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Subject: Re: virtio ring layout changes for optimal single-stream performance
On Thu, Jan 21, 2016 at 04:38:36PM +0100, Cornelia Huck wrote: > On Thu, 21 Jan 2016 15:39:26 +0200 > "Michael S. Tsirkin" <firstname.lastname@example.org> wrote: > > > Hi all! > > I have been experimenting with alternative virtio ring layouts, > > in order to speed up single stream performance. > > > > I have just posted a benchmark I wrote for the purpose, and a (partial) > > alternative layout implementation. This achieves 20-40% reduction in > > virtio overhead in the (default) polling mode. > > > > http://article.gmane.org/gmane.linux.kernel.virtualization/26889 > > > > The layout is trying to be as simple as possible, to reduce > > the number of cache lines bouncing between CPUs. > > Some kind of diagram or textual description would really help to review > this. > > > > > For benchmarking, the idea is to emulate virtio in user-space, > > artificially adding overhead for e.g. signalling to match what happens > > in case of a VM. > > Hm... is this overhead comparable enough between different platform so > that you can get a halfway realistic scenario? On x86 is seems pretty stable. It's a question of setting VMEXIT_CYCLES and VMENTRY_CYCLES correctly. > What about things like > endianness conversions? I didn't bother with them yet. > > > > I'd be very curious to get feedback on this, in particular, some people > > discussed using vectored operations to format virtio ring - would it > > conflict with this work? > > > > You are all welcome to post enhancements or more layout alternatives as > > patches. > > Let me see if I can find time to experiment a bit.