linux-kernel - Re: [PATCH 2/2] sched/debug: add sched_update_nr

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Date:   Wed, 4 Sep 2019 14:55:21 +0800
From:   "chengjian (D)" <cj.chengjian@...wei.com>
To:     Valentin Schneider <valentin.schneider@....com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        <linux-kernel@...r.kernel.org>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jirka Hladký <jhladky@...hat.com>,
        Jiří Vozár <jvozar@...hat.com>,
        <x86@...nel.org>, "Qais Yousef" <qais.yousef@....com>,
        "chengjian (D)" <cj.chengjian@...wei.com>,
        "Xiexiuqi (Xie XiuQi)" <xiexiuqi@...wei.com>,
        Li Bin <huawei.libin@...wei.com>, <bobo.shaobowang@...wei.com>
Subject: Re: [PATCH 2/2] sched/debug: add sched_update_nr_running tracepoint


On 2019/9/4 0:05, Valentin Schneider wrote:
> On 03/09/2019 16:43, Radim Krčmář wrote:
>> The paper "The Linux Scheduler: a Decade of Wasted Cores" used several
>> custom data gathering points to better understand what was going on in
>> the scheduler.
>> Red Hat adapted one of them for the tracepoint framework and created a
>> tool to plot a heatmap of nr_running, where the sched_update_nr_running
>> tracepoint is being used for fine grained monitoring of scheduling
>> imbalance.
>> The tool is available from https://github.com/jirvoz/plot-nr-running.
>>
>> The best place for the tracepoints is inside the add/sub_nr_running,
>> which requires some shenanigans to make it work as they are defined
>> inside sched.h.
>> The tracepoints have to be included from sched.h, which means that
>> CREATE_TRACE_POINTS has to be defined for the whole header and this
>> might cause problems if tree-wide headers expose tracepoints in sched.h
>> dependencies, but I'd argue it's the other side's misuse of tracepoints.
>>
>> Moving the import sched.h line lower would require fixes in s390 and ppc
>> headers, because they don't include dependecies properly and expect
>> sched.h to do it, so it is simpler to keep sched.h there and
>> preventively undefine CREATE_TRACE_POINTS right after.
>>
>> Exports of the pelt tracepoints remain because they don't need to be
>> protected by CREATE_TRACE_POINTS and moving them closer would be
>> unsightly.
>>
> Pure trace events are frowned upon in scheduler world, try going with
> trace points. Qais did something very similar recently:
>
> https://lore.kernel.org/lkml/20190604111459.2862-1-qais.yousef@arm.com/
>
> You'll have to implement the associated trace events in a module, which
> lets you define your own event format and doesn't form an ABI :).
>
> .


Hi Radim,


Why not try Chrome Tracing

1--Record trace data, scheduling, irq, etc.
     You can Produce a JSON file with the format expected by Chrome
     OR
     just save the captured data directly as "xxx.html", it can still work.
     cat /sys/kernel/debug/tracing/trace > trace.html
2--Go to chrome://tracing in Chrome,
3--Click "Load" and open your file, or alternatively drag the file into 
Chrome,
4--Profit!


Systrace (Android System Trace) captures and displays execution times of 
your app's
processes and other Android system processes, fortunately, there are 
some ported
versions for Linux Desktop/Server.

https://github.com/gatieme/systrace



references--
https://www.chromium.org/developers/how-tos/trace-event-profiling-tool
https://www.chromium.org/developers/how-tos/trace-event-profiling-tool/trace-event-reading


Thanks,
     - Cheng Jian.