linux-kernel - Re: [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence of idle CPUs

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Date:   Mon, 9 Dec 2019 11:50:12 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Todd Kjos <tkjos@...gle.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        quentin.perret@...aro.org, chris.redpath@....com,
        steven.sistare@...cle.com, subhra.mazumdar@...cle.com,
        songliubraving@...com
Subject: Re: [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence
 of idle CPUs

On Wed, 26 Jun 2019 at 13:07, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> Hi,
>
> We try to find an idle CPU to run the next task, but in case we don't
> find an idle CPU it is better to pick a CPU which will run the task the
> soonest, for performance reason.
>
> A CPU which isn't idle but has only SCHED_IDLE activity queued on it
> should be a good target based on this criteria as any normal fair task
> will most likely preempt the currently running SCHED_IDLE task
> immediately. In fact, choosing a SCHED_IDLE CPU over a fully idle one
> shall give better results as it should be able to run the task sooner
> than an idle CPU (which requires to be woken up from an idle state).
>
> This patchset updates both fast and slow paths with this optimization.
>
> Testing is done with the help of rt-app currently and here are the
> details:
>
> - Tested on Octacore Hikey platform (all CPUs change frequency
>   together).
>
> - rt-app json [1] creates few tasks and we monitor the scheduling
>   latency for them by looking at "wu_lat" field (usec).
>
> - The histograms are created using
>   https://github.com/adkein/textogram: textogram -a 0 -z 1000 -n 10
>
> - the stats are accumulated using: https://github.com/nferraz/st

Hi Viresh,

Thanks for the great work! Could you give the whole commad-line for us testing?

    Wanpeng