linux-kernel - Re: [PATCH] sched/fair: Make sched-idle cpu selection consistent throughout

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Message-ID: <CAKohpo=hssu_uvb1J=0Od=KziAQVSMmbBt9zxa4mYttKhFJwFw@mail.gmail.com>
Date:   Thu, 31 Oct 2019 14:42:03 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: Make sched-idle cpu selection consistent throughout

On Wed, 30 Oct 2019 at 22:17, Mel Gorman <mgorman@...e.de> wrote:

> As the patch stands, I think a fork-intensive workload where each
> process is doing small amounts of work will suffer from overloading
> domains and have variable performance depending on how quickly the load
> balancer reacts.

Just wanted to clarify this slightly in case it is confusing. Once a
newly forked
(non SCHED_IDLE) task gets placed on a sched-idle CPU, it won't remain
sched-idle anymore and we will again start looking for a fully idle CPU. So,
we won't put everything on a small set of CPUs, but just one SCHED_NORMAL
task on a CPU unless we are out of idle CPUs.

Do you have some specific test in mind which I can run to test this ?

--
Viresh