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

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Date:   Wed, 4 Sep 2019 14:21:48 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        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
Subject: Re: [PATCH 2/2] sched/debug: add sched_update_nr_running tracepoint

On 04/09/2019 14:13, Peter Zijlstra wrote:
> On Tue, Sep 03, 2019 at 05:43:40PM +0200, Radim Krčmář wrote:
> 
>> 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.
> 
> You should be able to reconstruct this from wakeup and switch
> tracepoints.
> 
> 

I never tried to do it myself but know some folks around me gave it a go
(Morten, Qais and maybe even Chris). I can't remember the exact details but
there was something about not getting the right input - duplicated wakeups,
or no migration information (I think sched_migrate doesn't cover all of the
cases) so the information you're building diverges as time progresses.