linux-kernel - Re: [PATCH v6 8/9] sched/fair: move task sched_avg attach to enqueue_task

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Date:   Tue, 23 Aug 2022 09:48:56 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     dietmar.eggemann@....com, mingo@...hat.com, peterz@...radead.org,
        rostedt@...dmis.org, bsegall@...gle.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, tj@...nel.org
Subject: Re: [PATCH v6 8/9] sched/fair: move task sched_avg attach to enqueue_task_fair()

On Thu, 18 Aug 2022 at 14:48, Chengming Zhou
<zhouchengming@...edance.com> wrote:
>
> When wake_up_new_task(), we use post_init_entity_util_avg() to init
> util_avg/runnable_avg based on cpu's util_avg at that time, and
> attach task sched_avg to cfs_rq.
>
> Since enqueue_task_fair() -> enqueue_entity() -> update_load_avg()
> loop will do attach, we can move this work to update_load_avg().
>
> wake_up_new_task(p)
>   post_init_entity_util_avg(p)
>     attach_entity_cfs_rq()  --> (1)
>   activate_task(rq, p)
>     enqueue_task() := enqueue_task_fair()
>       enqueue_entity() loop
>         update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH)
>           if (!se->avg.last_update_time && (flags & DO_ATTACH))
>             attach_entity_load_avg()  --> (2)
>
> This patch move attach from (1) to (2), update related comments too.
>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

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

> ---
>  kernel/sched/fair.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c319b0bd2bc1..93d7c7b110dd 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -799,8 +799,6 @@ void init_entity_runnable_average(struct sched_entity *se)
>         /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
>  }
>
> -static void attach_entity_cfs_rq(struct sched_entity *se);
> -
>  /*
>   * With new tasks being created, their initial util_avgs are extrapolated
>   * based on the cfs_rq's current util_avg:
> @@ -863,8 +861,6 @@ void post_init_entity_util_avg(struct task_struct *p)
>                 se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
>                 return;
>         }
> -
> -       attach_entity_cfs_rq(se);
>  }
>
>  #else /* !CONFIG_SMP */
> @@ -4002,8 +3998,7 @@ static void migrate_se_pelt_lag(struct sched_entity *se) {}
>   * @cfs_rq: cfs_rq to update
>   *
>   * The cfs_rq avg is the direct sum of all its entities (blocked and runnable)
> - * avg. The immediate corollary is that all (fair) tasks must be attached, see
> - * post_init_entity_util_avg().
> + * avg. The immediate corollary is that all (fair) tasks must be attached.
>   *
>   * cfs_rq->avg is used for task_h_load() and update_cfs_share() for example.
>   *
> @@ -4236,8 +4231,8 @@ static void remove_entity_load_avg(struct sched_entity *se)
>
>         /*
>          * tasks cannot exit without having gone through wake_up_new_task() ->
> -        * post_init_entity_util_avg() which will have added things to the
> -        * cfs_rq, so we can remove unconditionally.
> +        * enqueue_task_fair() which will have added things to the cfs_rq,
> +        * so we can remove unconditionally.
>          */
>
>         sync_entity_load_avg(se);
> --
> 2.37.2
>