linux-kernel - Re: [RESEND PATCH v3] sched/deadline: Remove unnecessary condition in push_dl

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Date:   Thu, 18 May 2017 11:00:04 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@....com,
        rostedt@...dmis.org, juri.lelli@....com, bristot@...hat.com
Subject: Re: [RESEND PATCH v3] sched/deadline: Remove unnecessary condition
 in push_dl_task()

On Fri, May 12, 2017 at 10:05:59AM +0900, Byungchul Park wrote:
> pick_next_pushable_dl_task(rq) has BUG_ON(rq->cpu != task_cpu(task))
> when it returns a task other than NULL, which means that task_cpu(task)
> must be rq->cpu. So if task == next_task, then task_cpu(next_task) must
> be rq->cpu as well. Remove the redundant condition and make code simpler.
> 
> By this patch, unnecessary one branch and two LOAD operations in 'if'
> statement can be avoided.

+cc rostedt@...dmis.org
+cc juri.lelli@....com
+cc bristot@...hat.com

> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> Reviewed-by: Juri Lelli <juri.lelli@....com>
> Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.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) {
>  			/*
>  			 * The task is still there. We don't try
>  			 * again, some other cpu will pull it when ready.
> -- 
> 1.9.1