On Thu, Jan 27, 2011 at 10:44:34AM -0800, Shirley Ma wrote: > On Wed, 2011-01-26 at 17:17 +0200, Michael S. Tsirkin wrote: > > I am seeing a similar problem, and am trying to fix that. > > My current theory is that this is a variant of a receive livelock: > > if the application isn't fast enough to process > > incoming data, the guest net stack switches > > from prequeue to backlog handling. > > > > One thing I noticed is that locking the vhost thread > > and the vcpu to the same physical CPU almost doubles the > > bandwidth. Can you confirm that in your setup? > > > > My current guess is that when we lock both to > > a single CPU, netperf in guest gets scheduled > > slowing down the vhost thread in the host. > > > > I also noticed that this specific workload > > performs better with vhost off: presumably > > we are loading the guest less. > > I found similar issue for small message size TCP_STREAM test when guest > as TX. I found when I slow down TX, the BW performance will be doubled > for 1K to 4K message size. > > Shirley Interesting. In particular running vhost and the transmitting guest on the same host would have the effect of slowing down TX. Does it double the BW for you too? -- MST -- 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
