linux-kernel - Re: [PATCH] sched/deadline: Remove redundant code replenishing runtime

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Message-ID: <20170210133933.GA6123@e106622-lin>
Date:   Fri, 10 Feb 2017 13:39:33 +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, tkhai@...dex.ru
Subject: Re: [PATCH] sched/deadline: Remove redundant code replenishing
 runtime

Hi,

On 10/02/17 18:11, Byungchul Park wrote:
> For a task passing its deadline while !rq, it will be replenished
> in the following path because dl_se->deadline < rq_lock.
> 
>    enqueue_dl_entity(ENQUEUE_WAKEUP)
>       update_dl_entity
> 
> Therefore, code replenishing it in the timer callback in the case is
> unnecessary. This is not for enhancing performance but just for removing
> a redundant code.
> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>  kernel/sched/deadline.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 27737f3..9c77696 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -624,10 +624,8 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
>  	 * We can be both throttled and !queued. Replenish the counter
>  	 * but do not enqueue -- wait for our wakeup to do that.
>  	 */
> -	if (!task_on_rq_queued(p)) {
> -		replenish_dl_entity(dl_se, dl_se);

I think we actually want to replenish and set the next deadline at this
point of time, not the one that we get when the task will eventually wake up.

Best,

- Juri