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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Tue, 8 Dec 2020 14:43:10 +0100
Message-ID: <CAKfTPtDbUoVSvnjFrpomvTJD0jCA6vH_Y3LP=csW8fHntOG_6A@mail.gmail.com>
Subject: Re: [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     Dietmar Eggemann <dietmar.eggemann@arm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Barry Song <song.bao.hua@hisilicon.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Ziljstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Linux-ARM <linux-arm-kernel@lists.infradead.org>
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On Tue, 8 Dec 2020 at 14:36, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Tue, Dec 08, 2020 at 02:24:32PM +0100, Vincent Guittot wrote:
> > > > Nitpick:
> > > >
> > > > Since now avg_cost and avg_idle are only used w/ SIS_PROP, they could go
> > > > completely into the SIS_PROP if condition.
> > > >
> > >
> > > Yeah, I can do that. In the initial prototype, that happened in a
> > > separate patch that split out SIS_PROP into a helper function and I
> > > never merged it back. It's a trivial change.
> >
> > while doing this, should you also put the update of
> > this_sd->avg_scan_cost under the SIS_PROP feature ?
> >
>
> It's outside the scope of the series but why not. This?
>
> --8<--
> sched/fair: Move avg_scan_cost calculations under SIS_PROP
>
> As noted by Vincent Guittot, avg_scan_costs are calculated for SIS_PROP
> even if SIS_PROP is disabled. Move the time calculations under a SIS_PROP
> check and while we are at it, exclude the cost of initialising the CPU
> mask from the average scan cost.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 19ca0265f8aa..0fee53b1aae4 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6176,10 +6176,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>                         nr = 4;
>         }
>
> -       time = cpu_clock(this);

I would move it in the if (sched_feat(SIS_PROP)) above.

> -
>         cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>
> +       if (sched_feat(SIS_PROP))
> +               time = cpu_clock(this);
>         for_each_cpu_wrap(cpu, cpus, target) {
>                 if (!--nr)
>                         return -1;
> @@ -6187,8 +6187,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>                         break;
>         }
>
> -       time = cpu_clock(this) - time;
> -       update_avg(&this_sd->avg_scan_cost, time);
> +       if (sched_feat(SIS_PROP)) {
> +               time = cpu_clock(this) - time;
> +               update_avg(&this_sd->avg_scan_cost, time);
> +       }
>
>         return cpu;
>  }