On Wed, Mar 03, 2010 at 12:54:25AM -0800, David Stevens wrote: > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote on 03/02/2010 11:54:32 PM: > > > On Tue, Mar 02, 2010 at 04:20:03PM -0800, David Stevens wrote: > > > These patches add support for mergeable receive buffers to > > > vhost-net, allowing it to use multiple virtio buffer heads for a > single > > > receive packet. > > > +-DLS > > > > > > > > > Signed-off-by: David L Stevens <dlstevens@xxxxxxxxxx> > > > > Do you have performance numbers (both with and without mergeable buffers > > in guest)? > > Michael, > Nothing formal. I did some TCP single-stream throughput tests > and was seeing 20-25% improvement on a laptop (ie, low-end hardware). > That actually surprised me; I'd think it'd be about the same, except > maybe in a test that has mixed packet sizes. Comparisons with the > net-next kernel these patches are for showed only ~10% improvement. > But I also see a lot of variability both among different > configurations and with the same configuration on different runs. > So, I don't feel like those numbers are very solid, and I haven't > yet done any tests on bigger hardware. Interesting. Since the feature in question is billed first of all a performance optimization, I think we might need some performance numbers as a motivation. Since the patches affect code paths when mergeable RX buffers are disabled as well, I guess the most important point would be to verify whether there's increase in latency and/or CPU utilization, or bandwidth cost when the feature bit is *disabled*. > 2 notes: I have a modified version of qemu to get the VHOST_FEATURES > flags, including the mergeable RX bufs flag, passed to the guest; I'll > be working with your current qemu git trees next, if any changes are > needed to support it there. This feature also seems to conflict with zero-copy rx patches from Xin Xiaohui (subject: Provide a zero-copy method on KVM virtio-net) these are not in a mergeable shape yet, so this is not a blocker, but I wonder what your thoughts on the subject are: how will we do feature negotiation if some backends don't support some features? > Second, I've found a missing initialization in the patches I > sent on the list, so I'll send an updated patch 2 with the fix, If you do, any chance you could use git send-email for this? > and qemu patches when they are ready (plus any code-review comments > incorporated). > Pls take a look here as well http://www.openfabrics.org/~mst/boring.txt -- 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
