linux-kernel - Re: [PATCH v2 05/10] sched/fair: reset sched_avg last_update_time before set_task

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Message-ID: <e9a069dd-6215-4725-ca64-7453b6511e35@arm.com>
Date:   Thu, 14 Jul 2022 14:31:58 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Chengming Zhou <zhouchengming@...edance.com>, mingo@...hat.com,
        peterz@...radead.org, vincent.guittot@...aro.org,
        rostedt@...dmis.org, bsegall@...gle.com, vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 05/10] sched/fair: reset sched_avg last_update_time
 before set_task_rq()

On 13/07/2022 06:04, Chengming Zhou wrote:
> set_task_rq() -> set_task_rq_fair() will try to synchronize the blocked
> task's sched_avg when migrate, which is not needed for already detached
> task.
> 
> task_change_group_fair() will detached the task sched_avg from prev cfs_rq
> first, so reset sched_avg last_update_time before set_task_rq() to avoid that.
> 
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>

> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8992ce5e73d2..171bc22bc142 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -11637,12 +11637,12 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
>  static void task_change_group_fair(struct task_struct *p)
>  {
>  	detach_task_cfs_rq(p);
> -	set_task_rq(p, task_cpu(p));
>  
>  #ifdef CONFIG_SMP
>  	/* Tell se's cfs_rq has been changed -- migrated */
>  	p->se.avg.last_update_time = 0;
>  #endif
> +	set_task_rq(p, task_cpu(p));
>  	attach_task_cfs_rq(p);
>  }
>