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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