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[Qemu-devel] Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into
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From: |
Jes Sorensen |
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Subject: |
[Qemu-devel] Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself |
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Date: |
Mon, 31 May 2010 09:36:00 +0200 |
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User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-2.fc12 Lightning/1.0b2pre Thunderbird/3.0.4 |
On 05/30/10 13:22, Michael S. Tsirkin wrote:
> On Fri, May 28, 2010 at 11:56:54AM +0200, Jes Sorensen wrote:
>> It looks pretty good to me, however one thing I have been thinking of
>> while reading through it:
>>
>> Rather than storing a pointer within the ring struct, pointing into a
>> position within the same struct. How about storing a byte offset instead
>> and using a cast to get to the pointer position? That would avoid the
>> pointer dereference, which is less effective cache wise and harder for
>> the CPU to predict.
>>
>> Not sure whether it really matters performance wise, just a thought.
>
> I think this won't work: when PUBLUSH_USED_IDX is negotiated,
> the pointer is to within the ring.
Hmmm shame, it would be a nice optimization.
Maybe it's time to introduce the v2 ring format, rather than having
adding more kludges to the existing one?
Cheers,
Jes