Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler

[Raghavendra K T]

On 07/11/2012 02:30 PM, Avi Kivity wrote:
> On 07/10/2012 12:47 AM, Andrew Theurer wrote:
> > For the cpu threads in the host that are actually active (in this case
> > 1/2 of them), ~50% of their time is in kernel and ~43% in guest.  This
> > is for a no-IO workload, so that's just incredible to see so much cpu
> > wasted.  I feel that 2 important areas to tackle are a more scalable
> > yield_to() and reducing the number of pause exits itself (hopefully by
> > just tuning ple_window for the latter).
>
> One thing we can do is autotune ple_window.  If a ple exit fails to wake
> anybody (because all vcpus are either running, sleeping, or in ple
> exits) then we deduce we are not overcommitted and we can increase the
> ple window.  There's the question of how to decrease it again though.

I see some problem here, If I interpret situation correctly. What
happens if we have two guests with one VM having no over-commit and 
other with high over-commit. (except when we have gang scheduling).

Rather we should have something tied to VM rather than rigid PLE
window.

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