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Date:	Tue, 10 Nov 2009 08:58:27 -0600
From:	Anthony Liguori <aliguori@...ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Anthony Liguori <anthony@...emonkey.ws>,
	Rusty Russell <rusty@...tcorp.com.au>, agl@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, qemu-devel@...gnu.org
Subject: Re: [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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