34/0xe0 + 7) 1936 112 wait_for_common+0x97/0xf1 + 8) 1824 16 wait_for_completion+0x1d/0x1f + 9) 1808 128 flush_work+0xfe/0x119 + 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20 + 11) 1664 48 input_available_p+0x1d/0x5c + 12) 1616 48 n_tty_poll+0x6d/0x134 + 13) 1568 64 tty_poll+0x64/0x7f + 14) 1504 880 do_select+0x31e/0x511 + 15) 624 400 core_sys_select+0x177/0x216 + 16) 224 96 sys_select+0x91/0xb9 + 17) 128 128 system_call_fastpath+0x16/0x1b + +Note, if -mfentry is being used by gcc, functions get traced before +they set up the stack frame. This means that leaf level functions +are not tested by the stack tracer when -mfentry is used. + +Currently, -mfentry is used by gcc 4.6.0 and above on x86 only. + +More +---- +More details can be found in the source code, in the `kernel/trace/*.c` files. diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt deleted file mode 100644 index d4601df6e72e..000000000000 --- a/Documentation/trace/ftrace.txt +++ /dev/null @@ -1,3220 +0,0 @@ - ftrace - Function Tracer - ======================== - -Copyright 2008 Red Hat Inc. - Author: Steven Rostedt <srostedt@redhat.com> - License: The GNU Free Documentation License, Version 1.2 - (dual licensed under the GPL v2) -Original Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton, - John Kacur, and David Teigland. -Written for: 2.6.28-rc2 -Updated for: 3.10 -Updated for: 4.13 - Copyright 2017 VMware Inc. Steven Rostedt - -Introduction ------------- - -Ftrace is an internal tracer designed to help out developers and -designers of systems to find what is going on inside the kernel. -It can be used for debugging or analyzing latencies and -performance issues that take place outside of user-space. - -Although ftrace is typically considered the function tracer, it -is really a frame work of several assorted tracing utilities. -There's latency tracing to examine what occurs between interrupts -disabled and enabled, as well as for preemption and from a time -a task is woken to the task is actually scheduled in. - -One of the most common uses of ftrace is the event tracing. -Through out the kernel is hundreds of static event points that -can be enabled via the tracefs file system to see what is -going on in certain parts of the kernel. - -See events.txt for more information. - - -Implementation Details ----------------------- - -See ftrace-design.txt for details for arch porters and such. - - -The File System ---------------- - -Ftrace uses the tracefs file system to hold the control files as -well as the files to display output. - -When tracefs is configured into the kernel (which selecting any ftrace -option will do) the directory /sys/kernel/tracing will be created. To mount -this directory, you can add to your /etc/fstab file: - - tracefs /sys/kernel/tracing tracefs defaults 0 0 - -Or you can mount it at run time with: - - mount -t tracefs nodev /sys/kernel/tracing - -For quicker access to that directory you may want to make a soft link to -it: - - ln -s /sys/kernel/tracing /tracing - - *** NOTICE *** - -Before 4.1, all ftrace tracing control files were within the debugfs -file system, which is typically located at /sys/kernel/debug/tracing. -For backward compatibility, when mounting the debugfs file system, -the tracefs file system will be automatically mounted at: - - /sys/kernel/debug/tracing - -All files located in the tracefs file system will be located in that -debugfs file system directory as well. - - *** NOTICE *** - -Any selected ftrace option will also create the tracefs file system. -The rest of the document will assume that you are in the ftrace directory -(cd /sys/kernel/tracing) and will only concentrate on the files within that -directory and not distract from the content with the extended -"/sys/kernel/tracing" path name. - -That's it! (assuming that you have ftrace configured into your kernel) - -After mounting tracefs you will have access to the control and output files -of ftrace. Here is a list of some of the key files: - - - Note: all time values are in microseconds. - - current_tracer: - - This is used to set or display the current tracer - that is configured. - - available_tracers: - - This holds the different types of tracers that - have been compiled into the kernel. The - tracers listed here can be configured by - echoing their name into current_tracer. - - tracing_on: - - This sets or displays whether writing to the trace - ring buffer is enabled. Echo 0 into this file to disable - the tracer or 1 to enable it. Note, this only disables - writing to the ring buffer, the tracing overhead may - still be occurring. - - The kernel function tracing_off() can be used within the - kernel to disable writing to the ring buffer, which will - set this file to "0". User space can re-enable tracing by - echoing "1" into the file. - - Note, the function and event trigger "traceoff" will also - set this file to zero and stop tracing. Which can also - be re-enabled by user space using this file. - - trace: - - This file holds the output of the trace in a human - readable format (described below). Note, tracing is temporarily - disabled while this file is being read (opened). - - trace_pipe: - - The output is the same as the "trace" file but this - file is meant to be streamed with live tracing. - Reads from this file will block until new data is - retrieved. Unlike the "trace" file, this file is a - consumer. This means reading from this file causes - sequential reads to display more current data. Once - data is read from this file, it is consumed, and - will not be read again with a sequential read. The - "trace" file is static, and if the tracer is not - adding more data, it will display the same - information every time it is read. This file will not - disable tracing while being read. - - trace_options: - - This file lets the user control the amount of data - that is displayed in one of the above output - files. Options also exist to modify how a tracer - or events work (stack traces, timestamps, etc). - - options: - - This is a directory that has a file for every available - trace option (also in trace_options). Options may also be set - or cleared by writing a "1" or "0" respectively into the - corresponding file with the option name. - - tracing_max_latency: - - Some of the tracers record the max latency. - For example, the maximum time that interrupts are disabled. - The maximum time is saved in this file. The max trace will also be - stored, and displayed by "trace". A new max trace will only be - recorded if the latency is greater than the value in this file - (in microseconds). - - By echoing in a time into this file, no latency will be recorded - unless it is greater than the time in this file. - - tracing_thresh: - - Some latency tracers will record a trace whenever the - latency is greater than the number in this file. - Only active when the file contains a number greater than 0. - (in microseconds) - - buffer_size_kb: - - This sets or displays the number of kilobytes each CPU - buffer holds. By default, the trace buffers are the same size - for each CPU. The displayed number is the size of the - CPU buffer and not total size of all buffers. The - trace buffers are allocated in pages (blocks of memory - that the kernel uses for allocation, usually 4 KB in size). - If the last page allocated has room for more bytes - than requested, the rest of the page will be used, - making the actual allocation bigger than requested or shown. - ( Note, the size may not be a multiple of the page size - due to buffer management meta-data. ) - - Buffer sizes for individual CPUs may vary - (see "per_cpu/cpu0/buffer_size_kb" below), and if they do - this file will show "X". - - buffer_total_size_kb: - - This displays the total combined size of all the trace buffers. - - free_buffer: - - If a process is performing tracing, and the ring buffer should be - shrunk "freed" when the process is finished, even if it were to be - killed by a signal, this file can be used for that purpose. On close - of this file, the ring buffer will be resized to its minimum size. - Having a process that is tracing also open this file, when the process - exits its file descriptor for this file will be closed, and in doing so, - the ring buffer will be "freed". - - It may also stop tracing if disable_on_free option is set. - - tracing_cpumask: - - This is a mask that lets the user only trace on specified CPUs. - The format is a hex string representing the CPUs. - - set_ftrace_filter: - - When dynamic ftrace is configured in (see the - section below "dynamic ftrace"), the code is dynamically - modified (code text rewrite) to disable calling of the - function profiler (mcount). This lets tracing be configured - in with practically no overhead in performance. This also - has a side effect of enabling or disabling specific functions - to be traced. Echoing names of functions into this file - will limit the trace to only those functions. - - The functions listed in "available_filter_functions" are what - can be written into this file. - - This interface also allows for commands to be used. See the - "Filter commands" section for more details. - - set_ftrace_notrace: - - This has an effect opposite to that of - set_ftrace_filter. Any function that is added here will not - be traced. If a function exists in both set_ftrace_filter - and set_ftrace_notrace, the function will _not_ be traced. - - set_ftrace_pid: - - Have the function tracer only trace the threads whose PID are - listed in this file. - - If the "function-fork" option is set, then when a task whose - PID is listed in this file forks, the child's PID will - automatically be added to this file, and the child will be - traced by the function tracer as well. This option will also - cause PIDs of tasks that exit to be removed from the file. - - set_event_pid: - - Have the events only trace a task with a PID listed in this file. - Note, sched_switch and sched_wake_up will also trace events - listed in this file. - - To have the PIDs of children of tasks with their PID in this file - added on fork, enable the "event-fork" option. That option will also - cause the PIDs of tasks to be removed from this file when the task - exits. - - set_graph_function: - - Functions listed in this file will cause the function graph - tracer to only trace these functions and the functions that - they call. (See the section "dynamic ftrace" for more details). - - set_graph_notrace: - - Similar to set_graph_function, but will disable function graph - tracing when the function is hit until it exits the function. - This makes it possible to ignore tracing functions that are called - by a specific function. - - available_filter_functions: - - This lists the functions that ftrace has processed and can trace. - These are the function names that you can pass to - "set_ftrace_filter" or "set_ftrace_notrace". - (See the section "dynamic ftrace" below for more details.) - - dyn_ftrace_total_info: - - This file is for debugging purposes. The number of functions that - have been converted to nops and are available to be traced. - - enabled_functions: - - This file is more for debugging ftrace, but can also be useful - in seeing if any function has a callback attached to it. - Not only does the trace infrastructure use ftrace function - trace utility, but other subsystems might too. This file - displays all functions that have a callback attached to them - as well as the number of callbacks that have been attached. - Note, a callback may also call multiple functions which will - not be listed in this count. - - If the callback registered to be traced by a function with - the "save regs" attribute (thus even more overhead), a 'R' - will be displayed on the same line as the function that - is returning registers. - - If the callback registered to be traced by a function with - the "ip modify" attribute (thus the regs->ip can be changed), - an 'I' will be displayed on the same line as the function that - can be overridden. - - If the architecture supports it, it will also show what callback - is being directly called by the function. If the count is greater - than 1 it most likely will be ftrace_ops_list_func(). - - If the callback of the function jumps to a trampoline that is - specific to a the callback and not the standard trampoline, - its address will be printed as well as the function that the - trampoline calls. - - function_profile_enabled: - - When set it will enable all functions with either the function - tracer, or if configured, the function graph tracer. It will - keep a histogram of the number of functions that were called - and if the function graph tracer was configured, it will also keep - track of the time spent in those functions. The histogram - content can be displayed in the files: - - trace_stats/function<cpu> ( function0, function1, etc). - - trace_stats: - - A directory that holds different tracing stats. - - kprobe_events: - - Enable dynamic trace points. See kprobetrace.txt. - - kprobe_profile: - - Dynamic trace points stats. See kprobetrace.txt. - - max_graph_depth: - - Used with the function graph tracer. This is the max depth - it will trace into a function. Setting this to a value of - one will show only the first kernel function that is called - from user space. - - printk_formats: - - This is for tools that read the raw format files. If an event in - the ring buffer references a string, only a pointer to the string - is recorded into the buffer and not the string itself. This prevents - tools from knowing what that string was. This file displays the string - and address for the string allowing tools to map the pointers to what - the strings were. - - saved_cmdlines: - - Only the pid of the task is recorded in a trace event unless - the event specifically saves the task comm as well. Ftrace - makes a cache of pid mappings to comms to try to display - comms for events. If a pid for a comm is not listed, then - "<...>" is displayed in the output. - - If the option "record-cmd" is set to "0", then comms of tasks - will not be saved during recording. By default, it is enabled. - - saved_cmdlines_size: - - By default, 128 comms are saved (see "saved_cmdlines" above). To - increase or decrease the amount of comms that are cached, echo - in a the number of comms to cache, into this file. - - saved_tgids: - - If the option "record-tgid" is set, on each scheduling context switch - the Task Group ID of a task is saved in a table mapping the PID of - the thread to its TGID. By default, the "record-tgid" option is - disabled. - - snapshot: - - This displays the "snapshot" buffer and also lets the user - take a snapshot of the current running trace. - See the "Snapshot" section below for more details. - - stack_max_size: - - When the stack tracer is activated, this will display the - maximum stack size it has encountered. - See the "Stack Trace" section below. - - stack_trace: - - This displays the stack back trace of the largest stack - that was encountered when the stack tracer is activated. - See the "Stack Trace" section below. - - stack_trace_filter: - - This is similar to "set_ftrace_filter" but it limits what - functions the stack tracer will check. - - trace_clock: - - Whenever an event is recorded into the ring buffer, a - "timestamp" is added. This stamp comes from a specified - clock. By default, ftrace uses the "local" clock. This - clock is very fast and strictly per cpu, but on some - systems it may not be monotonic with respect to other - CPUs. In other words, the local clocks may not be in sync - with local clocks on other CPUs. - - Usual clocks for tracing: - - # cat trace_clock - [local] global counter x86-tsc - - The clock with the square brackets around it is the one - in effect. - - local: Default clock, but may not be in sync across CPUs - - global: This clock is in sync with all CPUs but may - be a bit slower than the local clock. - - counter: This is not a clock at all, but literally an atomic - counter. It counts up one by one, but is in sync - with all CPUs. This is useful when you need to - know exactly the order events occurred with respect to - each other on different CPUs. - - uptime: This uses the jiffies counter and the time stamp - is relative to the time since boot up. - - perf: This makes ftrace use the same clock that perf uses. - Eventually perf will be able to read ftrace buffers - and this will help out in interleaving the data. - - x86-tsc: Architectures may define their own clocks. For - example, x86 uses its own TSC cycle clock here. - - ppc-tb: This uses the powerpc timebase register value. - This is in sync across CPUs and can also be used - to correlate events across hypervisor/guest if - tb_offset is known. - - mono: This uses the fast monotonic clock (CLOCK_MONOTONIC) - which is monotonic and is subject to NTP rate adjustments. - - mono_raw: - This is the raw monotonic clock (CLOCK_MONOTONIC_RAW) - which is montonic but is not subject to any rate adjustments - and ticks at the same rate as the hardware clocksource. - - boot: This is the boot clock (CLOCK_BOOTTIME) and is based on the - fast monotonic clock, but also accounts for time spent in - suspend. Since the clock access is designed for use in - tracing in the suspend path, some side effects are possible - if clock is accessed after the suspend time is accounted before - the fast mono clock is updated. In this case, the clock update - appears to happen slightly sooner than it normally would have. - Also on 32-bit systems, it's