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Date: Wed, 25 Feb 2009 12:13:55 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: miaox@cn.fujitsu.com, Linux-Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched: fix unfairness when upgrade weight
Message-ID: <20090225111355.GD15453@elte.hu>
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* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> > --- a/kernel/sched_fair.c
> > +++ b/kernel/sched_fair.c
> > @@ -1690,6 +1690,15 @@ static void task_new_fair(struct rq *rq, struct task_struct *p)
> >  static void prio_changed_fair(struct rq *rq, struct task_struct *p,
> >  			      int oldprio, int running)
> >  {
> > +	struct cfs_rq *cfs_rq = task_cfs_rq(p);
> > +	struct sched_entity *se = &p->se;
> > +	int on_rq = se->on_rq;
> > +
> > +	if (p->prio < oldprio && on_rq) {
> > +		dequeue_entity(cfs_rq, se, 0);
> > +		se->vruntime = cfs_rq->min_vruntime + sched_vslice(cfs_rq, se);
> > +		enqueue_entity(cfs_rq, se, 0);
> > +	}
> 
> we very likely just enqueued the thing, and now we dequeue/enqueue
> again.. not very nice.

but priority-change is a slowpath, so it shouldnt matter much, 
should it?

	Ingo