On Mon, 2011-11-28 at 22:17 +0200, Sasha Levin wrote: > On Mon, 2011-11-28 at 20:49 +0200, Pekka Enberg wrote: > > On Mon, Nov 28, 2011 at 7:54 PM, Sasha Levin <levinsasha928@xxxxxxxxx> wrote: > > > Indirect buffers are ring descriptors which point to more (even more) > > > descriptors. > > > > > > This can be used to increase the effective ring capacity, which helps the > > > guest to batch large requests - very useful for blk devices. > > > > > > This patch also enables indirect buffers for virtio-net and virtio-blk. > > > > > > The patch is based on the lguest's code which does the same. > > > > > > Signed-off-by: Sasha Levin <levinsasha928@xxxxxxxxx> > > > > In what exact way is it useful? Improved throughput? Will this have > > negative impact on virtio block or virtio net latency? > > The total size of requests is limited by the size of the virtio ring. > This makes it hard to squeeze large requests (like the ones you usually > see with blk devices) into the ring. This patch simply makes each entry > in the virtio ring point to another descriptor list, thus it allows to > squeeze much more requests into a singe virtio ring. > > It shouldn't hurt latency. > > I tried getting benchmarks with it, but the results I get from fio are > all over the place and I can't seem to get a steady result (bad sign for > my poor spindle disk). btw, on an unrelated subject, I think that with this patch we've fully covered the virtio spec, and as far as I know it's the first userspace implementation which covers the entire spec :) -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
