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DateTue, 10 Nov 2009 08:58:27 -0600
FromAnthony Liguori <>
SubjectRe: [Qemu-devel] Re: virtio: Add memory statistics reporting to the balloon driver
Avi Kivity wrote:
> On 11/10/2009 04:36 PM, Anthony Liguori wrote:
>>
>>> A stats vq might solve this more cleanly?
>>
>> actual and target are both really just stats. Had we implemented
>> those with a vq, I'd be inclined to agree with you but since they're
>> implemented in the config space, it seems natural to extend the
>> config space with other stats.
>>
>
> There is in fact a difference; actual and target are very rarely
> updated, while the stats are updated very often. Using a vq means a
> constant number of exits per batch instead of one exit per statistic.
> If the vq is host-driven, it also allows the host to control the
> update frequency dynamically (i.e. stop polling when there is no
> memory pressure).

I'm not terribly opposed to using a vq for this. I would expect the
stat update interval to be rather long (10s probably) but a vq works
just as well.

--
Regards,

Anthony Liguori



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