Re: [PATCH 0/7] KVM: Suspend and cpu hotplug fixes

Avi Kivity
2007-05-27T10:21:01Z

Avi Kivity wrote:
> I estimate that that take_cpu_down will run for about a millisecond if
> there are a few hundred vcpus which have last run on the dying cpu (and
> that's an extreme case, which is not expected in normal operation).

I measured vmclear time on an uncached vmcs (which would be all except
for a handful which are cached on the cpu core) at 144 cycles. Assuming
a couple of cache misses for walking the list and accessing the vmcs,
we're at about 500 cycles per vcpu, or 250us @ 2GHz. So worst case is
significantly less than 1 ms.

Is this acceptable for take_cpu_down()?

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