forked from Minki/linux
df337d014b
Man page for rtla timerlat top mode. Link: https://lkml.kernel.org/r/58c3d6212e6c6f1f012deb2e998dd082da92075f.1639158831.git.bristot@kernel.org Cc: Tao Zhou <tao.zhou@linux.dev> Cc: Ingo Molnar <mingo@redhat.com> Cc: Tom Zanussi <zanussi@kernel.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Clark Williams <williams@redhat.com> Cc: John Kacur <jkacur@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: linux-rt-users@vger.kernel.org Cc: linux-trace-devel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
146 lines
6.8 KiB
ReStructuredText
146 lines
6.8 KiB
ReStructuredText
====================
|
|
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
|