On Sun, Dec 12, 2010 at 10:56:34PM +0200, Michael S. Tsirkin wrote: > 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.
Another datapoint where I see a regression is with 4000 byte messages for guest to host traffic. ioeventfd=off set_up_server could not establish a listen endpoint for port 12865 with family AF_UNSPEC TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.4 (11.0.0.4) 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 4000 10.00 7717.56 98.80 15.11 1.049 2.566 ioeventfd=on TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.4 (11.0.0.4) 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 4000 10.00 3965.86 87.69 15.29 1.811 5.055 -- MST
