linux-kernel - Re: [PATCH] sched/deadline: Remove unnecessary condition in push_dl

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Date:   Wed, 15 Feb 2017 10:47:49 +0000
From:   Juri Lelli <juri.lelli@....com>
To:     Byungchul Park <byungchul.park@....com>
Cc:     peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, juri.lelli@...il.com,
        kernel-team@....com, Steven Rostedt <rostedt@...dmis.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>
Subject: Re: [PATCH] sched/deadline: Remove unnecessary condition in
 push_dl_task()

[+Steve, Luca]

Hi,

On 15/02/17 14:11, Byungchul Park wrote:
> Once pick_next_pushable_dl_task(rq) return a task, it guarantees that
> the task's cpu is rq->cpu, so task_cpu(next_task) is always rq->cpu if
> task == next_task. Remove a redundant condition and make code simpler.
> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>  kernel/sched/deadline.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 27737f3..ad8d577 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1483,7 +1483,7 @@ static int push_dl_task(struct rq *rq)
>  		 * then possible that next_task has migrated.
>  		 */
>  		task = pick_next_pushable_dl_task(rq);
> -		if (task_cpu(next_task) == rq->cpu && task == next_task) {
> +		if (task == next_task) {

Seems a sensible optimization to me. Actually, we are doing the same for
rt.c; Steve, Peter, do you think we should optimize that as well?

Thanks,

- Juri