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

Avi Kivity
2011-02-02T10:11:06Z

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.

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