Re: 8bf00a529967dafbbb210b377c38a15834d1e979 - performance regression?

Gleb Natapov
2013-11-04T19:39:30Z

On Mon, Nov 04, 2013 at 09:30:42PM +0200, Michael S. Tsirkin wrote:
> On Thu, Oct 31, 2013 at 02:21:46AM +0200, Michael S. Tsirkin wrote:
> > commit 8bf00a529967dafbbb210b377c38a15834d1e979:
> > " KVM: VMX: add support for switching of PERF_GLOBAL_CTRL " was
> > as far as I can tell supposed to bring about performance improvement
> > on hardware that supports it?
> > Instead it seems to make the typical case (not running guest
> > under perf) a bit slower than it used to be.
> > the cost of VMexit goes up by about 50 cycles
> > on sandy bridge where the optimization in question
> > actually is activated.
> >
> > Why that's not a large regression, it's a far cry from
> > actually helping performance.
> >
> > So are we better off not using this feature?
> > What kind of workload is improved by this change?
>
> Ping.
I answer it already.

--
Gleb.