possible that the 64-bit boot offset - sees a partial update. These effects are rare and post - processing should be able to handle them. See comments in the - ktime_get_boot_fast_ns() function for more information. - - To set a clock, simply echo the clock name into this file. - - echo global > trace_clock - - trace_marker: - - This is a very useful file for synchronizing user space - with events happening in the kernel. Writing strings into - this file will be written into the ftrace buffer. - - It is useful in applications to open this file at the start - of the application and just reference the file descriptor - for the file. - - void trace_write(const char *fmt, ...) - { - va_list ap; - char buf[256]; - int n; - - if (trace_fd < 0) - return; - - va_start(ap, fmt); - n = vsnprintf(buf, 256, fmt, ap); - va_end(ap); - - write(trace_fd, buf, n); - } - - start: - - trace_fd = open("trace_marker", WR_ONLY); - - trace_marker_raw: - - This is similar to trace_marker above, but is meant for for binary data - to be written to it, where a tool can be used to parse the data - from trace_pipe_raw. - - uprobe_events: - - Add dynamic tracepoints in programs. - See uprobetracer.txt - - uprobe_profile: - - Uprobe statistics. See uprobetrace.txt - - instances: - - This is a way to make multiple trace buffers where different - events can be recorded in different buffers. - See "Instances" section below. - - events: - - This is the trace event directory. It holds event tracepoints - (also known as static tracepoints) that have been compiled - into the kernel. It shows what event tracepoints exist - and how they are grouped by system. There are "enable" - files at various levels that can enable the tracepoints - when a "1" is written to them. - - See events.txt for more information. - - set_event: - - By echoing in the event into this file, will enable that event. - - See events.txt for more information. - - available_events: - - A list of events that can be enabled in tracing. - - See events.txt for more information. - - hwlat_detector: - - Directory for the Hardware Latency Detector. - See "Hardware Latency Detector" section below. - - per_cpu: - - This is a directory that contains the trace per_cpu information. - - per_cpu/cpu0/buffer_size_kb: - - The ftrace buffer is defined per_cpu. That is, there's a separate - buffer for each CPU to allow writes to be done atomically, - and free from cache bouncing. These buffers may have different - size buffers. This file is similar to the buffer_size_kb - file, but it only displays or sets the buffer size for the - specific CPU. (here cpu0). - - per_cpu/cpu0/trace: - - This is similar to the "trace" file, but it will only display - the data specific for the CPU. If written to, it only clears - the specific CPU buffer. - - per_cpu/cpu0/trace_pipe - - This is similar to the "trace_pipe" file, and is a consuming - read, but it will only display (and consume) the data specific - for the CPU. - - per_cpu/cpu0/trace_pipe_raw - - For tools that can parse the ftrace ring buffer binary format, - the trace_pipe_raw file can be used to extract the data - from the ring buffer directly. With the use of the splice() - system call, the buffer data can be quickly transferred to - a file or to the network where a server is collecting the - data. - - Like trace_pipe, this is a consuming reader, where multiple - reads will always produce different data. - - per_cpu/cpu0/snapshot: - - This is similar to the main "snapshot" file, but will only - snapshot the current CPU (if supported). It only displays - the content of the snapshot for a given CPU, and if - written to, only clears this CPU buffer. - - per_cpu/cpu0/snapshot_raw: - - Similar to the trace_pipe_raw, but will read the binary format - from the snapshot buffer for the given CPU. - - per_cpu/cpu0/stats: - - This displays certain stats about the ring buffer: - - entries: The number of events that are still in the buffer. - - overrun: The number of lost events due to overwriting when - the buffer was full. - - commit overrun: Should always be zero. - This gets set if so many events happened within a nested - event (ring buffer is re-entrant), that it fills the - buffer and starts dropping events. - - bytes: Bytes actually read (not overwritten). - - oldest event ts: The oldest timestamp in the buffer - - now ts: The current timestamp - - dropped events: Events lost due to overwrite option being off. - - read events: The number of events read. - -The Tracers ------------ - -Here is the list of current tracers that may be configured. - - "function" - - Function call tracer to trace all kernel functions. - - "function_graph" - - Similar to the function tracer except that the - function tracer probes the functions on their entry - whereas the function graph tracer traces on both entry - and exit of the functions. It then provides the ability - to draw a graph of function calls similar to C code - source. - - "blk" - - The block tracer. The tracer used by the blktrace user - application. - - "hwlat" - - The Hardware Latency tracer is used to detect if the hardware - produces any latency. See "Hardware Latency Detector" section - below. - - "irqsoff" - - Traces the areas that disable interrupts and saves - the trace with the longest max latency. - See tracing_max_latency. When a new max is recorded, - it replaces the old trace. It is best to view this - trace with the latency-format option enabled, which - happens automatically when the tracer is selected. - - "preemptoff" - - Similar to irqsoff but traces and records the amount of - time for which preemption is disabled. - - "preemptirqsoff" - - Similar to irqsoff and preemptoff, but traces and - records the largest time for which irqs and/or preemption - is disabled. - - "wakeup" - - Traces and records the max latency that it takes for - the highest priority task to get scheduled after - it has been woken up. - Traces all tasks as an average developer would expect. - - "wakeup_rt" - - Traces and records the max latency that it takes for just - RT tasks (as the current "wakeup" does). This is useful - for those interested in wake up timings of RT tasks. - - "wakeup_dl" - - Traces and records the max latency that it takes for - a SCHED_DEADLINE task to be woken (as the "wakeup" and - "wakeup_rt" does). - - "mmiotrace" - - A special tracer that is used to trace binary module. - It will trace all the calls that a module makes to the - hardware. Everything it writes and reads from the I/O - as well. - - "branch" - - This tracer can be configured when tracing likely/unlikely - calls within the kernel. It will trace when a likely and - unlikely branch is hit and if it was correct in its prediction - of being correct. - - "nop" - - This is the "trace nothing" tracer. To remove all - tracers from tracing simply echo "nop" into - current_tracer. - - -Examples of using the tracer ----------------------------- - -Here are typical examples of using the tracers when controlling -them only with the tracefs interface (without using any -user-land utilities). - -Output format: --------------- - -Here is an example of the output format of the file "trace" - - -------- -# tracer: function -# -# entries-in-buffer/entries-written: 140080/250280 #P:4 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath - bash-1977 [000] .... 17284.993653: __close_fd <-sys_close - bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd - sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify - bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock - bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd - bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock - bash-1977 [000] .... 17284.993657: filp_close <-__close_fd - bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close - sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath - -------- - -A header is printed with the tracer name that is represented by -the trace. In this case the tracer is "function". Then it shows the -number of events in the buffer as well as the total number of entries -that were written. The difference is the number of entries that were -lost due to the buffer filling up (250280 - 140080 = 110200 events -lost). - -The header explains the content of the events. Task name "bash", the task -PID "1977", the CPU that it was running on "000", the latency format -(explained below), the timestamp in <secs>.<usecs> format, the -function name that was traced "sys_close" and the parent function that -called this function "system_call_fastpath". The timestamp is the time -at which the function was entered. - -Latency trace format --------------------- - -When the latency-format option is enabled or when one of the latency -tracers is set, the trace file gives somewhat more information to see -why a latency happened. Here is a typical trace. - -# tracer: irqsoff -# -# irqsoff latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0) -# ----------------- -# => started at: __lock_task_sighand -# => ended at: _raw_spin_unlock_irqrestore -# -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand - ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore - ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore - ps-6143 2d..1 306us : <stack trace> - => trace_hardirqs_on_caller - => trace_hardirqs_on - => _raw_spin_unlock_irqrestore - => do_task_stat - => proc_tgid_stat - => proc_single_show - => seq_read - => vfs_read - => sys_read - => system_call_fastpath - - -This shows that the current tracer is "irqsoff" tracing the time -for which interrupts were disabled. It gives the trace version (which -never changes) and the version of the kernel upon which this was executed on -(3.8). Then it displays the max latency in microseconds (259 us). The number -of trace entries displayed and the total number (both are four: #4/4). -VP, KP, SP, and HP are always zero and are reserved for later use. -#P is the number of online CPUs (#P:4). - -The task is the process that was running when the latency -occurred. (ps pid: 6143). - -The start and stop (the functions in which the interrupts were -disabled and enabled respectively) that caused the latencies: - - __lock_task_sighand is where the interrupts were disabled. - _raw_spin_unlock_irqrestore is where they were enabled again. - -The next lines after the header are the trace itself. The header -explains which is which. - - cmd: The name of the process in the trace. - - pid: The PID of that process. - - CPU#: The CPU which the process was running on. - - irqs-off: 'd' interrupts are disabled. '.' otherwise. - Note: If the architecture does not support a way to - read the irq flags variable, an 'X' will always - be printed here. - - need-resched: - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set, - 'n' only TIF_NEED_RESCHED is set, - 'p' only PREEMPT_NEED_RESCHED is set, - '.' otherwise. - - hardirq/softirq: - 'Z' - NMI occurred inside a hardirq - 'z' - NMI is running - 'H' - hard irq occurred inside a softirq. - 'h' - hard irq is running - 's' - soft irq is running - '.' - normal context. - - preempt-depth: The level of preempt_disabled - -The above is mostly meaningful for kernel developers. - - time: When the latency-format option is enabled, the trace file - output includes a timestamp relative to the start of the - trace. This differs from the output when latency-format - is disabled, which includes an absolute timestamp. - - delay: This is just to help catch your eye a bit better. And - needs to be fixed to be only relative to the same CPU. - The marks are determined by the difference between this - current trace and the next trace. - '$' - greater than 1 second - '@' - greater than 100 milisecond - '*' - greater than 10 milisecond - '#' - greater than 1000 microsecond - '!' - greater than 100 microsecond - '+' - greater than 10 microsecond - ' ' - less than or equal to 10 microsecond. - - The rest is the same as the 'trace' file. - - Note, the latency tracers will usually end with a back trace - to easily find where the latency occurred. - -trace_options -------------- - -The trace_options file (or the options directory) is used to control -what gets printed in the trace output, or manipulate the tracers. -To see what is available, simply cat the file: - - cat trace_options -print-parent -nosym-offset -nosym-addr -noverbose -noraw -nohex -nobin -noblock -trace_printk -annotate -nouserstacktrace -nosym-userobj -noprintk-msg-only -context-info -nolatency-format -record-cmd -norecord-tgid -overwrite -nodisable_on_free -irq-info -markers -noevent-fork -function-trace -nofunction-fork -nodisplay-graph -nostacktrace -nobranch - -To disable one of the options, echo in the option prepended with -"no". - - echo noprint-parent > trace_options - -To enable an option, leave off the "no". - - echo sym-offset > trace_options - -Here are the available options: - - print-parent - On function traces, display the calling (parent) - function as well as the function being traced. - - print-parent: - bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul - - noprint-parent: - bash-4000 [01] 1477.606694: simple_strtoul - - - sym-offset - Display not only the function name, but also the - offset in the function. For example, instead of - seeing just "ktime_get", you will see - "ktime_get+0xb/0x20". - - sym-offset: - bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0 - - sym-addr - this will also display the function address as well - as the function name. - - sym-addr: - bash-4000 [01] 1477.606694: simple_strtoul <c0339346> - - verbose - This deals with the trace file when the - latency-format option is enabled. - - bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \ - (+0.000ms): simple_strtoul (kstrtoul) - - raw - This will display raw numbers. This option is best for - use with user applications that can translate the raw - numbers better than having it done in the kernel. - - hex - Similar to raw, but the numbers will be in a hexadecimal - format. - - bin - This will print out the formats in raw binary. - - block - When set, reading trace_pipe will not block when polled. - - trace_printk - Can disable trace_printk() from writing into the buffer. - - annotate - It is sometimes confusing when the CPU buffers are full - and one CPU buffer had a lot of events recently, thus - a shorter time frame, were another CPU may have only had - a few events, which lets it have older events. When - the trace is reported, it shows the oldest events first, - and it may look like only one CPU ran (the one with the - oldest events). When the annotate option is set, it will - display when a new CPU buffer started: - - <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on - <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on - <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore -##### CPU 2 buffer started #### - <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle - <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog - <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock - - userstacktrace - This option changes the trace. It records a - stacktrace of the current user space thread after - each trace event. - - sym-userobj - when user stacktrace are enabled, look up which - object the address belongs to, and print a - relative address. This is especially useful when - ASLR is on, otherwise you don't get a chance to - resolve the address to object/file/line after - the app is no longer running - - The lookup is performed when you read - trace,trace_pipe. Example: - - a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0 -x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] - - - printk-msg-only - When set, trace_printk()s will only show the format - and not their parameters (if trace_bprintk() or - trace_bputs() was used to save the trace_printk()). - - context-info - Show only the event data. Hides the comm, PID, - timestamp, CPU, and other useful data. - - latency-format - This option changes the trace output. When it is enabled, - the trace displays additional information about the - latency, as described in "Latency trace format". - - record-cmd - When any event or tracer is enabled, a hook is enabled - in the sched_switch trace point to fill comm cache - with mapped pids and comms. But this may cause some - overhead, and if you only care about pids, and not the - name of the task, disabling this option can lower the - impact of tracing. See "saved_cmdlines". - - record-tgid - When any event or tracer is enabled, a hook is enabled - in the sched_switch trace point to fill the cache of - mapped Thread Group IDs (TGID) mapping to pids. See - "saved_tgids". - - overwrite - This controls what happens when the trace buffer is - full. If "1" (default), the oldest events are - discarded and overwritten. If "0", then the newest - events are discarded. - (see per_cpu/cpu0/stats for overrun and dropped) - - disable_on_free - When the free_buffer is closed, tracing will - stop (tracing_on set to 0). - - irq-info - Shows the interrupt, preempt count, need resched data. - When disabled, the trace looks like: - -# tracer: function -# -# entries-in-buffer/entries-written: 144405/9452052 #P:4 -# -# TASK-PID CPU# TIMESTAMP FUNCTION -# | | | | | - <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up - <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89 - <idle>-0 [002] 23636.756055: enqueue_task <-activate_task - - - markers - When set, the trace_marker is writable (only by root). - When disabled, the trace_marker will