Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenariosin PLE handler

[Avi Kivity]

On 09/28/2012 01:40 PM, Andrew Theurer wrote:
>> 
>> >>
>> >> IIRC, with defer preemption :
>> >> we will have hook in spinlock/unlock path to measure depth of lock held,
>> >> and shared with host scheduler (may be via MSRs now).
>> >> Host scheduler 'prefers' not to preempt lock holding vcpu. (or rather
>> >> give say one chance.
>> >
>> > A downside is that we have to do that even when undercommitted.
> 
> Hopefully vcpu preemption is very rare when undercommitted, so it should
> not happen much at all.

As soon as you're preempted, you're effectively overcommitted (even if
the system as a whole is undercommitted).  What I meant was that you
need to communicate your lock state to the host, and with fine-grained
locking this can happen a lot.  It may be as simple as an
increment/decrement instruction though.



-- 
error compiling committee.c: too many arguments to function
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