linux-kernel - Re: [PATCH] sched/core: An optimization of pick_next

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Message-ID: <CABk29Nt=a0RPfoVMP=FiKY_ObtU9enYU3cK00RgDUVqJrTmkiQ@mail.gmail.com>
Date:   Mon, 16 Aug 2021 12:02:34 -0700
From:   Josh Don <joshdon@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tao Zhou <tao.zhou@...ux.dev>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        "Hyser,Chris" <chris.hyser@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH] sched/core: An optimization of pick_next_task() not sure

On Mon, Aug 16, 2021 at 11:53 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Aug 16, 2021 at 11:44:01PM +0800, Tao Zhou wrote:
> > When find a new candidate max, wipe the stale and start over.
> > Goto again: and use the new max to loop to pick the the task.
> >
> > Here first want to get the max of the core and use this new
> > max to loop once to pick the task on each thread.
> >
> > Not sure this is an optimization and just stop here a little
> > and move on..
> >
>
> Did you find this retry was an issue on your workload? Or was this from
> reading the source?

I would be surprised if this made a noticeable difference on SMT2, but
I could certainly see how this would help with larger SMT
configurations where we have more opportunities to invalidate the
other siblings.