error with EINVAL - on write. - - event-fork - When set, tasks with PIDs listed in set_event_pid will have - the PIDs of their children added to set_event_pid when those - tasks fork. Also, when tasks with PIDs in set_event_pid exit, - their PIDs will be removed from the file. - - function-trace - The latency tracers will enable function tracing - if this option is enabled (default it is). When - it is disabled, the latency tracers do not trace - functions. This keeps the overhead of the tracer down - when performing latency tests. - - function-fork - When set, tasks with PIDs listed in set_ftrace_pid will - have the PIDs of their children added to set_ftrace_pid - when those tasks fork. Also, when tasks with PIDs in - set_ftrace_pid exit, their PIDs will be removed from the - file. - - display-graph - When set, the latency tracers (irqsoff, wakeup, etc) will - use function graph tracing instead of function tracing. - - stacktrace - When set, a stack trace is recorded after any trace event - is recorded. - - branch - Enable branch tracing with the tracer. This enables branch - tracer along with the currently set tracer. Enabling this - with the "nop" tracer is the same as just enabling the - "branch" tracer. - - Note: Some tracers have their own options. They only appear in this - file when the tracer is active. They always appear in the - options directory. - - -Here are the per tracer options: - -Options for function tracer: - - func_stack_trace - When set, a stack trace is recorded after every - function that is recorded. NOTE! Limit the functions - that are recorded before enabling this, with - "set_ftrace_filter" otherwise the system performance - will be critically degraded. Remember to disable - this option before clearing the function filter. - -Options for function_graph tracer: - - Since the function_graph tracer has a slightly different output - it has its own options to control what is displayed. - - funcgraph-overrun - When set, the "overrun" of the graph stack is - displayed after each function traced. The - overrun, is when the stack depth of the calls - is greater than what is reserved for each task. - Each task has a fixed array of functions to - trace in the call graph. If the depth of the - calls exceeds that, the function is not traced. - The overrun is the number of functions missed - due to exceeding this array. - - funcgraph-cpu - When set, the CPU number of the CPU where the trace - occurred is displayed. - - funcgraph-overhead - When set, if the function takes longer than - A certain amount, then a delay marker is - displayed. See "delay" above, under the - header description. - - funcgraph-proc - Unlike other tracers, the process' command line - is not displayed by default, but instead only - when a task is traced in and out during a context - switch. Enabling this options has the command - of each process displayed at every line. - - funcgraph-duration - At the end of each function (the return) - the duration of the amount of time in the - function is displayed in microseconds. - - funcgraph-abstime - When set, the timestamp is displayed at each - line. - - funcgraph-irqs - When disabled, functions that happen inside an - interrupt will not be traced. - - funcgraph-tail - When set, the return event will include the function - that it represents. By default this is off, and - only a closing curly bracket "}" is displayed for - the return of a function. - - sleep-time - When running function graph tracer, to include - the time a task schedules out in its function. - When enabled, it will account time the task has been - scheduled out as part of the function call. - - graph-time - When running function profiler with function graph tracer, - to include the time to call nested functions. When this is - not set, the time reported for the function will only - include the time the function itself executed for, not the - time for functions that it called. - -Options for blk tracer: - - blk_classic - Shows a more minimalistic output. - - -irqsoff -------- - -When interrupts are disabled, the CPU can not react to any other -external event (besides NMIs and SMIs). This prevents the timer -interrupt from triggering or the mouse interrupt from letting -the kernel know of a new mouse event. The result is a latency -with the reaction time. - -The irqsoff tracer tracks the time for which interrupts are -disabled. When a new maximum latency is hit, the tracer saves -the trace leading up to that latency point so that every time a -new maximum is reached, the old saved trace is discarded and the -new trace is saved. - -To reset the maximum, echo 0 into tracing_max_latency. Here is -an example: - - # echo 0 > options/function-trace - # echo irqsoff > current_tracer - # echo 1 > tracing_on - # echo 0 > tracing_max_latency - # ls -ltr - [...] - # echo 0 > tracing_on - # cat trace -# tracer: irqsoff -# -# irqsoff latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0) -# ----------------- -# => started at: run_timer_softirq -# => ended at: run_timer_softirq -# -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq - <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq - <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq - <idle>-0 0dNs3 25us : <stack trace> - => _raw_spin_unlock_irq - => run_timer_softirq - => __do_softirq - => call_softirq - => do_softirq - => irq_exit - => smp_apic_timer_interrupt - => apic_timer_interrupt - => rcu_idle_exit - => cpu_idle - => rest_init - => start_kernel - => x86_64_start_reservations - => x86_64_start_kernel - -Here we see that that we had a latency of 16 microseconds (which is -very good). The _raw_spin_lock_irq in run_timer_softirq disabled -interrupts. The difference between the 16 and the displayed -timestamp 25us occurred because the clock was incremented -between the time of recording the max latency and the time of -recording the function that had that latency. - -Note the above example had function-trace not set. If we set -function-trace, we get a much larger output: - - with echo 1 > options/function-trace - -# tracer: irqsoff -# -# irqsoff latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0) -# ----------------- -# => started at: ata_scsi_queuecmd -# => ended at: ata_scsi_queuecmd -# -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd - bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave - bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd - bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev - bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev - bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd - bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd - bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd - bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat -[...] - bash-2042 3d..1 67us : delay_tsc <-__delay - bash-2042 3d..1 67us : add_preempt_count <-delay_tsc - bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc - bash-2042 3d..1 67us : add_preempt_count <-delay_tsc - bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc - bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue - bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd - bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd - bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd - bash-2042 3d..1 120us : <stack trace> - => _raw_spin_unlock_irqrestore - => ata_scsi_queuecmd - => scsi_dispatch_cmd - => scsi_request_fn - => __blk_run_queue_uncond - => __blk_run_queue - => blk_queue_bio - => generic_make_request - => submit_bio - => submit_bh - => __ext3_get_inode_loc - => ext3_iget - => ext3_lookup - => lookup_real - => __lookup_hash - => walk_component - => lookup_last - => path_lookupat - => filename_lookup - => user_path_at_empty - => user_path_at - => vfs_fstatat - => vfs_stat - => sys_newstat - => system_call_fastpath - - -Here we traced a 71 microsecond latency. But we also see all the -functions that were called during that time. Note that by -enabling function tracing, we incur an added overhead. This -overhead may extend the latency times. But nevertheless, this -trace has provided some very helpful debugging information. - - -preemptoff ----------- - -When preemption is disabled, we may be able to receive -interrupts but the task cannot be preempted and a higher -priority task must wait for preemption to be enabled again -before it can preempt a lower priority task. - -The preemptoff tracer traces the places that disable preemption. -Like the irqsoff tracer, it records the maximum latency for -which preemption was disabled. The control of preemptoff tracer -is much like the irqsoff tracer. - - # echo 0 > options/function-trace - # echo preemptoff > current_tracer - # echo 1 > tracing_on - # echo 0 > tracing_max_latency - # ls -ltr - [...] - # echo 0 > tracing_on - # cat trace -# tracer: preemptoff -# -# preemptoff latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0) -# ----------------- -# => started at: do_IRQ -# => ended at: do_IRQ -# -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ - sshd-1991 1d..1 46us : irq_exit <-do_IRQ - sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ - sshd-1991 1d..1 52us : <stack trace> - => sub_preempt_count - => irq_exit - => do_IRQ - => ret_from_intr - - -This has some more changes. Preemption was disabled when an -interrupt came in (notice the 'h'), and was enabled on exit. -But we also see that interrupts have been disabled when entering -the preempt off section and leaving it (the 'd'). We do not know if -interrupts were enabled in the mean time or shortly after this -was over. - -# tracer: preemptoff -# -# preemptoff latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0) -# ----------------- -# => started at: wake_up_new_task -# => ended at: task_rq_unlock -# -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task - bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq - bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair - bash-1994 1d..1 1us : source_load <-select_task_rq_fair - bash-1994 1d..1 1us : source_load <-select_task_rq_fair -[...] - bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt - bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter - bash-1994 1d..1 13us : add_preempt_count <-irq_enter - bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt - bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt - bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt - bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock - bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt -[...] - bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event - bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt - bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit - bash-1994 1d..2 36us : do_softirq <-irq_exit - bash-1994 1d..2 36us : __do_softirq <-call_softirq - bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq - bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq - bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq - bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock - bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq -[...] - bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks - bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq - bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable - bash-1994 1dN.2 82us : idle_cpu <-irq_exit - bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit - bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit - bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock - bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock - bash-1994 1.N.1 104us : <stack trace> - => sub_preempt_count - => _raw_spin_unlock_irqrestore - => task_rq_unlock - => wake_up_new_task - => do_fork - => sys_clone - => stub_clone - - -The above is an example of the preemptoff trace with -function-trace set. Here we see that interrupts were not disabled -the entire time. The irq_enter code lets us know that we entered -an interrupt 'h'. Before that, the functions being traced still -show that it is not in an interrupt, but we can see from the -functions themselves that this is not the case. - -preemptirqsoff --------------- - -Knowing the locations that have interrupts disabled or -preemption disabled for the longest times is helpful. But -sometimes we would like to know when either preemption and/or -interrupts are disabled. - -Consider the following code: - - local_irq_disable(); - call_function_with_irqs_off(); - preempt_disable(); - call_function_with_irqs_and_preemption_off(); - local_irq_enable(); - call_function_with_preemption_off(); - preempt_enable(); - -The irqsoff tracer will record the total length of -call_function_with_irqs_off() and -call_function_with_irqs_and_preemption_off(). - -The preemptoff tracer will record the total length of -call_function_with_irqs_and_preemption_off() and -call_function_with_preemption_off(). - -But neither will trace the time that interrupts and/or -preemption is disabled. This total time is the time that we can -not schedule. To record this time, use the preemptirqsoff -tracer. - -Again, using this trace is much like the irqsoff and preemptoff -tracers. - - # echo 0 > options/function-trace - # echo preemptirqsoff > current_tracer - # echo 1 > tracing_on - # echo 0 > tracing_max_latency - # ls -ltr - [...] - # echo 0 > tracing_on - # cat trace -# tracer: preemptirqsoff -# -# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0) -# ----------------- -# => started at: ata_scsi_queuecmd -# => ended at: ata_scsi_queuecmd -# -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd - ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd - ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd - ls-2230 3...1 111us : <stack trace> - => sub_preempt_count - => _raw_spin_unlock_irqrestore - => ata_scsi_queuecmd - => scsi_dispatch_cmd - => scsi_request_fn - => __blk_run_queue_uncond - => __blk_run_queue - => blk_queue_bio - => generic_make_request - => submit_bio - => submit_bh - => ext3_bread - => ext3_dir_bread - => htree_dirblock_to_tree - => ext3_htree_fill_tree - => ext3_readdir - => vfs_readdir - => sys_getdents - => system_call_fastpath - - -The trace_hardirqs_off_thunk is called from assembly on x86 when -interrupts are disabled in the assembly code. Without the -function tracing, we do not know if interrupts were enabled -within the preemption points. We do see that it started with -preemption enabled. - -Here is a trace with function-trace set: - -# tracer: preemptirqsoff -# -# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0) -# ----------------- -# => started at: schedule -# => ended at: mutex_unlock -# -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / -kworker/-59 3...1 0us : __schedule <-schedule -kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch -kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq -kworker/-59 3d..2 1us : deactivate_task <-__schedule -kworker/-59 3d..2 1us : dequeue_task <-deactivate_task -kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task -kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task -kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair -kworker/-59 3d..2 2us : update_min_vruntime <-update_curr -kworker/-59 3d..2 3us : cpuacct_charge <-update_curr -kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge -kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge -kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair -kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair -kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair -kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair -kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair -kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair -kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule -kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping -kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule -kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task -kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair -kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair -kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity - ls-2269 3d..2 7us : finish_task_switch <-__schedule - ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch - ls-2269 3d..2 8us : do_IRQ <-ret_from_intr - ls-2269 3d..2 8us : irq_enter <-do_IRQ - ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter - ls-2269 3d..2 9us : add_preempt_count <-irq_enter - ls-2269 3d.h2 9us : exit_idle <-do_IRQ -[...] - ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock - ls-2269 3d.h2 20us : irq_exit <-do_IRQ - ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit - ls-2269 3d..3 21us : do_softirq <-irq_exit - ls-2269 3d..3 21us : __do_softirq <-call_softirq - ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq - ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip - ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip - ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr - ls-2269 3d.s5 31us : irq_enter <-do_IRQ - ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter -[...] - ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter - ls-2269 3d.s5 32us : add_preempt_count <-irq_enter - ls-2269 3d.H5 32us : exit_idle <-do_IRQ - ls-2269 3d.H5 32us : handle_irq <-do_IRQ - ls-2269 3d.H5 32us : irq_to_desc <-handle_irq - ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq -[...] - ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll - ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action - ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq - ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable - ls-2269 3d..3 159us : idle_cpu <-irq_exit - ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit - ls-2269 3d..3 160us : sub_preempt_count <-irq_exit - ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock - ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock - ls-2269 3d... 186us : <stack trace> - => __mutex_unlock_slowpath - => mutex_unlock - => process_output - => n_tty_write - => tty_write - => vfs_write - => sys_write - => system_call_fastpath - -This is an interesting trace. It started with kworker running and -scheduling out and ls taking over. But as soon as ls released the -rq lock and enabled interrupts (but not preemption) an interrupt -triggered. When the interrupt finished, it started running softirqs. -But while the softirq was running, another interrupt triggered. -When an interrupt is running inside a softirq, the annotation is 'H'. - - -wakeup ------- - -One common case that people are interested in tracing is the -time it takes for a task that is woken to actually wake up. -Now for non Real-Time tasks, this can be arbitrary. But tracing -it none the less can be interesting. - -Without function tracing: - - # echo 0 > options/function-trace - # echo wakeup > current_tracer - # echo 1 > tracing_on - # echo 0 > tracing_max_latency - # chrt -f 5 sleep 1 - # echo 0 > tracing_on - # cat trace -# tracer: wakeup -# -# wakeup latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0) -# ----------------- -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H - <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up - <idle>-0 3d..3 15us : __schedule <-schedule - <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H - -The tracer only traces the highest priority task in the system -to avoid tracing the normal circumstances. Here we see that -the kworker with a nice priority of -20 (not very nice), took -just 15 microseconds from the time it woke up, to the time it -ran. - -Non Real-Time tasks are not that interesting. A more interesting -trace is to concentrate only on Real-Time tasks. - -wakeup_rt ---------- - -In a Real-Time environment it is very important to know the -wakeup time it takes for the highest priority task that is woken -up to the time that it executes. This is also known as "schedule -latency". I stress the point that this is about RT tasks. It is -also important to know the scheduling latency of non-RT tasks, -but the average schedule latency is better for non-RT tasks. -Tools like LatencyTop are more appropriate for such -measurements. - -Real-Time environments are interested in the worst case latency. -That is the longest latency it takes for something to happen, -and not the average. We can have a very fast scheduler that may -only have a large latency once in a while, but that would not -work well with Real-Time tasks. The wakeup_rt tracer was designed -to record the worst case wakeups of RT tasks. Non-RT tasks are -not recorded because the tracer only records one worst case and -tracing non-RT tasks that are unpredictable will overwrite the -worst case latency of RT tasks (just run the normal wakeup -tracer for a while to see that effect). - -Since this tracer only deals with RT tasks, we will run this -slightly differently than we did with the previous tracers. -Instead of performing an 'ls', we will run 'sleep 1' under -'chrt' which changes the priority of the task. - - # echo 0 > options/function-trace - # echo wakeup_rt > current_tracer - # echo 1 > tracing_on - # echo 0 > tracing_max_latency - # chrt -f 5 sleep 1 - # echo 0 > tracing_on - # cat trace -# tracer: wakeup -# -# tracer: wakeup_rt -# -# wakeup_rt latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5) -# ----------------- -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep - <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up - <idle>-0 3d..3 5us : __schedule <-schedule - <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep - - -Running this on an idle system, we see that it only took 5 microseconds -to perform the task switch. Note, since the trace point in the schedule -is before the actual "switch", we stop the tracing when the recorded task -is about to schedule in. This may change if we add a new marker at the -end of the scheduler. - -Notice that the recorded task is 'sleep' with the PID of 2389 -and it has an rt_prio of 5. This priority is user-space priority -and not the internal kernel priority. The policy is 1 for -SCHED_FIFO and 2 for SCHED_RR. - -Note, that the trace data shows the internal priority (99 - rtprio). - - <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep - -The 0:120:R means idle was running with a nice priority of 0 (120 - 120) -and in the running state 'R'. The sleep task was scheduled in with -2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94) -and it too is in the running state. - -Doing the same with chrt -r 5 and function-trace set. - - echo 1 > options/function-trace - -# tracer: wakeup_rt -# -# wakeup_rt latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5) -# ----------------- -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep - <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up - <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup - <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr - <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup - <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up - <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock - <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up - <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up - <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore - <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer - <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock - <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt - <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock - <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt - <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event - <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event - <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event - <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt - <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit - <idle>-0 3dN.2 9us : idle_cpu <-irq_exit - <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit - <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit - <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit - <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle - <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit - <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle - <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit - <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit - <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit - <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit - <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz - <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock - <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz - <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update - <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz - <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock - <idle>-0 3dN.1 15us : calc_load_nohz_stop <-tick_nohz_idle_exit - <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit - <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit - <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel - <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel - <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 - <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave - <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16 - <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer - <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram - <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event - <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event - <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event - <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel - <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore - <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit - <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward - <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward - <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 - <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns - <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns - <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 - <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave - <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns - <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns - <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns - <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event - <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event - <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event - <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns - <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore - <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit - <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks - <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle - <idle>-0 3.N.. 25us : schedule <-cpu_idle - <idle>-0 3.N.. 25us : __schedule <-preempt_schedule - <idle>-0 3.N.. 26us : add_preempt_count <-__schedule - <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule - <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch - <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch - <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule - <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq - <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule - <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task - <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task - <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt - <idle>-0 3d..3 29us : __schedule <-preempt_schedule - <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep - -This isn't that big of a trace, even with function tracing enabled, -so I included the entire trace. - -The interrupt went off while when the system was idle. Somewhere -before task_woken_rt() was called, the NEED_RESCHED flag was set, -this is indicated by the first occurrence of the 'N' flag. - -Latency tracing and events --------------------------- -As function tracing can induce a much larger latency, but without -seeing what happens within the latency it is hard to know what -caused it. There is a middle ground, and that is with enabling -events. - - # echo 0 > options/function-trace - # echo wakeup_rt > current_tracer - # echo 1 > events/enable - # echo 1 > tracing_on - # echo 0 > tracing_max_latency - # chrt -f 5 sleep 1 - # echo 0 > tracing_on - # cat trace -# tracer: wakeup_rt -# -# wakeup_rt latency trace v1.1.5 on 3.8.0-test+ -# -------------------------------------------------------------------- -# latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) -# ----------------- -# | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5) -# ----------------- -# -# _------=> CPU# -# / _-----=> irqs-off -# | / _----=> need-resched -# || / _---=> hardirq/softirq -# ||| / _--=> preempt-depth -# |||| / delay -# cmd pid ||||| time | caller -# \ / ||||| \ | / - <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep - <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up - <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002 - <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8 - <idle>-0 2.N.2 2us : power_end: cpu_id=2 - <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2 - <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0 - <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000 - <idle>-0 2.N.2 5us : rcu_utilization: Start context switch - <idle>-0 2.N.2 5us : rcu_utilization: End context switch - <idle>-0 2d..3 6us : __schedule <-schedule - <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep - - -Hardware Latency Detector -------------------------- - -The hardware latency detector is executed by enabling the "hwlat" tracer. - -NOTE, this tracer will affect the performance of the system as it will -periodically make a CPU constantly busy with interrupts disabled. - - # echo hwlat > current_tracer - # sleep 100 - # cat trace -# tracer: hwlat -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - <...>-3638 [001] d... 19452.055471: #1 inner/outer(us): 12/14 ts:1499801089.066141940 - <...>-3638 [003] d... 19454.071354: #2 inner/outer(us): 11/9 ts:1499801091.082164365 - <...>-3638 [002] dn.. 19461.126852: #3 inner/outer(us): 12/9 ts:1499801098.138150062 - <...>-3638 [001] d... 19488.340960: #4 inner/outer(us): 8/12 ts:1499801125.354139633 - <...>-3638 [003] d... 19494.388553: #5 inner/outer(us): 8/12 ts:1499801131.402150961 - <...>-3638 [003] d... 19501.283419: #6 inner/outer(us): 0/12 ts:1499801138.297435289 nmi-total:4 nmi-count:1 - - -The above output is somewhat the same in the header. All events will have -interrupts disabled 'd'. Under the FUNCTION title there is: - - #1 - This is the count of events recorded that were greater than the - tracing_threshold (See below). - - inner/outer(us): 12/14 - - This shows two numbers as "inner latency" and "outer latency". The test - runs in a loop checking a timestamp twice. The latency detected within - the two timestamps is the "inner latency" and the latency detected - after the previous timestamp and the next timestamp in the loop is - the "outer latency". - - ts:1499801089.066141940 - - The absolute timestamp that the event happened. - - nmi-total:4 nmi-count:1 - - On architectures that support it, if an NMI comes in during the - test, the time spent in NMI is reported in "nmi-total" (in - microseconds). - - All architectures that have NMIs will show the "nmi-count" if an - NMI comes in during the test. - -hwlat files: - - tracing_threshold - This gets automatically set to "10" to represent 10 - microseconds. This is the threshold of latency that - needs to be detected before the trace will be recorded. - - Note, when hwlat tracer is finished (another tracer is - written into "current_tracer"), the original value for - tracing_threshold is placed back into this file. - - hwlat_detector/width - The length of time the test runs with interrupts - disabled. - - hwlat_detector/window - The length of time of the window which the test - runs. That is, the test will run for "width" - microseconds per "window" microseconds - - tracing_cpumask - When the test is started. A kernel thread is created that - runs the test. This thread will alternate between CPUs - listed in the tracing_cpumask between each period - (one "window"). To limit the test to specific CPUs - set the mask in this file to only the CPUs that the test - should run on. - -function --------- - -This tracer is the function tracer. Enabling the function tracer -can be done from the debug file system. Make sure the -ftrace_enabled is set; otherwise this tracer is a nop. -See the "ftrace_enabled" section below. - - # sysctl kernel.ftrace_enabled=1 - # echo function > current_tracer - # echo 1 > tracing_on - # usleep 1 - # echo 0 > tracing_on - # cat trace -# tracer: function -# -# entries-in-buffer/entries-written: 24799/24799 #P:4 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write - bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock - bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify - bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify - bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify - bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock - bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock - bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify -[...] - - -Note: function tracer uses ring buffers to store the above -entries. The newest data may overwrite the oldest data. -Sometimes using echo to stop the trace is not sufficient because -the tracing could have overwritten the data that you wanted to -record. For this reason, it is sometimes better to disable -tracing directly from a program. This allows you to stop the -tracing at the point that you hit the part that you are -interested in. To disable the tracing directly from a C program, -something like following code snippet can be used: - -int trace_fd; -[...] -int main(int argc, char *argv[]) { - [...] - trace_fd = open(tracing_file("tracing_on"), O_WRONLY); - [...] - if (condition_hit()) { - write(trace_fd, "0", 1); - } - [...] -} - - -Single thread tracing ---------------------- - -By writing into set_ftrace_pid you can trace a -single thread. For example: - -# cat set_ftrace_pid -no pid -# echo 3111 > set_ftrace_pid -# cat set_ftrace_pid -3111 -# echo function > current_tracer -# cat trace | head - # tracer: function - # - # TASK-PID CPU# TIMESTAMP FUNCTION - # | | | | | - yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return - yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range - yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel - yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel - yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll - yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll -# echo > set_ftrace_pid -# cat trace |head - # tracer: function - # - # TASK-PID CPU# TIMESTAMP FUNCTION - # | | | | | - ##### CPU 3 buffer started #### - yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait - yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry - yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry - yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit - yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit - -If you want to trace a function when executing, you could use -something like this simple program: - -#include <stdio.h> -#include <stdlib.h> -#include <sys/types.h> -#include <sys/stat.h> -#include <fcntl.h> -#include <unistd.h> -#include <string.h> - -#define _STR(x) #x -#define STR(x) _STR(x) -#define MAX_PATH 256 - -const char *find_tracefs(void) -{ - static char tracefs[MAX_PATH+1]; - static int tracefs_found; - char type[100]; - FILE *fp; - - if (tracefs_found) - return tracefs; - - if ((fp = fopen("/proc/mounts","r")) == NULL) { - perror("/proc/mounts"); - return NULL; - } - - while (fscanf(fp, "%*s %" - STR(MAX_PATH) - "s %99s %*s %*d %*d\n", - tracefs, type) == 2) { - if (strcmp(type, "tracefs") == 0) - break; - } - fclose(fp); - - if (strcmp(type, "tracefs") != 0) { - fprintf(stderr, "tracefs not mounted"); - return NULL; - } - - strcat(tracefs, "/tracing/"); - tracefs_found = 1; - - return tracefs; -} - -const char *tracing_file(const char *file_name) -{ - static char trace_file[MAX_PATH+1]; - snprintf(trace_file, MAX_PATH, "%s/%s", find_tracefs(), file_name); - return trace_file; -} - -int main (int argc, char **argv) -{ - if (argc < 1) - exit(-1); - - if (fork() > 0) { - int fd, ffd; - char line[64]; - int s; - - ffd = open(tracing_file("current_tracer"), O_WRONLY); - if (ffd < 0) - exit(-1); - write(ffd, "nop", 3); - - fd = open(tracing_file("set_ftrace_pid"), O_WRONLY); - s = sprintf(line, "%d\n", getpid()); - write(fd, line, s); - - write(ffd, "function", 8); - - close(fd); - close(ffd); - - execvp(argv[1], argv+1); - } - - return 0; -} - -Or this simple script! - ------- -#!