From patchwork Tue Jan 11 17:30:59 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 531361 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58627C433F5 for ; Tue, 11 Jan 2022 17:31:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344726AbiAKRb5 (ORCPT ); Tue, 11 Jan 2022 12:31:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42896 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344422AbiAKRbW (ORCPT ); Tue, 11 Jan 2022 12:31:22 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 637A8C06175E; Tue, 11 Jan 2022 09:31:20 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id B17DCB81C48; Tue, 11 Jan 2022 17:31:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 627C5C36AED; Tue, 11 Jan 2022 17:31:19 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.95) (envelope-from ) id 1n7KzO-0032K5-Ir; Tue, 11 Jan 2022 12:31:18 -0500 Message-ID: <20220111173118.415962778@goodmis.org> User-Agent: quilt/0.66 Date: Tue, 11 Jan 2022 12:30:59 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , Tao Zhou , Ingo Molnar , Tom Zanussi , Masami Hiramatsu , Juri Lelli , Clark Williams , John Kacur , Peter Zijlstra , Thomas Gleixner , Sebastian Andrzej Siewior , Daniel Bristot de Oliveira , linux-rt-users@vger.kernel.org, linux-trace-devel@vger.kernel.org Subject: [for-next][PATCH 28/31] rtla: Add rtla timerlat top documentation References: <20220111173030.999527342@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org From: Daniel Bristot de Oliveira Man page for rtla timerlat top mode. Link: https://lkml.kernel.org/r/df06fa7801571078e43d77002c6645bdc49f779a.1638182284.git.bristot@kernel.org Cc: Tao Zhou Cc: Ingo Molnar Cc: Tom Zanussi Cc: Masami Hiramatsu Cc: Juri Lelli Cc: Clark Williams Cc: John Kacur Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Sebastian Andrzej Siewior Cc: Daniel Bristot de Oliveira 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 Signed-off-by: Steven Rostedt --- .../tools/rtla/common_timerlat_options.rst | 16 ++ .../tools/rtla/rtla-timerlat-top.rst | 145 ++++++++++++++++++ 2 files changed, 161 insertions(+) create mode 100644 Documentation/tools/rtla/common_timerlat_options.rst create mode 100644 Documentation/tools/rtla/rtla-timerlat-top.rst diff --git a/Documentation/tools/rtla/common_timerlat_options.rst b/Documentation/tools/rtla/common_timerlat_options.rst new file mode 100644 index 000000000000..e9c1bfd55d48 --- /dev/null +++ b/Documentation/tools/rtla/common_timerlat_options.rst @@ -0,0 +1,16 @@ +**-p**, **--period** *us* + + Set the *timerlat* tracer period in microseconds. + +**-i**, **--irq** *us* + + Stop trace if the *IRQ* latency is higher than the argument in us. + +**-T**, **--thread** *us* + + Stop trace if the *Thread* latency is higher than the argument in us. + +**-s**, **--stack** *us* + + Save the stack trace at the *IRQ* if a *Thread* latency is higher than the + argument in us. 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: + => 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: + +AUTHOR +------ +Written by Daniel Bristot de Oliveira + +.. include:: common_appendix.rst