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Diffstat (limited to 'Documentation/trace/histogram.rst')
| -rw-r--r-- | Documentation/trace/histogram.rst | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst index 63e522107e59..353317bc3825 100644 --- a/Documentation/trace/histogram.rst +++ b/Documentation/trace/histogram.rst @@ -1874,6 +1874,7 @@ The available actions are: - <synthetic_event_name>(param list) - generate synthetic event - save(field,...) - save current event fields + - snapshot() - snapshot the trace buffer The following commonly-used handler.action pairs are available: @@ -2030,6 +2031,115 @@ The following commonly-used handler.action pairs are available: Entries: 2 Dropped: 0 + - onmax(var).snapshot() + + The 'onmax(var).snapshot()' hist trigger action is invoked + whenever the value of 'var' associated with a histogram entry + exceeds the current maximum contained in that variable. + + The end result is that a global snapshot of the trace buffer will + be saved in the tracing/snapshot file if 'var' exceeds the current + maximum for any hist trigger entry. + + Note that in this case the maximum is a global maximum for the + current trace instance, which is the maximum across all buckets of + the histogram. The key of the specific trace event that caused + the global maximum and the global maximum itself are displayed, + along with a message stating that a snapshot has been taken and + where to find it. The user can use the key information displayed + to locate the corresponding bucket in the histogram for even more + detail. + + As an example the below defines a couple of hist triggers, one for + sched_waking and another for sched_switch, keyed on pid. Whenever + a sched_waking event occurs, the timestamp is saved in the entry + corresponding to the current pid, and when the scheduler switches + back to that pid, the timestamp difference is calculated. If the + resulting latency, stored in wakeup_lat, exceeds the current + maximum latency, a snapshot is taken. As part of the setup, all + the scheduler events are also enabled, which are the events that + will show up in the snapshot when it is taken at some point: + + # echo 1 > /sys/kernel/debug/tracing/events/sched/enable + + # echo 'hist:keys=pid:ts0=common_timestamp.usecs \ + if comm=="cyclictest"' >> \ + /sys/kernel/debug/tracing/events/sched/sched_waking/trigger + + # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0: \ + onmax($wakeup_lat).save(next_prio,next_comm,prev_pid,prev_prio, \ + prev_comm):onmax($wakeup_lat).snapshot() \ + if next_comm=="cyclictest"' >> \ + /sys/kernel/debug/tracing/events/sched/sched_switch/trigger + + When the histogram is displayed, for each bucket the max value + and the saved values corresponding to the max are displayed + following the rest of the fields. + + If a snaphot was taken, there is also a message indicating that, + along with the value and event that triggered the global maximum: + + # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist + { next_pid: 2101 } hitcount: 200 + max: 52 next_prio: 120 next_comm: cyclictest \ + prev_pid: 0 prev_prio: 120 prev_comm: swapper/6 + + { next_pid: 2103 } hitcount: 1326 + max: 572 next_prio: 19 next_comm: cyclictest \ + prev_pid: 0 prev_prio: 120 prev_comm: swapper/1 + + { next_pid: 2102 } hitcount: 1982 \ + max: 74 next_prio: 19 next_comm: cyclictest \ + prev_pid: 0 prev_prio: 120 prev_comm: swapper/5 + + Snapshot taken (see tracing/snapshot). Details: + triggering value { onmax($wakeup_lat) }: 572 \ + triggered by event with key: { next_pid: 2103 } + + Totals: + Hits: 3508 + Entries: 3 + Dropped: 0 + + In the above case, the event that triggered the global maximum has + the key with next_pid == 2103. If you look at the bucket that has + 2103 as the key, you'll find the additional values save()'d along + with the local maximum for that bucket, which should be the same + as the global maximum (since that was the same value that + triggered the global snapshot). + + And finally, looking at the snapshot data should show at or near + the end the event that triggered the snapshot (in this case you + can verify the timestamps between the sched_waking and + sched_switch events, which should match the time displayed in the + global maximum): + + # cat /sys/kernel/debug/tracing/snapshot + + <...>-2103 [005] d..3 309.873125: sched_switch: prev_comm=cyclictest prev_pid=2103 prev_prio=19 prev_state=D ==> next_comm=swapper/5 next_pid=0 next_prio=120 + <idle>-0 [005] d.h3 309.873611: sched_waking: comm=cyclictest pid=2102 prio=19 target_cpu=005 + <idle>-0 [005] dNh4 309.873613: sched_wakeup: comm=cyclictest pid=2102 prio=19 target_cpu=005 + <idle>-0 [005] d..3 309.873616: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=cyclictest next_pid=2102 next_prio=19 + <...>-2102 [005] d..3 309.873625: sched_switch: prev_comm=cyclictest prev_pid=2102 prev_prio=19 prev_state=D ==> next_comm=swapper/5 next_pid=0 next_prio=120 + <idle>-0 [005] d.h3 309.874624: sched_waking: comm=cyclictest pid=2102 prio=19 target_cpu=005 + <idle>-0 [005] dNh4 309.874626: sched_wakeup: comm=cyclictest pid=2102 prio=19 target_cpu=005 + <idle>-0 [005] dNh3 309.874628: sched_waking: comm=cyclictest pid=2103 prio=19 target_cpu=005 + <idle>-0 [005] dNh4 309.874630: sched_wakeup: comm=cyclictest pid=2103 prio=19 target_cpu=005 + <idle>-0 [005] d..3 309.874633: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=cyclictest next_pid=2102 next_prio=19 + <idle>-0 [004] d.h3 309.874757: sched_waking: comm=gnome-terminal- pid=1699 prio=120 target_cpu=004 + <idle>-0 [004] dNh4 309.874762: sched_wakeup: comm=gnome-terminal- pid=1699 prio=120 target_cpu=004 + <idle>-0 [004] d..3 309.874766: sched_switch: prev_comm=swapper/4 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=gnome-terminal- next_pid=1699 next_prio=120 + gnome-terminal--1699 [004] d.h2 309.874941: sched_stat_runtime: comm=gnome-terminal- pid=1699 runtime=180706 [ns] vruntime=1126870572 [ns] + <idle>-0 [003] d.s4 309.874956: sched_waking: comm=rcu_sched pid=9 prio=120 target_cpu=007 + <idle>-0 [003] d.s5 309.874960: sched_wake_idle_without_ipi: cpu=7 + <idle>-0 [003] d.s5 309.874961: sched_wakeup: comm=rcu_sched pid=9 prio=120 target_cpu=007 + <idle>-0 [007] d..3 309.874963: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=rcu_sched next_pid=9 next_prio=120 + rcu_sched-9 [007] d..3 309.874973: sched_stat_runtime: comm=rcu_sched pid=9 runtime=13646 [ns] vruntime=22531430286 [ns] + rcu_sched-9 [007] d..3 309.874978: sched_switch: prev_comm=rcu_sched prev_pid=9 prev_prio=120 prev_state=R+ ==> next_comm=swapper/7 next_pid=0 next_prio=120 + <...>-2102 [005] d..4 309.874994: sched_migrate_task: comm=cyclictest pid=2103 prio=19 orig_cpu=5 dest_cpu=1 + <...>-2102 [005] d..4 309.875185: sched_wake_idle_without_ipi: cpu=1 + <idle>-0 [001] d..3 309.875200: sched_switch: prev_comm=swapper/1 prev_pid=0 prev_prio=120 prev_state=S ==> next_comm=cyclictest next_pid=2103 next_prio=19 + 3. User space creating a trigger -------------------------------- |