/bin/bash - -tracefs=`sed -ne 's/^tracefs \(.*\) tracefs.*/\1/p' /proc/mounts` -echo nop > $tracefs/tracing/current_tracer -echo 0 > $tracefs/tracing/tracing_on -echo $$ > $tracefs/tracing/set_ftrace_pid -echo function > $tracefs/tracing/current_tracer -echo 1 > $tracefs/tracing/tracing_on -exec "$@" ------- - - -function graph tracer ---------------------------- - -This tracer is similar to the function tracer except that it -probes a function on its entry and its exit. This is done by -using a dynamically allocated stack of return addresses in each -task_struct. On function entry the tracer overwrites the return -address of each function traced to set a custom probe. Thus the -original return address is stored on the stack of return address -in the task_struct. - -Probing on both ends of a function leads to special features -such as: - -- measure of a function's time execution -- having a reliable call stack to draw function calls graph - -This tracer is useful in several situations: - -- you want to find the reason of a strange kernel behavior and - need to see what happens in detail on any areas (or specific - ones). - -- you are experiencing weird latencies but it's difficult to - find its origin. - -- you want to find quickly which path is taken by a specific - function - -- you just want to peek inside a working kernel and want to see - what happens there. - -# tracer: function_graph -# -# CPU DURATION FUNCTION CALLS -# | | | | | | | - - 0) | sys_open() { - 0) | do_sys_open() { - 0) | getname() { - 0) | kmem_cache_alloc() { - 0) 1.382 us | __might_sleep(); - 0) 2.478 us | } - 0) | strncpy_from_user() { - 0) | might_fault() { - 0) 1.389 us | __might_sleep(); - 0) 2.553 us | } - 0) 3.807 us | } - 0) 7.876 us | } - 0) | alloc_fd() { - 0) 0.668 us | _spin_lock(); - 0) 0.570 us | expand_files(); - 0) 0.586 us | _spin_unlock(); - - -There are several columns that can be dynamically -enabled/disabled. You can use every combination of options you -want, depending on your needs. - -- The cpu number on which the function executed is default - enabled. It is sometimes better to only trace one cpu (see - tracing_cpu_mask file) or you might sometimes see unordered - function calls while cpu tracing switch. - - hide: echo nofuncgraph-cpu > trace_options - show: echo funcgraph-cpu > trace_options - -- The duration (function's time of execution) is displayed on - the closing bracket line of a function or on the same line - than the current function in case of a leaf one. It is default - enabled. - - hide: echo nofuncgraph-duration > trace_options - show: echo funcgraph-duration > trace_options - -- The overhead field precedes the duration field in case of - reached duration thresholds. - - hide: echo nofuncgraph-overhead > trace_options - show: echo funcgraph-overhead > trace_options - depends on: funcgraph-duration - - ie: - - 3) # 1837.709 us | } /* __switch_to */ - 3) | finish_task_switch() { - 3) 0.313 us | _raw_spin_unlock_irq(); - 3) 3.177 us | } - 3) # 1889.063 us | } /* __schedule */ - 3) ! 140.417 us | } /* __schedule */ - 3) # 2034.948 us | } /* schedule */ - 3) * 33998.59 us | } /* schedule_preempt_disabled */ - - [...] - - 1) 0.260 us | msecs_to_jiffies(); - 1) 0.313 us | __rcu_read_unlock(); - 1) + 61.770 us | } - 1) + 64.479 us | } - 1) 0.313 us | rcu_bh_qs(); - 1) 0.313 us | __local_bh_enable(); - 1) ! 217.240 us | } - 1) 0.365 us | idle_cpu(); - 1) | rcu_irq_exit() { - 1) 0.417 us | rcu_eqs_enter_common.isra.47(); - 1) 3.125 us | } - 1) ! 227.812 us | } - 1) ! 457.395 us | } - 1) @ 119760.2 us | } - - [...] - - 2) | handle_IPI() { - 1) 6.979 us | } - 2) 0.417 us | scheduler_ipi(); - 1) 9.791 us | } - 1) + 12.917 us | } - 2) 3.490 us | } - 1) + 15.729 us | } - 1) + 18.542 us | } - 2) $ 3594274 us | } - - + means that the function exceeded 10 usecs. - ! means that the function exceeded 100 usecs. - # means that the function exceeded 1000 usecs. - * means that the function exceeded 10 msecs. - @ means that the function exceeded 100 msecs. - $ means that the function exceeded 1 sec. - - -- The task/pid field displays the thread cmdline and pid which - executed the function. It is default disabled. - - hide: echo nofuncgraph-proc > trace_options - show: echo funcgraph-proc > trace_options - - ie: - - # tracer: function_graph - # - # CPU TASK/PID DURATION FUNCTION CALLS - # | | | | | | | | | - 0) sh-4802 | | d_free() { - 0) sh-4802 | | call_rcu() { - 0) sh-4802 | | __call_rcu() { - 0) sh-4802 | 0.616 us | rcu_process_gp_end(); - 0) sh-4802 | 0.586 us | check_for_new_grace_period(); - 0) sh-4802 | 2.899 us | } - 0) sh-4802 | 4.040 us | } - 0) sh-4802 | 5.151 us | } - 0) sh-4802 | + 49.370 us | } - - -- The absolute time field is an absolute timestamp given by the - system clock since it started. A snapshot of this time is - given on each entry/exit of functions - - hide: echo nofuncgraph-abstime > trace_options - show: echo funcgraph-abstime > trace_options - - ie: - - # - # TIME CPU DURATION FUNCTION CALLS - # | | | | | | | | - 360.774522 | 1) 0.541 us | } - 360.774522 | 1) 4.663 us | } - 360.774523 | 1) 0.541 us | __wake_up_bit(); - 360.774524 | 1) 6.796 us | } - 360.774524 | 1) 7.952 us | } - 360.774525 | 1) 9.063 us | } - 360.774525 | 1) 0.615 us | journal_mark_dirty(); - 360.774527 | 1) 0.578 us | __brelse(); - 360.774528 | 1) | reiserfs_prepare_for_journal() { - 360.774528 | 1) | unlock_buffer() { - 360.774529 | 1) | wake_up_bit() { - 360.774529 | 1) | bit_waitqueue() { - 360.774530 | 1) 0.594 us | __phys_addr(); - - -The function name is always displayed after the closing bracket -for a function if the start of that function is not in the -trace buffer. - -Display of the function name after the closing bracket may be -enabled for functions whose start is in the trace buffer, -allowing easier searching with grep for function durations. -It is default disabled. - - hide: echo nofuncgraph-tail > trace_options - show: echo funcgraph-tail > trace_options - - Example with nofuncgraph-tail (default): - 0) | putname() { - 0) | kmem_cache_free() { - 0) 0.518 us | __phys_addr(); - 0) 1.757 us | } - 0) 2.861 us | } - - Example with funcgraph-tail: - 0) | putname() { - 0) | kmem_cache_free() { - 0) 0.518 us | __phys_addr(); - 0) 1.757 us | } /* kmem_cache_free() */ - 0) 2.861 us | } /* putname() */ - -You can put some comments on specific functions by using -trace_printk() For example, if you want to put a comment inside -the __might_sleep() function, you just have to include -<linux/ftrace.h> and call trace_printk() inside __might_sleep() - -trace_printk("I'm a comment!\n") - -will produce: - - 1) | __might_sleep() { - 1) | /* I'm a comment! */ - 1) 1.449 us | } - - -You might find other useful features for this tracer in the -following "dynamic ftrace" section such as tracing only specific -functions or tasks. - -dynamic ftrace --------------- - -If CONFIG_DYNAMIC_FTRACE is set, the system will run with -virtually no overhead when function tracing is disabled. The way -this works is the mcount function call (placed at the start of -every kernel function, produced by the -pg switch in gcc), -starts of pointing to a simple return. (Enabling FTRACE will -include the -pg switch in the compiling of the kernel.) - -At compile time every C file object is run through the -recordmcount program (located in the scripts directory). This -program will parse the ELF headers in the C object to find all -the locations in the .text section that call mcount. Starting -with gcc verson 4.6, the -mfentry has been added for x86, which -calls "__fentry__" instead of "mcount". Which is called before -the creation of the stack frame. - -Note, not all sections are traced. They may be prevented by either -a notrace, or blocked another way and all inline functions are not -traced. Check the "available_filter_functions" file to see what functions -can be traced. - -A section called "__mcount_loc" is created that holds -references to all the mcount/fentry call sites in the .text section. -The recordmcount program re-links this section back into the -original object. The final linking stage of the kernel will add all these -references into a single table. - -On boot up, before SMP is initialized, the dynamic ftrace code -scans this table and updates all the locations into nops. It -also records the locations, which are added to the -available_filter_functions list. Modules are processed as they -are loaded and before they are executed. When a module is -unloaded, it also removes its functions from the ftrace function -list. This is automatic in the module unload code, and the -module author does not need to worry about it. - -When tracing is enabled, the process of modifying the function -tracepoints is dependent on architecture. The old method is to use -kstop_machine to prevent races with the CPUs executing code being -modified (which can cause the CPU to do undesirable things, especially -if the modified code crosses cache (or page) boundaries), and the nops are -patched back to calls. But this time, they do not call mcount -(which is just a function stub). They now call into the ftrace -infrastructure. - -The new method of modifying the function tracepoints is to place -a breakpoint at the location to be modified, sync all CPUs, modify -the rest of the instruction not covered by the breakpoint. Sync -all CPUs again, and then remove the breakpoint with the finished -version to the ftrace call site. - -Some archs do not even need to monkey around with the synchronization, -and can just slap the new code on top of the old without any -problems with other CPUs executing it at the same time. - -One special side-effect to the recording of the functions being -traced is that we can now selectively choose which functions we -wish to trace and which ones we want the mcount calls to remain -as nops. - -Two files are used, one for enabling and one for disabling the -tracing of specified functions. They are: - - set_ftrace_filter - -and - - set_ftrace_notrace - -A list of available functions that you can add to these files is -listed in: - - available_filter_functions - - # cat available_filter_functions -put_prev_task_idle -kmem_cache_create -pick_next_task_rt -get_online_cpus -pick_next_task_fair -mutex_lock -[...] - -If I am only interested in sys_nanosleep and hrtimer_interrupt: - - # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter - # echo function > current_tracer - # echo 1 > tracing_on - # usleep 1 - # echo 0 > tracing_on - # cat trace -# tracer: function -# -# entries-in-buffer/entries-written: 5/5 #P:4 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath - <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt - usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt - <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt - <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt - -To see which functions are being traced, you can cat the file: - - # cat set_ftrace_filter -hrtimer_interrupt -sys_nanosleep - - -Perhaps this is not enough. The filters also allow glob(7) matching. - - <match>* - will match functions that begin with <match> - *<match> - will match functions that end with <match> - *<match>* - will match functions that have <match> in it - <match1>*<match2> - will match functions that begin with - <match1> and end with <match2> - -Note: It is better to use quotes to enclose the wild cards, - otherwise the shell may expand the parameters into names - of files in the local directory. - - # echo 'hrtimer_*' > set_ftrace_filter - -Produces: - -# tracer: function -# -# entries-in-buffer/entries-written: 897/897 #P:4 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit - <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel - <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer - <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit - <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 - <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt - <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter - <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem - -Notice that we lost the sys_nanosleep. - - # cat set_ftrace_filter -hrtimer_run_queues -hrtimer_run_pending -hrtimer_init -hrtimer_cancel -hrtimer_try_to_cancel -hrtimer_forward -hrtimer_start -hrtimer_reprogram -hrtimer_force_reprogram -hrtimer_get_next_event -hrtimer_interrupt -hrtimer_nanosleep -hrtimer_wakeup -hrtimer_get_remaining -hrtimer_get_res -hrtimer_init_sleeper - - -This is because the '>' and '>>' act just like they do in bash. -To rewrite the filters, use '>' -To append to the filters, use '>>' - -To clear out a filter so that all functions will be recorded -again: - - # echo > set_ftrace_filter - # cat set_ftrace_filter - # - -Again, now we want to append. - - # echo sys_nanosleep > set_ftrace_filter - # cat set_ftrace_filter -sys_nanosleep - # echo 'hrtimer_*' >> set_ftrace_filter - # cat set_ftrace_filter -hrtimer_run_queues -hrtimer_run_pending -hrtimer_init -hrtimer_cancel -hrtimer_try_to_cancel -hrtimer_forward -hrtimer_start -hrtimer_reprogram -hrtimer_force_reprogram -hrtimer_get_next_event -hrtimer_interrupt -sys_nanosleep -hrtimer_nanosleep -hrtimer_wakeup -hrtimer_get_remaining -hrtimer_get_res -hrtimer_init_sleeper - - -The set_ftrace_notrace prevents those functions from being -traced. - - # echo '*preempt*' '*lock*' > set_ftrace_notrace - -Produces: - -# tracer: function -# -# entries-in-buffer/entries-written: 39608/39608 #P:4 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open - bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last - bash-1994 [000] .... 4342.324897: ima_file_check <-do_last - bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check - bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement - bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action - bash-1994 [000] .... 4342.324899: do_truncate <-do_last - bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate - bash-1994 [000] .... 