From patchwork Mon Oct 18 16:48:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Bristot de Oliveira X-Patchwork-Id: 12567463 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 282B4C43217 for ; Mon, 18 Oct 2021 16:51:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 14C6461074 for ; Mon, 18 Oct 2021 16:51:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234108AbhJRQxh convert rfc822-to-8bit (ORCPT ); Mon, 18 Oct 2021 12:53:37 -0400 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:53975 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234155AbhJRQxH (ORCPT ); Mon, 18 Oct 2021 12:53:07 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-575-W2aO6ZofNbaSp8pch6bOdg-1; Mon, 18 Oct 2021 12:50:51 -0400 X-MC-Unique: W2aO6ZofNbaSp8pch6bOdg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 403E393C; Mon, 18 Oct 2021 16:50:49 +0000 (UTC) Received: from x1.com (unknown [10.22.18.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7C50E10016F4; Mon, 18 Oct 2021 16:50:46 +0000 (UTC) From: Daniel Bristot de Oliveira To: Steven Rostedt Cc: Daniel Bristot de Oliveira , Ingo Molnar , Tom Zanussi , Masami Hiramatsu , Juri Lelli , Clark Williams , John Kacur , Peter Zijlstra , Thomas Gleixner , Sebastian Andrzej Siewior , linux-rt-users@vger.kernel.org, linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH V3 18/19] rtla: Add rtla timerlat top documentation Date: Mon, 18 Oct 2021 18:48:31 +0200 Message-Id: <81c6fdc36088fccbcd3bfd19b95539704fe4e9a4.1634574261.git.bristot@kernel.org> In-Reply-To: References: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org Man page for rtla timerlat top mode. Cc: Steven Rostedt 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 --- .../rtla/Documentation/rtla-timerlat-top.txt | 181 ++++++++++++++++++ 1 file changed, 181 insertions(+) create mode 100644 tools/tracing/rtla/Documentation/rtla-timerlat-top.txt diff --git a/tools/tracing/rtla/Documentation/rtla-timerlat-top.txt b/tools/tracing/rtla/Documentation/rtla-timerlat-top.txt new file mode 100644 index 000000000000..59bc8f2ea6cd --- /dev/null +++ b/tools/tracing/rtla/Documentation/rtla-timerlat-top.txt @@ -0,0 +1,181 @@ +rtla-timerlat-top(1) +==================== + +NAME +---- +rtla-timerlat-top - Measures the operating system timer latency + +SYNOPSIS +-------- +*rtla timerlat top* ['OPTIONS'] ... + +DESCRIPTION +The rtla-timerlat-top(1) mode displays a summary of the periodic output +from the timerlat tracer. + +The timerlat tracer dispatches a kernel thread per-cpu. These threads +set a periodic timer to wake themselves up and go back to sleep. After +the wakeup, they collect and generate useful information for the +debugging of operating system timer latency. + +The timerlat tracer outputs information in two ways. It periodically +prints the timer latency at the timer 'IRQ' handler and the 'Thread' handler. +It also provides information for each noise via the osnoise tracepoints +that can be seem with the option -T. + +OPTIONS +------- +*-h*, *--help*:: +Print help menu. +*-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. +*-c*, *--cpus* 'cpu-list':: +Set the timerlat tracer to run the sample threads in the cpu-list. +*-d*, *--duration* 'time[s|m|h|d]':: +Set the duration of the session. +*-T*, *--trace*['=file']:: +Save the stopped trace to ['file|timerlat_trace.txt']. +*-q*, *--quiet*:: +Print only a summary at the end of the session. +*-P*, *--priority* 'o:prio|r:prio|f:prio|d:runtime:period':: +Set scheduling parameters to the timerlat tracer threads, the format to set +the priority are: + - 'o:prio' - use SCHED_OTHER with 'prio'; + - 'r:prio' - use SCHED_RR with 'prio'; + - 'f:prio' - use SCHED_FIFO with 'prio'; + - 'd:runtime[us|ms|s]:period[us|ms|s]' - use SCHED_DEADLINE with 'runtime' +and 'period' in nanoseconds. + +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 *irq_noise* event, was also high +and added more *12553 ns* to the Thread latency. Finally, the *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 timerlat was dispatched without changing timerlat threads' priority. +That is generally not needed because the thread has 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 + +REPORTING BUGS +-------------- +Report bugs to + +LICENSE +------- +rtla is Free Software licensed under the GNU GPLv2 + +COPYING +------- +Copyright \(C) 2021 Red Hat, Inc. Free use of this software is granted under +the terms of the GNU Public License (GPL).