Re: 8bf00a529967dafbbb210b377c38a15834d1e979 - performance regression?

Michael S. Tsirkin
2013-11-04T19:27:49Z

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.
Let's revert 8bf00a529967dafbbb210b377c38a15834d1e979?
I see a small performance gain from reverting it ...

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MST