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

Avi Kivity
2011-02-02T10:51:17Z

On 02/02/2011 12:11 PM, Avi Kivity wrote:
> 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.

Of course, it's not enough to just account for this time, you also have
to expose it somewhere, and update tools like top(1) to display it.

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