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

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Date:	Thu, 21 Jun 2012 10:41:44 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
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()

On Thu, 2012-06-21 at 15:35 +0800, Michael Wang wrote:
> > +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?

pick_next_task_idle() will then do the put, no?
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