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

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Date:	Tue, 25 Jan 2011 18:02:36 -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 Mon, 2011-01-24 at 20:51 +0100, Peter Zijlstra wrote:
> On Mon, 2011-01-24 at 16:51 -0200, Glauber Costa wrote:
> > > I would really much rather see you change update_rq_clock_task() and
> > > subtract your ns resolution steal time from our wall-time,
> > > update_rq_clock_task() already updates the cpu_power relative to the
> > > remaining time available.
> > 
> > But then we get into the problems we already discussed in previous
> > submissions, which is, we don't really want to alter any notion of
> > wallclock time. Could you list any more concrete advantages of the
> > specific way you proposed? 
> 
> clock_task is the time spend on the task, by not taking steal time into
> account all steal time is accounted as service to whatever task was
> current when the vcpu wasn't running.
> 
> It doesn't change wall-time in the sense of gtod, only the service time
> to tasks.
I fail to see how does clock_task influence cpu power.
If we also have to touch clock_task for better accounting of other
stuff, it is a separate story.
But for cpu_power, I really fail. Please enlighten me.

I did have slightly better results accounting the whole steal time
period away from total_"ticks"(*) than just with units.

* Please note again that ticks here is just a (bad, I admit) name.
This is not tick accounting, is just an estimate of how much useful work
your cpu did.


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