linux-kernel - Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity

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Date:	Fri, 29 Jul 2011 14:21:58 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, mingo@...e.hu,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick

On Thu, Jul 28, 2011 at 05:43:23PM +0800, Lin Ming wrote:
> Currently, entity_tick calls check_preempt_tick if WAKEUP_PREEMPT feature is
> disabled. That's wrong. It should do that if the feature is enabled.

Why is it wrong?
check_preempt_wakeup() is used for wakeup.

> 
> And actually the check is duplicate because check_preempt_tick will do
> that. So just remove it from entity_tick.

It's not exactly duplicated. entity_tick() will resched_task(*p)
if p's slice is over. So if there is an following wakeup(say X),
then there is an opportunity for X to schedule quickly.

Thanks,
Yong

> 
> Signed-off-by: Lin Ming <ming.m.lin@...el.com>
> ---
>  kernel/sched_fair.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index bc8ee99..af2fe9d 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -1233,7 +1233,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
>  		return;
>  #endif
>  
> -	if (cfs_rq->nr_running > 1 || !sched_feat(WAKEUP_PREEMPT))
> +	if (cfs_rq->nr_running > 1)
>  		check_preempt_tick(cfs_rq, curr);
>  }
>  
> -- 
> 1.7.2.3
> 
> 
> 
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