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Date: Tue, 10 Nov 2009 16:43:38 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] Re: virtio: Add memory statistics reporting to the
	balloon driver
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Anthony Liguori <aliguori@us.ibm.com>, linux-kernel@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Adam Litke <agl@us.ibm.com>

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).

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