linux-kernel - Re: [PATCH v3 2/4] sched: account number of SCHED_IDLE entities on each cfs

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Date:   Tue, 24 Aug 2021 09:57:47 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Paul Turner <pjt@...gle.com>,
        Oleg Rombakh <olegrom@...gle.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Steve Sistare <steven.sistare@...cle.com>,
        Tejun Heo <tj@...nel.org>, Rik van Riel <riel@...riel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] sched: account number of SCHED_IDLE entities on
 each cfs_rq

On Fri, 20 Aug 2021 at 03:04, Josh Don <joshdon@...gle.com> wrote:
>
> Adds cfs_rq->idle_nr_running, which accounts the number of idle entities
> directly enqueued on the cfs_rq.
>
> Signed-off-by: Josh Don <joshdon@...gle.com>

Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

> ---
>  kernel/sched/debug.c |  2 ++
>  kernel/sched/fair.c  | 25 ++++++++++++++++++++++++-
>  kernel/sched/sched.h |  1 +
>  3 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 49716228efb4..33538579db9a 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -608,6 +608,8 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
>                         cfs_rq->nr_spread_over);
>         SEQ_printf(m, "  .%-30s: %d\n", "nr_running", cfs_rq->nr_running);
>         SEQ_printf(m, "  .%-30s: %d\n", "h_nr_running", cfs_rq->h_nr_running);
> +       SEQ_printf(m, "  .%-30s: %d\n", "idle_nr_running",
> +                       cfs_rq->idle_nr_running);
>         SEQ_printf(m, "  .%-30s: %d\n", "idle_h_nr_running",
>                         cfs_rq->idle_h_nr_running);
>         SEQ_printf(m, "  .%-30s: %ld\n", "load", cfs_rq->load.weight);
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5aa3cfd15a2e..19a9244c140f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2995,6 +2995,8 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>         }
>  #endif
>         cfs_rq->nr_running++;
> +       if (se_is_idle(se))
> +               cfs_rq->idle_nr_running++;
>  }
>
>  static void
> @@ -3008,6 +3010,8 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>         }
>  #endif
>         cfs_rq->nr_running--;
> +       if (se_is_idle(se))
> +               cfs_rq->idle_nr_running--;
>  }
>
>  /*
> @@ -5573,6 +5577,17 @@ static int sched_idle_rq(struct rq *rq)
>                         rq->nr_running);
>  }
>
> +/*
> + * Returns true if cfs_rq only has SCHED_IDLE entities enqueued. Note the use
> + * of idle_nr_running, which does not consider idle descendants of normal
> + * entities.
> + */
> +static bool sched_idle_cfs_rq(struct cfs_rq *cfs_rq)
> +{
> +       return cfs_rq->nr_running &&
> +               cfs_rq->nr_running == cfs_rq->idle_nr_running;
> +}
> +
>  #ifdef CONFIG_SMP
>  static int sched_idle_cpu(int cpu)
>  {
> @@ -11556,7 +11571,7 @@ int sched_group_set_idle(struct task_group *tg, long idle)
>         for_each_possible_cpu(i) {
>                 struct rq *rq = cpu_rq(i);
>                 struct sched_entity *se = tg->se[i];
> -               struct cfs_rq *grp_cfs_rq = tg->cfs_rq[i];
> +               struct cfs_rq *parent_cfs_rq, *grp_cfs_rq = tg->cfs_rq[i];
>                 bool was_idle = cfs_rq_is_idle(grp_cfs_rq);
>                 long idle_task_delta;
>                 struct rq_flags rf;
> @@ -11567,6 +11582,14 @@ int sched_group_set_idle(struct task_group *tg, long idle)
>                 if (WARN_ON_ONCE(was_idle == cfs_rq_is_idle(grp_cfs_rq)))
>                         goto next_cpu;
>
> +               if (se->on_rq) {
> +                       parent_cfs_rq = cfs_rq_of(se);
> +                       if (cfs_rq_is_idle(grp_cfs_rq))
> +                               parent_cfs_rq->idle_nr_running++;
> +                       else
> +                               parent_cfs_rq->idle_nr_running--;
> +               }
> +
>                 idle_task_delta = grp_cfs_rq->h_nr_running -
>                                   grp_cfs_rq->idle_h_nr_running;
>                 if (!cfs_rq_is_idle(grp_cfs_rq))
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 8dfad8fb756c..6af039e433fb 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -530,6 +530,7 @@ struct cfs_rq {
>         struct load_weight      load;
>         unsigned int            nr_running;
>         unsigned int            h_nr_running;      /* SCHED_{NORMAL,BATCH,IDLE} */
> +       unsigned int            idle_nr_running;   /* SCHED_IDLE */
>         unsigned int            idle_h_nr_running; /* SCHED_IDLE */
>
>         u64                     exec_clock;
> --
> 2.33.0.rc2.250.ged5fa647cd-goog
>