linux-kernel - Re: [PATCH 1/4] sched/fair: Only set slice protection at pick time

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Message-ID: <CAKfTPtA4b0pJrevJT=hFjn45iB=yms+vXwX9LKv4rrH6syLs_w@mail.gmail.com>
Date: Fri, 30 Jan 2026 16:52:25 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, juri.lelli@...hat.com, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, 
	linux-kernel@...r.kernel.org, wangtao554@...wei.com, quzicheng@...wei.com, 
	kprateek.nayak@....com, wuyun.abel@...edance.com, dsmythies@...us.net
Subject: Re: [PATCH 1/4] sched/fair: Only set slice protection at pick time

On Fri, 30 Jan 2026 at 10:47, Peter Zijlstra <peterz@...radead.org> wrote:
>
> We should not (re)set slice protection in the sched_change pattern
> which calls put_prev_task() / set_next_task().
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

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

> ---
>  kernel/sched/fair.c |   11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5420,7 +5420,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
>  }
>
>  static void
> -set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
> +set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, bool first)
>  {
>         clear_buddies(cfs_rq, se);
>
> @@ -5435,7 +5435,8 @@ set_next_entity(struct cfs_rq *cfs_rq, s
>                 __dequeue_entity(cfs_rq, se);
>                 update_load_avg(cfs_rq, se, UPDATE_TG);
>
> -               set_protect_slice(cfs_rq, se);
> +               if (first)
> +                       set_protect_slice(cfs_rq, se);
>         }
>
>         update_stats_curr_start(cfs_rq, se);
> @@ -8958,13 +8959,13 @@ pick_next_task_fair(struct rq *rq, struc
>                                 pse = parent_entity(pse);
>                         }
>                         if (se_depth >= pse_depth) {
> -                               set_next_entity(cfs_rq_of(se), se);
> +                               set_next_entity(cfs_rq_of(se), se, true);
>                                 se = parent_entity(se);
>                         }
>                 }
>
>                 put_prev_entity(cfs_rq, pse);
> -               set_next_entity(cfs_rq, se);
> +               set_next_entity(cfs_rq, se, true);
>
>                 __set_next_task_fair(rq, p, true);
>         }
> @@ -13578,7 +13579,7 @@ static void set_next_task_fair(struct rq
>         for_each_sched_entity(se) {
>                 struct cfs_rq *cfs_rq = cfs_rq_of(se);
>
> -               set_next_entity(cfs_rq, se);
> +               set_next_entity(cfs_rq, se, first);
>                 /* ensure bandwidth has been allocated on our new cfs_rq */
>                 account_cfs_rq_runtime(cfs_rq, 0);
>         }
>
>