Re: [PATCH v4 0/8] KVM paravirt remote flush tlb

Nikunj A Dadhania
2012-09-04T08:08:50Z

On Tue, 04 Sep 2012 10:51:06 +0300, Avi Kivity <avi@redhat.com> wrote:
> On 09/04/2012 04:30 AM, Nikunj A Dadhania wrote:
> > On Mon, 03 Sep 2012 17:33:46 +0300, Avi Kivity <avi@redhat.com> wrote:
> >> On 08/21/2012 02:25 PM, Nikunj A. Dadhania wrote:
> >> >
> >> > kernbench(lower is better)
> >> > ==========================
> >> > base pvflushv4 %improvement
> >> > 1VM 48.5800 46.8513 3.55846
> >> > 2VM 108.1823 104.6410 3.27346
> >> > 3VM 183.2733 163.3547 10.86825
> >> >
> >> > ebizzy(higher is better)
> >> > ========================
> >> > base pvflushv4 %improvement
> >> > 1VM 2414.5000 2089.8750 -13.44481
> >> > 2VM 2167.6250 2371.7500 9.41699
> >> > 3VM 1600.1111 2102.5556 31.40060
> >> >
> >>
> >> The regression is worrying. We're improving the contended case at the
> >> cost of the non-contended case, this is usually the wrong thing to do.
> >> Do we have any clear idea of the cause of the regression?
> >>
> > Previous perf numbers suggest that in 1VM scenario flush_tlb_others_ipi
> > is around 2%, while for contented case its around 10%. That is what is
> > helping contended case.
>
> But what is causing the regression for the uncontended case?
>
Haven't been able to nail that, any clue on how to profile would help.

Regards
Nikunj