4342.324899: notify_change <-do_truncate - bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change - bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time - bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time - -We can see that there's no more lock or preempt tracing. - - -Dynamic ftrace with the function graph tracer ---------------------------------------------- - -Although what has been explained above concerns both the -function tracer and the function-graph-tracer, there are some -special features only available in the function-graph tracer. - -If you want to trace only one function and all of its children, -you just have to echo its name into set_graph_function: - - echo __do_fault > set_graph_function - -will produce the following "expanded" trace of the __do_fault() -function: - - 0) | __do_fault() { - 0) | filemap_fault() { - 0) | find_lock_page() { - 0) 0.804 us | find_get_page(); - 0) | __might_sleep() { - 0) 1.329 us | } - 0) 3.904 us | } - 0) 4.979 us | } - 0) 0.653 us | _spin_lock(); - 0) 0.578 us | page_add_file_rmap(); - 0) 0.525 us | native_set_pte_at(); - 0) 0.585 us | _spin_unlock(); - 0) | unlock_page() { - 0) 0.541 us | page_waitqueue(); - 0) 0.639 us | __wake_up_bit(); - 0) 2.786 us | } - 0) + 14.237 us | } - 0) | __do_fault() { - 0) | filemap_fault() { - 0) | find_lock_page() { - 0) 0.698 us | find_get_page(); - 0) | __might_sleep() { - 0) 1.412 us | } - 0) 3.950 us | } - 0) 5.098 us | } - 0) 0.631 us | _spin_lock(); - 0) 0.571 us | page_add_file_rmap(); - 0) 0.526 us | native_set_pte_at(); - 0) 0.586 us | _spin_unlock(); - 0) | unlock_page() { - 0) 0.533 us | page_waitqueue(); - 0) 0.638 us | __wake_up_bit(); - 0) 2.793 us | } - 0) + 14.012 us | } - -You can also expand several functions at once: - - echo sys_open > set_graph_function - echo sys_close >> set_graph_function - -Now if you want to go back to trace all functions you can clear -this special filter via: - - echo > set_graph_function - - -ftrace_enabled --------------- - -Note, the proc sysctl ftrace_enable is a big on/off switch for the -function tracer. By default it is enabled (when function tracing is -enabled in the kernel). If it is disabled, all function tracing is -disabled. This includes not only the function tracers for ftrace, but -also for any other uses (perf, kprobes, stack tracing, profiling, etc). - -Please disable this with care. - -This can be disable (and enabled) with: - - sysctl kernel.ftrace_enabled=0 - sysctl kernel.ftrace_enabled=1 - - or - - echo 0 > /proc/sys/kernel/ftrace_enabled - echo 1 > /proc/sys/kernel/ftrace_enabled - - -Filter commands ---------------- - -A few commands are supported by the set_ftrace_filter interface. -Trace commands have the following format: - -<function>:<command>:<parameter> - -The following commands are supported: - -- mod - This command enables function filtering per module. The - parameter defines the module. For example, if only the write* - functions in the ext3 module are desired, run: - - echo 'write*:mod:ext3' > set_ftrace_filter - - This command interacts with the filter in the same way as - filtering based on function names. Thus, adding more functions - in a different module is accomplished by appending (>>) to the - filter file. Remove specific module functions by prepending - '!': - - echo '!writeback*:mod:ext3' >> set_ftrace_filter - - Mod command supports module globbing. Disable tracing for all - functions except a specific module: - - echo '!*:mod:!ext3' >> set_ftrace_filter - - Disable tracing for all modules, but still trace kernel: - - echo '!*:mod:*' >> set_ftrace_filter - - Enable filter only for kernel: - - echo '*write*:mod:!*' >> set_ftrace_filter - - Enable filter for module globbing: - - echo '*write*:mod:*snd*' >> set_ftrace_filter - -- traceon/traceoff - These commands turn tracing on and off when the specified - functions are hit. The parameter determines how many times the - tracing system is turned on and off. If unspecified, there is - no limit. For example, to disable tracing when a schedule bug - is hit the first 5 times, run: - - echo '__schedule_bug:traceoff:5' > set_ftrace_filter - - To always disable tracing when __schedule_bug is hit: - - echo '__schedule_bug:traceoff' > set_ftrace_filter - - These commands are cumulative whether or not they are appended - to set_ftrace_filter. To remove a command, prepend it by '!' - and drop the parameter: - - echo '!__schedule_bug:traceoff:0' > set_ftrace_filter - - The above removes the traceoff command for __schedule_bug - that have a counter. To remove commands without counters: - - echo '!__schedule_bug:traceoff' > set_ftrace_filter - -- snapshot - Will cause a snapshot to be triggered when the function is hit. - - echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter - - To only snapshot once: - - echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter - - To remove the above commands: - - echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter - echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter - -- enable_event/disable_event - These commands can enable or disable a trace event. Note, because - function tracing callbacks are very sensitive, when these commands - are registered, the trace point is activated, but disabled in - a "soft" mode. That is, the tracepoint will be called, but - just will not be traced. The event tracepoint stays in this mode - as long as there's a command that triggers it. - - echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \ - set_ftrace_filter - - The format is: - - <function>:enable_event:<system>:<event>[:count] - <function>:disable_event:<system>:<event>[:count] - - To remove the events commands: - - - echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \ - set_ftrace_filter - echo '!schedule:disable_event:sched:sched_switch' > \ - set_ftrace_filter - -- dump - When the function is hit, it will dump the contents of the ftrace - ring buffer to the console. This is useful if you need to debug - something, and want to dump the trace when a certain function - is hit. Perhaps its a function that is called before a tripple - fault happens and does not allow you to get a regular dump. - -- cpudump - When the function is hit, it will dump the contents of the ftrace - ring buffer for the current CPU to the console. Unlike the "dump" - command, it only prints out the contents of the ring buffer for the - CPU that executed the function that triggered the dump. - -trace_pipe ----------- - -The trace_pipe outputs the same content as the trace file, but -the effect on the tracing is different. Every read from -trace_pipe is consumed. This means that subsequent reads will be -different. The trace is live. - - # echo function > current_tracer - # cat trace_pipe > /tmp/trace.out & -[1] 4153 - # echo 1 > tracing_on - # usleep 1 - # echo 0 > tracing_on - # cat trace -# tracer: function -# -# entries-in-buffer/entries-written: 0/0 #P:4 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - - # - # cat /tmp/trace.out - bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write - bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock - bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify - bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify - bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify - bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock - bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock - bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify - bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath - - -Note, reading the trace_pipe file will block until more input is -added. - -trace entries -------------- - -Having too much or not enough data can be troublesome in -diagnosing an issue in the kernel. The file buffer_size_kb is -used to modify the size of the internal trace buffers. The -number listed is the number of entries that can be recorded per -CPU. To know the full size, multiply the number of possible CPUs -with the number of entries. - - # cat buffer_size_kb -1408 (units kilobytes) - -Or simply read buffer_total_size_kb - - # cat buffer_total_size_kb -5632 - -To modify the buffer, simple echo in a number (in 1024 byte segments). - - # echo 10000 > buffer_size_kb - # cat buffer_size_kb -10000 (units kilobytes) - -It will try to allocate as much as possible. If you allocate too -much, it can cause Out-Of-Memory to trigger. - - # echo 1000000000000 > buffer_size_kb --bash: echo: write error: Cannot allocate memory - # cat buffer_size_kb -85 - -The per_cpu buffers can be changed individually as well: - - # echo 10000 > per_cpu/cpu0/buffer_size_kb - # echo 100 > per_cpu/cpu1/buffer_size_kb - -When the per_cpu buffers are not the same, the buffer_size_kb -at the top level will just show an X - - # cat buffer_size_kb -X - -This is where the buffer_total_size_kb is useful: - - # cat buffer_total_size_kb -12916 - -Writing to the top level buffer_size_kb will reset all the buffers -to be the same again. - -Snapshot --------- -CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature -available to all non latency tracers. (Latency tracers which -record max latency, such as "irqsoff" or "wakeup", can't use -this feature, since those are already using the snapshot -mechanism internally.) - -Snapshot preserves a current trace buffer at a particular point -in time without stopping tracing. Ftrace swaps the current -buffer with a spare buffer, and tracing continues in the new -current (=previous spare) buffer. - -The following tracefs files in "tracing" are related to this -feature: - - snapshot: - - This is used to take a snapshot and to read the output - of the snapshot. Echo 1 into this file to allocate a - spare buffer and to take a snapshot (swap), then read - the snapshot from this file in the same format as - "trace" (described above in the section "The File - System"). Both reads snapshot and tracing are executable - in parallel. When the spare buffer is allocated, echoing - 0 frees it, and echoing else (positive) values clear the - snapshot contents. - More details are shown in the table below. - - status\input | 0 | 1 | else | - --------------+------------+------------+------------+ - not allocated |(do nothing)| alloc+swap |(do nothing)| - --------------+------------+------------+------------+ - allocated | free | swap | clear | - --------------+------------+------------+------------+ - -Here is an example of using the snapshot feature. - - # echo 1 > events/sched/enable - # echo 1 > snapshot - # cat snapshot -# tracer: nop -# -# entries-in-buffer/entries-written: 71/71 #P:8 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - <idle>-0 [005] d... 2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120 - sleep-2242 [005] d... 2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120 -[...] - <idle>-0 [002] d... 2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120 - - # cat trace -# tracer: nop -# -# entries-in-buffer/entries-written: 77/77 #P:8 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - <idle>-0 [007] d... 2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120 - snapshot-test-2-2229 [002] d... 2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120 -[...] - - -If you try to use this snapshot feature when current tracer is -one of the latency tracers, you will get the following results. - - # echo wakeup > current_tracer - # echo 1 > snapshot -bash: echo: write error: Device or resource busy - # cat snapshot -cat: snapshot: Device or resource busy - - -Instances ---------- -In the tracefs tracing directory is a directory called "instances". -This directory can have new directories created inside of it using -mkdir, and removing directories with rmdir. The directory created -with mkdir in this directory will already contain files and other -directories after it is created. - - # mkdir instances/foo - # ls instances/foo -buffer_size_kb buffer_total_size_kb events free_buffer per_cpu -set_event snapshot trace trace_clock trace_marker trace_options -trace_pipe tracing_on - -As you can see, the new directory looks similar to the tracing directory -itself. In fact, it is very similar, except that the buffer and -events are agnostic from the main director, or from any other -instances that are created. - -The files in the new directory work just like the files with the -same name in the tracing directory except the buffer that is used -is a separate and new buffer. The files affect that buffer but do not -affect the main buffer with the exception of trace_options. Currently, -the trace_options affect all instances and the top level buffer -the same, but this may change in future releases. That is, options -may become specific to the instance they reside in. - -Notice that none of the function tracer files are there, nor is -current_tracer and available_tracers. This is because the buffers -can currently only have events enabled for them. - - # mkdir instances/foo - # mkdir instances/bar - # mkdir instances/zoot - # echo 100000 > buffer_size_kb - # echo 1000 > instances/foo/buffer_size_kb - # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb - # echo function > current_trace - # echo 1 > instances/foo/events/sched/sched_wakeup/enable - # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable - # echo 1 > instances/foo/events/sched/sched_switch/enable - # echo 1 > instances/bar/events/irq/enable - # echo 1 > instances/zoot/events/syscalls/enable - # cat trace_pipe -CPU:2 [LOST 11745 EVENTS] - bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist - bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave - bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist - bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist - bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock - bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype - bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist - bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist - bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics - bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics - bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process -[...] - - # cat instances/foo/trace_pipe - bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 - bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 - <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003 - <idle>-0 [003] d..3 136.676909: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=9 next_prio=120 - rcu_preempt-9 [003] d..3 136.676916: sched_switch: prev_comm=rcu_preempt prev_pid=9 prev_prio=120 prev_state=S ==> next_comm=swapper/3 next_pid=0 next_prio=120 - bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 - bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 - bash-1998 [000] d..3 136.677018: sched_switch: prev_comm=bash prev_pid=1998 prev_prio=120 prev_state=R+ ==> next_comm=kworker/0:1 next_pid=59 next_prio=120 - kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001 - kworker/0:1-59 [000] d..3 136.677025: sched_switch: prev_comm=kworker/0:1 prev_pid=59 prev_prio=120 prev_state=S ==> next_comm=bash next_pid=1998 next_prio=120 -[...] - - # cat instances/bar/trace_pipe - migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX] - <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX] - bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER] - bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU] - bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER] - bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER] - bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU] - bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU] - sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4 - sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled - sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0 - sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled -[...] - - # cat instances/zoot/trace -# tracer: nop -# -# entries-in-buffer/entries-written: 18996/18996 #P:4 -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - bash-1998 [000] d... 140.733501: sys_write -> 0x2 - bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1) - bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1 - bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0) - bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1 - bash-1998 [000] d... 140.733510: sys_close(fd: a) - bash-1998 [000] d... 140.733510: sys_close -> 0x0 - bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8) - bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0 - bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8) - bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0 - -You can see that the trace of the top most trace buffer shows only -the function tracing. The foo instance displays wakeups and task -switches. - -To remove the instances, simply delete their directories: - - # rmdir instances/foo - # rmdir instances/bar - # rmdir instances/zoot - -Note, if a process has a trace file open in one of the instance -directories, the rmdir will fail with EBUSY. - - -Stack trace ------------ -Since the kernel has a fixed sized stack, it is important not to -waste it in functions. A kernel developer must be conscience of -what they allocate on the stack. If they add too much, the system -can be in danger of a stack overflow, and corruption will occur, -usually leading to a system panic. - -There are some tools that check this, usually with interrupts -periodically checking usage. But if you can perform a check -at every function call that will become very useful. As ftrace provides -a function tracer, it makes it convenient to check the stack size -at every function call. This is enabled via the stack tracer. - -CONFIG_STACK_TRACER enables the ftrace stack tracing functionality. -To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled. - - # echo 1 > /proc/sys/kernel/stack_tracer_enabled - -You can also enable it from the kernel command line to trace -the stack size of the kernel during boot up, by adding "stacktrace" -to the kernel command line parameter. - -After running it for a few minutes, the output looks like: - - # cat stack_max_size -2928 - - # cat stack_trace - Depth Size Location (18 entries) - ----- ---- -------- - 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac - 1) 2704 160 find_busiest_group+0x31/0x1f1 - 2) 2544 256 load_balance+0xd9/0x662 - 3) 2288 80 idle_balance+0xbb/0x130 - 4) 2208 128 __schedule+0x26e/0x5b9 - 5) 2080 16 schedule+0x64/0x66 - 6) 2064 128 schedule_timeout+0x34/0xe0 - 7) 1936 112 wait_for_common+0x97/0xf1 - 8) 1824 16 wait_for_completion+0x1d/0x1f - 9) 1808 128 flush_work+0xfe/0x119 - 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20 - 11) 1664 48 input_available_p+0x1d/0x5c - 12) 1616 48 n_tty_poll+0x6d/0x134 - 13) 1568 64 tty_poll+0x64/0x7f - 14) 1504 880 do_select+0x31e/0x511 - 15) 624 400 core_sys_select+0x177/0x216 - 16) 224 96 sys_select+0x91/0xb9 - 17) 128 128 system_call_fastpath+0x16/0x1b - -Note, if -mfentry is being used by gcc, functions get traced before -they set up the stack frame. This means that leaf level functions -are not tested by the stack tracer when -mfentry is used. - -Currently, -mfentry is used by