linux-kernel - Re: [CFS Bandwidth Control v4 4/7] sched: unthrottle cfs_rq(s) who ran out of quota at period refresh

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Date:	Thu, 24 Feb 2011 12:34:05 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Avi Kivity <avi@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Nikhil Rao <ncrao@...gle.com>
Subject: Re: [CFS Bandwidth Control v4 4/7] sched: unthrottle cfs_rq(s) who
 ran out of quota at period refresh

On Wed, Feb 23, 2011 at 02:32:12PM +0100, Peter Zijlstra wrote:
> On Tue, 2011-02-15 at 19:18 -0800, Paul Turner wrote:
> 
> > +static void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
> > +{
> > +	struct rq *rq = rq_of(cfs_rq);
> > +	struct sched_entity *se;
> > +
> > +	se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
> > +
> > +	update_rq_clock(rq);
> > +	/* (Try to) avoid maintaining share statistics for idle time */
> > +	cfs_rq->load_stamp = cfs_rq->load_last = rq->clock_task;
> 
> Ok, so here you try to compensate for some of the weirdness from the
> previous patch.. wouldn't it be much saner to fully consider the
> throttled things dequeued for the load calculation etc.?
> 
> > +
> > +	cfs_rq->throttled = 0;
> > +	for_each_sched_entity(se) {
> > +		if (se->on_rq)
> > +			break;
> > +
> > +		cfs_rq = cfs_rq_of(se);
> > +		enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
> > +		if (cfs_rq_throttled(cfs_rq))
> > +			break;
> 
> That's just weird, it was throttled, you enqueued it but find it
> throttled.

se got enqueued to cfs_rq, but we find that cfs_rq is throttled and hence
refrain from enqueueing cfs_rq futher.

So essentially enqueing to a throttled cfs_rq is allowed, but a throttled 
group entitiy can't be enqueued further.

Regards,
Bharata.
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