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References: <20230406155030.1989554-1-dietmar.eggemann@arm.com> <20230406155030.1989554-2-dietmar.eggemann@arm.com>
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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Wed, 3 May 2023 18:08:54 +0200
Message-ID: <CAKfTPtDh_aQn15to7E9JypVXarFVcEL+jiWJMV6J7-Gijj9SyQ@mail.gmail.com>
Subject: Re: [PATCH 1/1] sched: Consider CPU contention in frequency &
 load-balance busiest CPU selection
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Qais Yousef <qyousef@layalina.io>,
        Kajetan Puchalski <kajetan.puchalski@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Vincent Donnefort <vdonnefort@google.com>,
        Quentin Perret <qperret@google.com>,
        Abhijeet Dharmapurikar <adharmap@quicinc.com>,
        linux-kernel@vger.kernel.org
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On Thu, 6 Apr 2023 at 17:50, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>
> Use new cpu_boosted_util_cfs() instead of cpu_util_cfs().
>
> The former returns max(util_avg, runnable_avg) capped by max CPU
> capacity. CPU contention is thereby considered through runnable_avg.
>
> The change in load-balance only affects migration type `migrate_util`.

would be good to get some figures to show the benefit

>
> Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> ---
>  kernel/sched/cpufreq_schedutil.c |  3 ++-
>  kernel/sched/fair.c              |  2 +-
>  kernel/sched/sched.h             | 19 +++++++++++++++++++
>  3 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index e3211455b203..728b186cd367 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -158,7 +158,8 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu)
>         struct rq *rq = cpu_rq(sg_cpu->cpu);
>
>         sg_cpu->bw_dl = cpu_bw_dl(rq);
> -       sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu),
> +       sg_cpu->util = effective_cpu_util(sg_cpu->cpu,
> +                                         cpu_boosted_util_cfs(sg_cpu->cpu),

Shouldn't we have a similar change in feec to estimate correctly which
OPP/ freq will be selected by schedutil ?


>                                           FREQUENCY_UTIL, NULL);
>  }
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bc358dc4faeb..5ae36224a1c2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10481,7 +10481,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
>                         break;
>
>                 case migrate_util:
> -                       util = cpu_util_cfs(i);
> +                       util = cpu_boosted_util_cfs(i);
>
>                         /*
>                          * Don't try to pull utilization from a CPU with one
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 060616944d7a..f42c859579d9 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2994,6 +2994,25 @@ static inline unsigned long cpu_util_cfs(int cpu)
>         return min(util, capacity_orig_of(cpu));
>  }
>
> +/*
> + * cpu_boosted_util_cfs() - Estimates the amount of CPU capacity used by
> + *                          CFS tasks.
> + *
> + * Similar to cpu_util_cfs() but also take possible CPU contention into
> + * consideration.
> + */
> +static inline unsigned long cpu_boosted_util_cfs(int cpu)
> +{
> +       unsigned long runnable;
> +       struct cfs_rq *cfs_rq;
> +
> +       cfs_rq = &cpu_rq(cpu)->cfs;
> +       runnable = READ_ONCE(cfs_rq->avg.runnable_avg);
> +       runnable = min(runnable, capacity_orig_of(cpu));
> +
> +       return max(cpu_util_cfs(cpu), runnable);
> +}
> +
>  static inline unsigned long cpu_util_rt(struct rq *rq)
>  {
>         return READ_ONCE(rq->avg_rt.util_avg);
> --
> 2.25.1
>