Messages in this thread | | | Date | Mon, 31 May 2010 16:29:50 +0300 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself |
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On Mon, May 31, 2010 at 09:36:00AM +0200, Jes Sorensen wrote: > 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
There has been discussion about a ring format that does not use indexes at all. My guess is that would be a good point for v2 ring format. But making that a product and tuning might take a while. So definitely something to keep in mind but I would not want that to block this optimization.
-- MST
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