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

Glauber Costa
2011-02-01T15:57:10Z

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?")

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.