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? -- MST
