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diff --git a/Documentation/tools/rtla/rtla-timerlat-top.rst b/Documentation/tools/rtla/rtla-timerlat-top.rst new file mode 100644 index 000000000000..1c321de1c171 --- /dev/null +++ b/Documentation/tools/rtla/rtla-timerlat-top.rst @@ -0,0 +1,145 @@ +==================== +rtla-timerlat-top +==================== +------------------------------------------- +Measures the operating system timer latency +------------------------------------------- + +:Manual section: 1 + +SYNOPSIS +======== +**rtla timerlat top** [*OPTIONS*] ... + +DESCRIPTION +=========== + +.. include:: common_timerlat_description.rst + +The **rtla timerlat top** displays a summary of the periodic output +from the *timerlat* tracer. It also provides information for each +operating system noise via the **osnoise:** tracepoints that can be +seem with the option **-T**. + +OPTIONS +======= + +.. include:: common_timerlat_options.rst + +.. include:: common_top_options.rst + +.. include:: common_options.rst + +EXAMPLE +======= + +In the example below, the *timerlat* tracer is set to capture the stack trace at +the IRQ handler, printing it to the buffer if the *Thread* timer latency is +higher than *30 us*. It is also set to stop the session if a *Thread* timer +latency higher than *30 us* is hit. Finally, it is set to save the trace +buffer if the stop condition is hit:: + + [root@alien ~]# rtla timerlat top -s 30 -t 30 -T + Timer Latency + 0 00:00:59 | IRQ Timer Latency (us) | Thread Timer Latency (us) + CPU COUNT | cur min avg max | cur min avg max + 0 #58634 | 1 0 1 10 | 11 2 10 23 + 1 #58634 | 1 0 1 9 | 12 2 9 23 + 2 #58634 | 0 0 1 11 | 10 2 9 23 + 3 #58634 | 1 0 1 11 | 11 2 9 24 + 4 #58634 | 1 0 1 10 | 11 2 9 26 + 5 #58634 | 1 0 1 8 | 10 2 9 25 + 6 #58634 | 12 0 1 12 | 30 2 10 30 <--- CPU with spike + 7 #58634 | 1 0 1 9 | 11 2 9 23 + 8 #58633 | 1 0 1 9 | 11 2 9 26 + 9 #58633 | 1 0 1 9 | 10 2 9 26 + 10 #58633 | 1 0 1 13 | 11 2 9 28 + 11 #58633 | 1 0 1 13 | 12 2 9 24 + 12 #58633 | 1 0 1 8 | 10 2 9 23 + 13 #58633 | 1 0 1 10 | 10 2 9 22 + 14 #58633 | 1 0 1 18 | 12 2 9 27 + 15 #58633 | 1 0 1 10 | 11 2 9 28 + 16 #58633 | 0 0 1 11 | 7 2 9 26 + 17 #58633 | 1 0 1 13 | 10 2 9 24 + 18 #58633 | 1 0 1 9 | 13 2 9 22 + 19 #58633 | 1 0 1 10 | 11 2 9 23 + 20 #58633 | 1 0 1 12 | 11 2 9 28 + 21 #58633 | 1 0 1 14 | 11 2 9 24 + 22 #58633 | 1 0 1 8 | 11 2 9 22 + 23 #58633 | 1 0 1 10 | 11 2 9 27 + timerlat hit stop tracing + saving trace to timerlat_trace.txt + [root@alien bristot]# tail -60 timerlat_trace.txt + [...] + timerlat/5-79755 [005] ....... 426.271226: #58634 context thread timer_latency 10823 ns + sh-109404 [006] dnLh213 426.271247: #58634 context irq timer_latency 12505 ns + sh-109404 [006] dNLh313 426.271258: irq_noise: local_timer:236 start 426.271245463 duration 12553 ns + sh-109404 [006] d...313 426.271263: thread_noise: sh:109404 start 426.271245853 duration 4769 ns + timerlat/6-79756 [006] ....... 426.271264: #58634 context thread timer_latency 30328 ns + timerlat/6-79756 [006] ....1.. 426.271265: <stack trace> + => timerlat_irq + => __hrtimer_run_queues + => hrtimer_interrupt + => __sysvec_apic_timer_interrupt + => sysvec_apic_timer_interrupt + => asm_sysvec_apic_timer_interrupt + => _raw_spin_unlock_irqrestore <---- spinlock that disabled interrupt. + => try_to_wake_up + => autoremove_wake_function + => __wake_up_common + => __wake_up_common_lock + => ep_poll_callback + => __wake_up_common + => __wake_up_common_lock + => fsnotify_add_event + => inotify_handle_inode_event + => fsnotify + => __fsnotify_parent + => __fput + => task_work_run + => exit_to_user_mode_prepare + => syscall_exit_to_user_mode + => do_syscall_64 + => entry_SYSCALL_64_after_hwframe + => 0x7265000001378c + => 0x10000cea7 + => 0x25a00000204a + => 0x12e302d00000000 + => 0x19b51010901b6 + => 0x283ce00726500 + => 0x61ea308872 + => 0x00000fe3 + bash-109109 [007] d..h... 426.271265: #58634 context irq timer_latency 1211 ns + timerlat/6-79756 [006] ....... 426.271267: timerlat_main: stop tracing hit on cpu 6 + +In the trace, it is possible the notice that the *IRQ* timer latency was +already high, accounting *12505 ns*. The IRQ delay was caused by the +*bash-109109* process that disabled IRQs in the wake-up path +(*_try_to_wake_up()* function). The duration of the IRQ handler that woke +up the timerlat thread, informed with the **osnoise:irq_noise** event, was +also high and added more *12553 ns* to the Thread latency. Finally, the +**osnoise:thread_noise** added by the currently running thread (including +the scheduling overhead) added more *4769 ns*. Summing up these values, +the *Thread* timer latency accounted for *30328 ns*. + +The primary reason for this high value is the wake-up path that was hit +twice during this case: when the *bash-109109* was waking up a thread +and then when the *timerlat* thread was awakened. This information can +then be used as the starting point of a more fine-grained analysis. + +Note that **rtla timerlat** was dispatched without changing *timerlat* tracer +threads' priority. That is generally not needed because these threads hava +priority *FIFO:95* by default, which is a common priority used by real-time +kernel developers to analyze scheduling delays. + +SEE ALSO +-------- +**rtla-timerlat**\(1), **rtla-timerlat-hist**\(1) + +*timerlat* tracer documentation: <https://www.kernel.org/doc/html/latest/trace/timerlat-tracer.html> + +AUTHOR +------ +Written by Daniel Bristot de Oliveira <bristot@kernel.org> + +.. include:: common_appendix.rst |