linux-kernel - Re: [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS

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Date:   Tue, 8 Dec 2020 17:03:21 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Peter Ziljstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Linux-ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP

On Tue, 8 Dec 2020 at 16:35, Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> 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@...hsingularity.net>
> ---
>  kernel/sched/fair.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ac7b34e7372b..5c41875aec23 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6153,6 +6153,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>         if (!this_sd)
>                 return -1;

Just noticed while reviewing the patch that the above related to
this_sd can also go under sched_feat(SIS_PROP)

>
> +       cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
> +
>         if (sched_feat(SIS_PROP)) {
>                 u64 avg_cost, avg_idle, span_avg;
>
> @@ -6168,11 +6170,9 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>                         nr = div_u64(span_avg, avg_cost);
>                 else
>                         nr = 4;
> -       }
> -
> -       time = cpu_clock(this);
>
> -       cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
> +               time = cpu_clock(this);
> +       }
>
>         for_each_cpu_wrap(cpu, cpus, target) {
>                 if (!--nr)
> @@ -6181,8 +6181,10 @@ 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;
>  }
> --
> 2.26.2
>