linux-kernel - Re: [RFC][PATCH 2/4] sched: Push put_prev_task() into pick_next

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Message-ID: <4FE2CEB0.7080200@linux.vnet.ibm.com>
Date:	Thu, 21 Jun 2012 15:35:12 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	mingo@...nel.org, pjt@...gle.com, venki@...gle.com, efault@....de,
	rostedt@...dmis.org, glommer@...allels.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 2/4] sched: Push put_prev_task() into pick_next_task()


> +pick_next_task_fair(struct rq *rq, struct task_struct *prev)
>  {
>  	struct task_struct *p;
>  	struct cfs_rq *cfs_rq = &rq->cfs;
> @@ -2999,6 +3000,9 @@ static struct task_struct *pick_next_tas
>  	if (!cfs_rq->nr_running)
>  		return NULL;
> 
> +	if (prev)
> +		prev->sched_class->put_prev_task(rq, prev);
> +
>  	do {
>  		se = pick_next_entity(cfs_rq);
>  		set_next_entity(cfs_rq, se);
> --- a/kernel/sched/idle_task.c
> +++ b/kernel/sched/idle_task.c
> @@ -22,8 +22,12 @@ static void check_preempt_curr_idle(stru
>  	resched_task(rq->idle);
>  }

Will it cause trouble when the last task on cfs_rq was dequeued before
been putted?

The cfs_rq->nr_running will be 0 and we will miss the chance to put
prev, will we?

Regards,
Michael Wang

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