linux-kernel - Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr

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Date:   Thu, 23 Sep 2021 14:41:06 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Mike Galbraith <efault@....de>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to nr_running

On Thu, 23 Sept 2021 at 11:22, Mike Galbraith <efault@....de> wrote:
>
> On Thu, 2021-09-23 at 10:40 +0200, Vincent Guittot wrote:
> >
> > a 100us value should even be enough to fix Mel's problem without
> > impacting common wakeup preemption cases.
>
> It'd be nice if it turn out to be something that simple, but color me
> skeptical.  I've tried various preemption throttling schemes, and while

Let's see what the results will show. I tend to agree that this will
not be enough to cover all use cases and I don't see any other way to
cover all cases than getting some inputs from the threads about their
latency fairness which bring us back to some kind of latency niceness
value

> it was trivial to get promising results, my scheme always managed to
> harm something.  Everything I ever tried, I ended up tossing.
>
>         -Mike