linux-kernel - Re: [PATCH -next] sched/deadline: Save processing meaningless ops in dl_task_offline

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Date:   Mon, 29 Aug 2022 10:33:50 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Shang XiaoJing <shangxiaojing@...wei.com>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] sched/deadline: Save processing meaningless ops in
 dl_task_offline_migration

On 8/27/22 04:04, Shang XiaoJing wrote:
> Task's bw will be sub from old rd, and add to new rd, even though
> find_lock_later_rq returns a new rq that belong to the same rd with old
> rq. Save ops for moving task's bw if rd is not changed.

This subject is not good. Please change it to a "meaningful" one, describing the
change, not its consequence.

-- Daniel
> Signed-off-by: Shang XiaoJing <shangxiaojing@...wei.com>
> ---
>  kernel/sched/deadline.c | 28 +++++++++++++++-------------
>  1 file changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 3bf4b12ec5b7..58ca9aaa9c44 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -714,20 +714,22 @@ static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p
>  		add_rq_bw(&p->dl, &later_rq->dl);
>  	}
>  
> -	/*
> -	 * And we finally need to fixup root_domain(s) bandwidth accounting,
> -	 * since p is still hanging out in the old (now moved to default) root
> -	 * domain.
> -	 */
> -	dl_b = &rq->rd->dl_bw;
> -	raw_spin_lock(&dl_b->lock);
> -	__dl_sub(dl_b, p->dl.dl_bw, cpumask_weight(rq->rd->span));
> -	raw_spin_unlock(&dl_b->lock);
> +	if (&rq->rd != &later_rq->rd) {
> +		/*
> +		 * And we finally need to fixup root_domain(s) bandwidth accounting,
> +		 * since p is still hanging out in the old (now moved to default) root
> +		 * domain.
> +		 */
> +		dl_b = &rq->rd->dl_bw;
> +		raw_spin_lock(&dl_b->lock);
> +		__dl_sub(dl_b, p->dl.dl_bw, cpumask_weight(rq->rd->span));
> +		raw_spin_unlock(&dl_b->lock);
>  
> -	dl_b = &later_rq->rd->dl_bw;
> -	raw_spin_lock(&dl_b->lock);
> -	__dl_add(dl_b, p->dl.dl_bw, cpumask_weight(later_rq->rd->span));
> -	raw_spin_unlock(&dl_b->lock);
> +		dl_b = &later_rq->rd->dl_bw;
> +		raw_spin_lock(&dl_b->lock);
> +		__dl_add(dl_b, p->dl.dl_bw, cpumask_weight(later_rq->rd->span));
> +		raw_spin_unlock(&dl_b->lock);
> +	}
>  
>  	set_task_cpu(p, later_rq->cpu);
>  	double_unlock_balance(later_rq, rq);