linux-kernel - Re: [PATCH v2 3/6] KVM-GST: KVM Steal time accounting

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Date:	Wed, 02 Feb 2011 12:11:06 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
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>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 3/6] KVM-GST: KVM Steal time accounting

On 02/01/2011 05:57 PM, Glauber Costa wrote:
> On Sun, 2011-01-30 at 16:04 +0200, Avi Kivity wrote:
> >  On 01/28/2011 09:52 PM, Glauber Costa wrote:
> >  >  This patch accounts steal time time in kernel/sched.
> >  >  I kept it from last proposal, because I still see advantages
> >  >  in it: Doing it here will give us easier access from scheduler
> >  >  variables such as the cpu rq. The next patch shows an example of
> >  >  usage for it.
> >  >
> >  >  Since functions like account_idle_time() can be called from
> >  >  multiple places, not only account_process_tick(), steal time
> >  >  grabbing is repeated in each account function separatedely.
> >  >
> >
> >  I accept that steal time is worthwhile, but do you have some way to
> >  demonstrate that the implementation actually works and is beneficial?
> >
> >  Perhaps run two cpu-bound compute processes on one vcpu, overcommit that
> >  vcpu, and see what happens to the processing rate with and without steal
> >  time accounting.  I'd expect a fairer response with steal time accounting.
>
> Avi,
>
> There are two things here:
> One of them, which is solely the accounting of steal time, (patches 1 to
> 4) has absolutely nothing to do with what you said. Its sole purpose is
> to provide the user with information about "why is my process slow if I
> am using 100 % of my cpu?")

Right.  Like irq and softirq time, we need to report this to the user, 
as it's potentially much higher.

> The last patch is the only one that actually tries to rebalance cpus
> according to steal time information. For that, I do have some
> experiments I did here to see if it is working, will try to provide more
> precise data in the next submission.
>

Thanks.

-- 
error compiling committee.c: too many arguments to function

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