On Sun, Dec 12, 2010 at 10:42:28PM +0200, Michael S. Tsirkin wrote: > On Sun, Dec 12, 2010 at 10:41:28PM +0200, Michael S. Tsirkin wrote: > > On Sun, Dec 12, 2010 at 03:02:04PM +0000, Stefan Hajnoczi wrote: > > > See below for the v5 changelog. > > > > > > Due to lack of connectivity I am sending from GMail. Git should retain my > > > stefa...@linux.vnet.ibm.com From address. > > > > > > Virtqueue notify is currently handled synchronously in userspace virtio. > > > This > > > prevents the vcpu from executing guest code while hardware emulation code > > > handles the notify. > > > > > > On systems that support KVM, the ioeventfd mechanism can be used to make > > > virtqueue notify a lightweight exit by deferring hardware emulation to the > > > iothread and allowing the VM to continue execution. This model is > > > similar to > > > how vhost receives virtqueue notifies. > > > > > > The result of this change is improved performance for userspace virtio > > > devices. > > > Virtio-blk throughput increases especially for multithreaded scenarios and > > > virtio-net transmit throughput increases substantially. > > > > Interestingly, I see decreased throughput for small message > > host to get netperf runs. > > > > The command that I used was: > > netperf -H $vguest -- -m 200 > > > > And the results are: > > - with ioeventfd=off > > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.104 > > (11.0.0.104) port 0 AF_INET : demo > > Recv Send Send Utilization Service > > Demand > > Socket Socket Message Elapsed Send Recv Send Recv > > Size Size Size Time Throughput local remote local > > remote > > bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB > > > > 87380 16384 200 10.00 3035.48 15.50 99.30 6.695 > > 2.680 > > > > - with ioeventfd=on > > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.104 > > (11.0.0.104) port 0 AF_INET : demo > > Recv Send Send Utilization Service > > Demand > > Socket Socket Message Elapsed Send Recv Send Recv > > Size Size Size Time Throughput local remote local > > remote > > bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB > > > > 87380 16384 200 10.00 1770.95 18.16 51.65 13.442 > > 2.389 > > > > > > Do you see this behaviour too? > > Just a note: this is with the patchset ported to qemu-kvm.
And just another note: the trend is reversed for larged messages, e.g. with 1.5k messages ioeventfd=on outputforms ioeventfd=off. > > -- > > MST