gcc 4.6.0 and above on x86 only. - ---------- - -More details can be found in the source code, in the -kernel/trace/*.c files. diff --git a/Documentation/trace/hwlat_detector.txt b/Documentation/trace/hwlat_detector.rst index 3207717a0d1a..5739349649c8 100644 --- a/Documentation/trace/hwlat_detector.txt +++ b/Documentation/trace/hwlat_detector.rst @@ -1,4 +1,8 @@ -Introduction: +========================= +Hardware Latency Detector +========================= + +Introduction ------------- The tracer hwlat_detector is a special purpose tracer that is used to @@ -28,7 +32,7 @@ Note that the hwlat detector should *NEVER* be used in a production environment. It is intended to be run manually to determine if the hardware platform has a problem with long system firmware service routines. -Usage: +Usage ------ Write the ASCII text "hwlat" into the current_tracer file of the tracing system @@ -36,16 +40,16 @@ Write the ASCII text "hwlat" into the current_tracer file of the tracing system redefine the threshold in microseconds (us) above which latency spikes will be taken into account. -Example: +Example:: # echo hwlat > /sys/kernel/tracing/current_tracer # echo 100 > /sys/kernel/tracing/tracing_thresh The /sys/kernel/tracing/hwlat_detector interface contains the following files: -width - time period to sample with CPUs held (usecs) - must be less than the total window size (enforced) -window - total period of sampling, width being inside (usecs) + - width - time period to sample with CPUs held (usecs) + must be less than the total window size (enforced) + - window - total period of sampling, width being inside (usecs) By default the width is set to 500,000 and window to 1,000,000, meaning that for every 1,000,000 usecs (1s) the hwlat detector will spin for 500,000 usecs @@ -67,11 +71,11 @@ The following tracing directory files are used by the hwlat_detector: in /sys/kernel/tracing: - tracing_threshold - minimum latency value to be considered (usecs) - tracing_max_latency - maximum hardware latency actually observed (usecs) - tracing_cpumask - the CPUs to move the hwlat thread across - hwlat_detector/width - specified amount of time to spin within window (usecs) - hwlat_detector/window - amount of time between (width) runs (usecs) + - tracing_threshold - minimum latency value to be considered (usecs) + - tracing_max_latency - maximum hardware latency actually observed (usecs) + - tracing_cpumask - the CPUs to move the hwlat thread across + - hwlat_detector/width - specified amount of time to spin within window (usecs) + - hwlat_detector/window - amount of time between (width) runs (usecs) The hwlat detector's kernel thread will migrate across each CPU specified in tracing_cpumask between each window. To limit the migration, either modify diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst new file mode 100644 index 000000000000..b58c10b04e27 --- /dev/null +++ b/Documentation/trace/index.rst @@ -0,0 +1,23 @@ +========================== +Linux Tracing Technologies +========================== + +.. toctree:: + :maxdepth: 2 + + ftrace-design + tracepoint-analysis + ftrace + ftrace-uses + kprobetrace + uprobetracer + tracepoints + events + events-kmem + events-power + events-nmi + events-msr + mmiotrace + hwlat_detector + intel_th + stm diff --git a/Documentation/trace/intel_th.txt b/Documentation/trace/intel_th.rst index 7a57165c2492..990f13265178 100644 --- a/Documentation/trace/intel_th.txt +++ b/Documentation/trace/intel_th.rst @@ -1,3 +1,4 @@ +======================= Intel(R) Trace Hub (TH) ======================= @@ -18,13 +19,13 @@ via sysfs attributes. Currently, the following Intel TH subdevices (blocks) are supported: - Software Trace Hub (STH), trace source, which is a System Trace - Module (STM) device, + Module (STM) device, - Memory Storage Unit (MSU), trace output, which allows storing - trace hub output in system memory, + trace hub output in system memory, - Parallel Trace Interface output (PTI), trace output to an external - debug host via a PTI port, + debug host via a PTI port, - Global Trace Hub (GTH), which is a switch and a central component - of Intel(R) Trace Hub architecture. + of Intel(R) Trace Hub architecture. Common attributes for output devices are described in Documentation/ABI/testing/sysfs-bus-intel_th-output-devices, the most @@ -65,41 +66,41 @@ allocated, are accessible via /dev/intel_th0/msc{0,1}. Quick example ------------- -# figure out which GTH port is the first memory controller: +# figure out which GTH port is the first memory controller:: -$ cat /sys/bus/intel_th/devices/0-msc0/port -0 + $ cat /sys/bus/intel_th/devices/0-msc0/port + 0 -# looks like it's port 0, configure master 33 to send data to port 0: +# looks like it's port 0, configure master 33 to send data to port 0:: -$ echo 0 > /sys/bus/intel_th/devices/0-gth/masters/33 + $ echo 0 > /sys/bus/intel_th/devices/0-gth/masters/33 # allocate a 2-windowed multiblock buffer on the first memory -# controller, each with 64 pages: +# controller, each with 64 pages:: -$ echo multi > /sys/bus/intel_th/devices/0-msc0/mode -$ echo 64,64 > /sys/bus/intel_th/devices/0-msc0/nr_pages + $ echo multi > /sys/bus/intel_th/devices/0-msc0/mode + $ echo 64,64 > /sys/bus/intel_th/devices/0-msc0/nr_pages -# enable wrapping for this controller, too: +# enable wrapping for this controller, too:: -$ echo 1 > /sys/bus/intel_th/devices/0-msc0/wrap + $ echo 1 > /sys/bus/intel_th/devices/0-msc0/wrap -# and enable tracing into this port: +# and enable tracing into this port:: -$ echo 1 > /sys/bus/intel_th/devices/0-msc0/active + $ echo 1 > /sys/bus/intel_th/devices/0-msc0/active # .. send data to master 33, see stm.txt for more details .. # .. wait for traces to pile up .. -# .. and stop the trace: +# .. and stop the trace:: -$ echo 0 > /sys/bus/intel_th/devices/0-msc0/active + $ echo 0 > /sys/bus/intel_th/devices/0-msc0/active -# and now you can collect the trace from the device node: +# and now you can collect the trace from the device node:: -$ cat /dev/intel_th0/msc0 > my_stp_trace + $ cat /dev/intel_th0/msc0 > my_stp_trace Host Debugger Mode -================== +------------------ It is possible to configure the Trace Hub and control its trace capture from a remote debug host, which should be connected via one of diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.rst index 1a3a3d6bc2a8..3e0f971b12de 100644 --- a/Documentation/trace/kprobetrace.txt +++ b/Documentation/trace/kprobetrace.rst @@ -1,8 +1,8 @@ - Kprobe-based Event Tracing - ========================== - - Documentation is written by Masami Hiramatsu +========================== +Kprobe-based Event Tracing +========================== +:Author: Masami Hiramatsu Overview -------- @@ -23,6 +23,8 @@ current_tracer. Instead of that, add probe points via Synopsis of kprobe_events ------------------------- +:: + p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe -:[GRP/]EVENT : Clear a probe @@ -66,7 +68,7 @@ String type is a special type, which fetches a "null-terminated" string from kernel space. This means it will fail and store NULL if the string container has been paged out. Bitfield is another special type, which takes 3 parameters, bit-width, bit- -offset, and container-size (usually 32). The syntax is; +offset, and container-size (usually 32). The syntax is:: b<bit-width>@<bit-offset>/<container-size> @@ -75,7 +77,7 @@ For $comm, the default type is "string"; any other type is invalid. Per-Probe Event Filtering ------------------------- - Per-probe event filtering feature allows you to set different filter on each +Per-probe event filtering feature allows you to set different filter on each probe and gives you what arguments will be shown in trace buffer. If an event name is specified right after 'p:' or 'r:' in kprobe_events, it adds an event under tracing/events/kprobes/<EVENT>, at the directory you can see 'id', @@ -96,87 +98,93 @@ id: Event Profiling --------------- - You can check the total number of probe hits and probe miss-hits via +You can check the total number of probe hits and probe miss-hits via /sys/kernel/debug/tracing/kprobe_profile. - The first column is event name, the second is the number of probe hits, +The first column is event name, the second is the number of probe hits, the third is the number of probe miss-hits. Usage examples -------------- To add a probe as a new event, write a new definition to kprobe_events -as below. +as below:: echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events - This sets a kprobe on the top of do_sys_open() function with recording +This sets a kprobe on the top of do_sys_open() function with recording 1st to 4th arguments as "myprobe" event. Note, which register/stack entry is assigned to each function argument depends on arch-specific ABI. If you unsure the ABI, please try to use probe subcommand of perf-tools (you can find it under tools/perf/). As this example shows, users can choose more familiar names for each arguments. +:: echo 'r:myretprobe do_sys_open $retval' >> /sys/kernel/debug/tracing/kprobe_events - This sets a kretprobe on the return point of do_sys_open() function with +This sets a kretprobe on the return point of do_sys_open() function with recording return value as "myretprobe" event. - You can see the format of these events via +You can see the format of these events via /sys/kernel/debug/tracing/events/kprobes/<EVENT>/format. +:: cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format -name: myprobe -ID: 780 -format: - field:unsigned short common_type; offset:0; size:2; signed:0; - field:unsigned char common_flags; offset:2; size:1; signed:0; - field:unsigned char common_preempt_count; offset:3; size:1;signed:0; - field:int common_pid; offset:4; size:4; signed:1; + name: myprobe + ID: 780 + format: + field:unsigned short common_type; offset:0; size:2; signed:0; + field:unsigned char common_flags; offset:2; size:1; signed:0; + field:unsigned char common_preempt_count; offset:3; size:1;signed:0; + field:int common_pid; offset:4; size:4; signed:1; - field:unsigned long __probe_ip; offset:12; size:4; signed:0; - field:int __probe_nargs; offset:16; size:4; signed:1; - field:unsigned long dfd; offset:20; size:4; signed:0; - field:unsigned long filename; offset:24; size:4; signed:0; - field:unsigned long flags; offset:28; size:4; signed:0; - field:unsigned long mode; offset:32; size:4; signed:0; + field:unsigned long __probe_ip; offset:12; size:4; signed:0; + field:int __probe_nargs; offset:16; size:4; signed:1; + field:unsigned long dfd; offset:20; size:4; signed:0; + field:unsigned long filename; offset:24; size:4; signed:0; + field:unsigned long flags; offset:28; size:4; signed:0; + field:unsigned long mode; offset:32; size:4; signed:0; -print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip, -REC->dfd, REC->filename, REC->flags, REC->mode + print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip, + REC->dfd, REC->filename, REC->flags, REC->mode - You can see that the event has 4 arguments as in the expressions you specified. +You can see that the event has 4 arguments as in the expressions you specified. +:: echo > /sys/kernel/debug/tracing/kprobe_events - This clears all probe points. +This clears all probe points. - Or, +Or, +:: echo -:myprobe >> kprobe_events - This clears probe points selectively. +This clears probe points selectively. - Right after definition, each event is disabled by default. For tracing these +Right after definition, each event is disabled by default. For tracing these events, you need to enable it. +:: echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable - And you can see the traced information via /sys/kernel/debug/tracing/trace. +And you can see the traced information via /sys/kernel/debug/tracing/trace. +:: cat /sys/kernel/debug/tracing/trace -# tracer: nop -# -# TASK-PID CPU# TIMESTAMP FUNCTION -# | | | | | - <...>-1447 [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0 - <...>-1447 [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $retval=fffffffffffffffe - <...>-1447 [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6 - <...>-1447 [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 - <...>-1447 [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10 - <...>-1447 [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 - - - Each line shows when the kernel hits an event, and <- SYMBOL means kernel + # tracer: nop + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + <...>-1447 [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0 + <...>-1447 [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $retval=fffffffffffffffe + <...>-1447 [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6 + <...>-1447 [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 + <...>-1447 [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10 + <...>-1447 [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 + + +Each line shows when the kernel hits an event, and <- SYMBOL means kernel returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel returns from do_sys_open to sys_open+0x1b). diff --git a/Documentation/trace/mmiotrace.txt b/Documentation/trace/mmiotrace.rst index 664e7386d89e..5116e8ca27b4 100644 --- a/Documentation/trace/mmiotrace.txt +++ b/Documentation/trace/mmiotrace.rst @@ -1,4 +1,6 @@ - In-kernel memory-mapped I/O tracing +=================================== +In-kernel memory-mapped I/O tracing +=================================== Home page and links to optional user space tools: @@ -31,30 +33,35 @@ is no way to automatically detect if you are losing events due to CPUs racing. Usage Quick Reference --------------------- +:: -$ mount -t debugfs debugfs /sys/kernel/debug -$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer -$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt & -Start X or whatever. -$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker -$ echo nop > /sys/kernel/debug/tracing/current_tracer -Check for lost events. + $ mount -t debugfs debugfs /sys/kernel/debug + $ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer + $ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt & + Start X or whatever. + $ echo "X is up" > /sys/kernel/debug/tracing/trace_marker + $ echo nop > /sys/kernel/debug/tracing/current_tracer + Check for lost events. Usage ----- Make sure debugfs is mounted to /sys/kernel/debug. -If not (requires root privileges): -$ mount -t debugfs debugfs /sys/kernel/debug +If not (requires root privileges):: + + $ mount -t debugfs debugfs /sys/kernel/debug Check that the driver you are about to trace is not loaded. -Activate mmiotrace (requires root privileges): -$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer +Activate mmiotrace (requires root privileges):: + + $ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer + +Start storing the trace:: + + $ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt & -Start storing the trace: -$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt & The 'cat' process should stay running (sleeping) in the background. Load the driver you want to trace and use it. Mmiotrace will only catch MMIO @@ -66,30 +73,42 @@ This makes it easier to see which part of the (huge) trace corresponds to which action. It is recommended to place descriptive markers about what you do. -Shut down mmiotrace (requires root privileges): -$ echo nop > /sys/kernel/debug/tracing/current_tracer +Shut down mmiotrace (requires root privileges):: + + $ echo nop > /sys/kernel/debug/tracing/current_tracer + The 'cat' process exits. If it does not, kill it by issuing 'fg' command and pressing ctrl+c. -Check that mmiotrace did not lose events due to a buffer filling up. Either -$ grep -i lost mydump.txt -which tells you exactly how many events were lost, or use -$ dmesg +Check that mmiotrace did not lose events due to a buffer filling up. Either:: + + $ grep -i lost mydump.txt + +which tells you exactly how many events were lost, or use:: + + $ dmesg + to view your kernel log and look for "mmiotrace has lost events" warning. If events were lost, the trace is incomplete. You should enlarge the buffers and try again. Buffers are enlarged by first seeing how large the current buffers -are: -$ cat /sys/kernel/debug/tracing/buffer_size_kb +are:: + + $ cat /sys/kernel/debug/tracing/buffer_size_kb + gives you a number. Approximately double this number and write it back, for -instance: -$ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb +instance:: + + $ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb + Then start again from the top. If you are doing a trace for a driver project, e.g. Nouveau, you should also -do the following before sending your results: -$ lspci -vvv > lspci.txt -$ dmesg > dmesg.txt -$ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt +do the following before sending your results:: + + $ lspci -vvv > lspci.txt + $ dmesg > dmesg.txt + $ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt + and then send the .tar.gz file. The trace compresses considerably. Replace "pciid" and "nick" with the PCI ID or model name of your piece of hardware under investigation and your nickname. @@ -148,17 +167,18 @@ zero if it is not recorded. PID is always zero as tracing MMIO accesses originating in user space memory is not yet supported. For instance, the following awk filter will pass all 32-bit writes that target -physical addresses in the range [0xfb73ce40, 0xfb800000[ +physical addresses in the range [0xfb73ce40, 0xfb800000] +:: -$ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 && -adr < 0xfb800000) print; }' + $ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 && + adr < 0xfb800000) print; }' Tools for Developers -------------------- The user space tools include utilities for: -- replacing numeric addresses and values with hardware register names -- replaying MMIO logs, i.e., re-executing the recorded writes + - replacing numeric addresses and values with hardware register names + - replaying MMIO logs, i.e., re-executing the recorded writes diff --git a/Documentation/trace/stm.txt b/Documentation/trace/stm.rst index 03765750104b..2c22ddb7fd3e 100644 --- a/Documentation/trace/stm.txt +++ b/Documentation/trace/stm.rst @@ -1,3 +1,4 @@ +=================== System Trace Module =================== @@ -32,14 +33,14 @@ associated with it, located in "stp-policy" subsystem directory in configfs. The topmost directory's name (the policy) is formatted as the STM device name to which this policy applies and and arbitrary string identifier separated by a stop. From the examle above, a rule -may look like this: +may look like this:: -$ ls /config/stp-policy/dummy_stm.my-policy/user -channels masters -$ cat /config/stp-policy/dummy_stm.my-policy/user/masters -48 63 -$ cat /config/stp-policy/dummy_stm.my-policy/user/channels -0 127 + $ ls /config/stp-policy/dummy_stm.my-policy/user + channels masters + $ cat /config/stp-policy/dummy_stm.my-policy/user/masters + 48 63 + $ cat /config/stp-policy/dummy_stm.my-policy/user/channels + 0 127 which means that the master allocation pool for this rule consists of masters 48 through 63 and channel allocation pool has channels 0 @@ -78,9 +79,9 @@ stm_source For kernel-based trace sources, there is "stm_source" device class. Devices of this class can be connected and disconnected to/from stm devices at runtime via a sysfs attribute called "stm_source_link" -by writing the name of the desired stm device there, for example: +by writing the name of the desired stm device there, for example:: -$ echo dummy_stm.0 > /sys/class/stm_source/console/stm_source_link + $ echo dummy_stm.0 > /sys/class/stm_source/console/stm_source_link For examples on how to use stm_source interface in the kernel, refer to stm_console, stm_heartbeat or stm_ftrace drivers. @@ -118,5 +119,5 @@ the same time. Currently only Ftrace "function" tracer is supported. -[1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf -[2] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0444b/index.html +* [1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf +* [2] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0444b/index.html diff --git a/Documentation/trace/tracepoint-analysis.txt b/Documentation/trace/tracepoint-analysis.rst index 058cc6c9dc56..a4d3ff2e5efb 100644 --- a/Documentation/trace/tracepoint-analysis.txt +++ b/Documentation/trace/tracepoint-analysis.rst @@ -1,7 +1,7 @@ - Notes on Analysing Behaviour Using Events and Tracepoints - - Documentation written by Mel Gorman - PCL information heavily based on email from Ingo Molnar +========================================================= +Notes on Analysing Behaviour Using Events and Tracepoints +========================================================= +:Author: Mel Gorman (PCL information heavily based on email from Ingo Molnar) 1. Introduction =============== @@ -27,18 +27,18 @@ assumed that the PCL tool tools/perf has been installed and is in your path. ---------------------- All possible events are visible from /sys/kernel/debug/tracing/events. Simply -calling +calling:: $ find /sys/kernel/debug/tracing/events -type d will give a fair indication of the number of events available. 2.2 PCL (Performance Counters for Linux) -------- +---------------------------------------- Discovery and enumeration of all counters and events, including tracepoints, are available with the perf tool. Getting a list of available events is a -simple case of: +simple case of:: $ perf list 2>&1 | grep Tracepoint ext4:ext4_free_inode [Tracepoint event] @@ -57,7 +57,7 @@ simple case of: See Documentation/trace/events.txt for a proper description on how events can be enabled system-wide. A short example of enabling all events related -to page allocation would look something like: +to page allocation would look something like:: $ for i in `find /sys/kernel/debug/tracing/events -name "enable" | grep mm_`; do echo 1 > $i; done @@ -67,6 +67,7 @@ to page allocation would look something like: In SystemTap, tracepoints are accessible using the kernel.trace() function call. The following is an example that reports every 5 seconds what processes were allocating the pages. +:: global page_allocs @@ -91,6 +92,7 @@ were allocating the pages. By specifying the -a switch and analysing sleep, the system-wide events for a duration of time can be examined. +:: $ perf stat -a \ -e kmem:mm_page_alloc -e kmem:mm_page_free \ @@ -118,6 +120,7 @@ basis using set_ftrace_pid. Events can be activated and tracked for the duration of a process on a local basis using PCL such as follows. +:: $ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free \ -e kmem:mm_page_free_batched ./hackbench 10 @@ -145,6 +148,7 @@ Any workload can exhibit variances between runs and it can be important to know what the standard deviation is. By and large, this is left to the performance analyst to do it by hand. In the event that the discrete event occurrences are useful to the performance analyst, then perf can be used. +:: $ perf stat --repeat 5 -e kmem:mm_page_alloc -e kmem:mm_page_free -e kmem:mm_page_free_batched ./hackbench 10 @@ -167,6 +171,7 @@ aggregation of discrete events, then a script would need to be developed. Using --repeat, it is also possible to view how events are fluctuating over time on a system-wide basis using -a and sleep. +:: $ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free \ -e kmem:mm_page_free_batched \ @@ -188,9 +193,9 @@ When events are enabled the events that are triggering can be read from options exist as well. By post-processing the output, further information can be gathered on-line as appropriate. Examples of post-processing might include - o Reading information from /proc for the PID that triggered the event - o Deriving a higher-level event from a series of lower-level events. - o Calculating latencies between two events + - Reading information from /proc for the PID that triggered the event + - Deriving a higher-level event from a series of lower-level events. + - Calculating latencies between two events Documentation/trace/postprocess/trace-pagealloc-postprocess.pl is an example script that can read trace_pipe from STDIN or a copy of a trace. When used @@ -200,14 +205,14 @@ and twice to exit. Simplistically, the script just reads STDIN and counts up events but it also can do more such as - o Derive high-level events from many low-level events. If a number of pages + - Derive high-level events from many low-level events. If a number of pages are freed to the main allocator from the per-CPU lists, it recognises that as one per-CPU drain even though there is no specific tracepoint for that event - o It can aggregate based on PID or individual process number - o In the event memory is getting externally fragmented, it reports + - It can aggregate based on PID or individual process number + - In the event memory is getting externally fragmented, it reports on whether the fragmentation event was severe or moderate. - o When receiving an event about a PID, it can record who the parent was so + - When receiving an event about a PID, it can record who the parent was so that if large numbers of events are coming from very short-lived processes, the parent process responsible for creating all the helpers can be identified @@ -218,6 +223,7 @@ also can do more such as There may also be a requirement to identify what functions within a program were generating events within the kernel. To begin this sort of analysis, the data must be recorded. At the time of writing, this required root: +:: $ perf record -c 1 \ -e kmem:mm_page_alloc -e kmem:mm_page_free \ @@ -232,6 +238,7 @@ very coarse as a result. This record outputted a file called perf.data which can be analysed using perf report. +:: $ perf report # Samples: 30922 @@ -258,6 +265,7 @@ within the VDSO. With simple binaries, this will often be the case so let's take a slightly different example. In the course of writing this, it was noticed that X was generating an insane amount of page allocations so let's look at it: +:: $ perf record -c 1 -f \ -e kmem:mm_page_alloc -e kmem:mm_page_free \ @@ -265,6 +273,7 @@ at it: -p `pidof X` This was interrupted after a few seconds and +:: $ perf report # Samples: 27666 @@ -282,6 +291,7 @@ This was interrupted after a few seconds and So, almost half of the events are occurring in a library. To get an idea which symbol: +:: $ perf report --sort comm,dso,symbol # Samples: 27666 @@ -298,6 +308,7 @@ symbol: 0.00% Xorg [kernel] [k] ftrace_trace_userstack To see where within the function pixmanFillsse2 things are going wrong: +:: $ perf annotate pixmanFillsse2 [ ... ] diff --git a/Documentation/trace/tracepoints.txt b/Documentation/trace/tracepoints.rst index a3efac621c5a..6e3ce3bf3593 100644 --- a/Documentation/trace/tracepoints.txt +++ b/Documentation/trace/tracepoints.rst @@ -1,6 +1,8 @@ - Using the Linux Kernel Tracepoints +================================== +Using the Linux Kernel Tracepoints +================================== - Mathieu Desnoyers +:Author: Mathieu Desnoyers This document introduces Linux Kernel Tracepoints and their use. It @@ -9,8 +11,8 @@ connect probe functions to them and provides some examples of probe functions. -* Purpose of tracepoints - +Purpose of tracepoints +---------------------- A tracepoint placed in code provides a hook to call a function (probe) that you can provide at runtime. A tracepoint can be "on" (a probe is connected to it) or "off" (no probe is attached). When a tracepoint is @@ -31,8 +33,8 @@ header file. They can be used for tracing and performance accounting. -* Usage - +Usage +----- Two elements are required for tracepoints : - A tracepoint definition, placed in a header file. @@ -40,52 +42,53 @@ Two elements are required for tracepoints : In order to use tracepoints, you should include linux/tracepoint.h. -In include/trace/events/subsys.h : +In include/trace/events/subsys.h:: -#undef TRACE_SYSTEM -#define TRACE_SYSTEM subsys + #undef TRACE_SYSTEM + #define TRACE_SYSTEM subsys -#if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) -#define _TRACE_SUBSYS_H + #if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) + #define _TRACE_SUBSYS_H -#include <linux/tracepoint.h> + #include <linux/tracepoint.h> -DECLARE_TRACE(subsys_eventname, - TP_PROTO(int firstarg, struct task_struct *p), - TP_ARGS(firstarg, p)); + DECLARE_TRACE(subsys_eventname, + TP_PROTO(int firstarg, struct task_struct *p), + TP_ARGS(firstarg, p)); -#endif /* _TRACE_SUBSYS_H */ + #endif /* _TRACE_SUBSYS_H */ -/* This part must be outside protection */ -#include <trace/define_trace.h> + /* This part must be outside protection */ + #include <trace/define_trace.h> -In subsys/file.c (where the tracing statement must be added) : +In subsys/file.c (where the tracing statement must be added):: -#include <trace/events/subsys.h> + #include <trace/events/subsys.h> -#define CREATE_TRACE_POINTS -DEFINE_TRACE(subsys_eventname); + #define CREATE_TRACE_POINTS + DEFINE_TRACE(subsys_eventname); -void somefct(void) -{ - ... - trace_subsys_eventname(arg, task); - ... -} + void somefct(void) + { + ... + trace_subsys_eventname(arg, task); + ... + } Where : -- subsys_eventname is an identifier unique to your event + - subsys_eventname is an identifier unique to your event + - subsys is the name of your subsystem. - eventname is the name of the event to trace. -- TP_PROTO(int firstarg, struct task_struct *p) is the prototype of the - function called by this tracepoint. + - `TP_PROTO(int firstarg, struct task_struct *p)` is the prototype of the + function called by this tracepoint. -- TP_ARGS(firstarg, p) are the parameters names, same as found in the - prototype. + - `TP_ARGS(firstarg, p)` are the parameters names, same as found in the + prototype. -- if you use the header in multiple source files, #define CREATE_TRACE_POINTS - should appear only in one source file. + - if you use the header in multiple source files, `#define CREATE_TRACE_POINTS` + should appear only in one source file. Connecting a function (probe) to a tracepoint is done by providing a probe (function to call) for the specific tracepoint through @@ -117,7 +120,7 @@ used to export the defined tracepoints. If you need to do a bit of work for a tracepoint parameter, and that work is only used for the tracepoint, that work can be encapsulated -within an if statement with the following: +within an if statement with the following:: if (trace_foo_bar_enabled()) { int i; @@ -139,7 +142,7 @@ The advantage of using the trace_<tracepoint>_enabled() is that it uses the static_key of the tracepoint to allow the if statement to be implemented with jump labels and avoid conditional branches. -Note: The convenience macro TRACE_EVENT provides an alternative way to +.. note:: The convenience macro TRACE_EVENT provides an alternative way to define tracepoints. Check http://lwn.net/Articles/379903, http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362 for a series of articles with more details. diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.rst index bf526a7c5559..98d3f692957a 100644 --- a/Documentation/trace/uprobetracer.txt +++ b/Documentation/trace/uprobetracer.rst @@ -1,7 +1,8 @@ - Uprobe-tracer: Uprobe-based Event Tracing - ========================================= +========================================= +Uprobe-tracer: Uprobe-based Event Tracing +========================================= - Documentation written by Srikar Dronamraju +:Author: Srikar Dronamraju Overview @@ -19,6 +20,8 @@ user to calculate the offset of the probepoint in the object. Synopsis of uprobe_tracer ------------------------- +:: + p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe) -:[GRP/]EVENT : Clear uprobe or uretprobe event @@ -57,7 +60,7 @@ x86-64 uses x64). String type is a special type, which fetches a "null-terminated" string from user space. Bitfield is another special type, which takes 3 parameters, bit-width, bit- -offset, and container-size (usually 32). The syntax is; +offset, and container-size (usually 32). The syntax is:: b<bit-width>@<bit-offset>/<container-size> @@ -74,28 +77,28 @@ the third is the number of probe miss-hits. Usage examples -------------- * Add a probe as a new uprobe event, write a new definition to uprobe_events -as below: (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash) + as below (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash):: echo 'p /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events - * Add a probe as a new uretprobe event: + * Add a probe as a new uretprobe event:: echo 'r /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events - * Unset registered event: + * Unset registered event:: echo '-:p_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events - * Print out the events that are registered: + * Print out the events that are registered:: cat /sys/kernel/debug/tracing/uprobe_events - * Clear all events: + * Clear all events:: echo > /sys/kernel/debug/tracing/uprobe_events Following example shows how to dump the instruction pointer and %ax register -at the probed text address. Probe zfree function in /bin/zsh: +at the probed text address. Probe zfree function in /bin/zsh:: # cd /sys/kernel/debug/tracing/ # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp @@ -103,24 +106,27 @@ at the probed text address. Probe zfree function in /bin/zsh: # objdump -T /bin/zsh | grep -w zfree 0000000000446420 g DF .text 0000000000000012 Base zfree - 0x46420 is the offset of zfree in object /bin/zsh that is loaded at - 0x00400000. Hence the command to uprobe would be: +0x46420 is the offset of zfree in object /bin/zsh that is loaded at +0x00400000. Hence the command to uprobe would be:: # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events - And the same for the uretprobe would be: +And the same for the uretprobe would be:: # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events -Please note: User has to explicitly calculate the offset of the probe-point -in the object. We can see the events that are registered by looking at the -uprobe_events file. +.. note:: User has to explicitly calculate the offset of the probe-point + in the object. + +We can see the events that are registered by looking at the uprobe_events file. +:: # cat uprobe_events p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax -Format of events can be seen by viewing the file events/uprobes/zfree_entry/format +Format of events can be seen by viewing the file events/uprobes/zfree_entry/format. +:: # cat events/uprobes/zfree_entry/format name: zfree_entry @@ -139,16 +145,18 @@ Format of events can be seen by viewing the file events/uprobes/zfree_entry/form print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2 Right after definition, each event is disabled by default. For tracing these -events, you need to enable it by: +events, you need to enable it by:: # echo 1 > events/uprobes/enable Lets disable the event after sleeping for some time. +:: # sleep 20 # echo 0 > events/uprobes/enable And you can see the traced information via /sys/kernel/debug/tracing/trace. +:: # cat trace # tracer: nop |