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    SubjectRe: [PATCH v2 3/6] KVM-GST: KVM Steal time accounting
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    On Wed, 2011-02-02 at 12:51 +0200, Avi Kivity wrote:
    > 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.
    Yes, what I meant is that just the accounting will just expose it to the
    tools, won't affect the scheduler in any sense.




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