linux-kernel - Re: [PATCH 16/16] KVM-GST: adjust scheduler cpu power

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Date:	Wed, 26 Jan 2011 16:11:56 -0200
From:	Glauber Costa <glommer@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com, Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH 16/16] KVM-GST: adjust scheduler cpu power

On Wed, 2011-01-26 at 17:46 +0100, Peter Zijlstra wrote:
> On Wed, 2011-01-26 at 13:43 -0200, Glauber Costa wrote:
> 
> > yes, but once this delta is subtracted from rq->clock_task, this value is not
> > used to dictate power, unless I am mistaken.
> > 
> > power is adjusted according to scale_rt_power(), which does it using the
> > values of rq->rt_avg, rq->age_stamp, and rq->clock.
> > 
> > So whatever I store into rq->clock_task, but not rq->clock (which
> > correct me if I'm wrong, is expected to be walltime), will not be used
> > to adjust cpu power, which is what I'm trying to achieve.
> 
> No, see the below, it uses a per-cpu virt_steal_time() clock which is
> expected to return steal-time in ns.
> 
> All time not accounted to ->clock_task is accumulated in lost, and
> passed into sched_rt_avg_update() and thus affects the cpu_power.
> 
> If it finds that 50% of the (recent) time is steal time, its cpu_power
> will be 50%.
ok, now I get your proposal. It does make sense.

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