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Re: [Xen-devel] RFC v1: Xen block protocol overhaul - problem statement (with pictures!)

On Wed, 2013-01-23 at 15:21 +0000, Konrad Rzeszutek Wilk wrote:
> > Have you consider variable length requests? This would let the request
> > size scale with the number of segments required for that request, and
> > allow you to cache align the ends of the requests without wasting the
> > extra space that including the worst case number of segments would
> > imply. e.g. a small write would take 32-bytes (padded to 64 if you must)
> > and a larger one would take 196 (padded to 256). You should end up with
> > more efficient use of the space in the ring this way.
> Yes. If I recall right, the D) had it as "we could negotiate a proper 
> alignment for
> each request/response structure.". The idea is pretty much the same as yours
> - pad to the cacheline if the cacheline is bigger than the request or 
> response.

It would be interesting to know whether it is cache line bouncing or
smaller ring capacity (which padding reduces) which becomes the

My money is, unhelpfully, on "both, depending on workload".

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