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Re: [Qemu-devel] Re: virtio: Add memory statistics reporting to the ball

From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: virtio: Add memory statistics reporting to the balloon driver
Date: Tue, 10 Nov 2009 08:58:27 -0600
User-agent: Thunderbird (X11/20090825)

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.


Anthony Liguori

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