On Mon, Dec 13, 2010 at 05:57:28PM +0000, Stefan Hajnoczi wrote: > On Mon, Dec 13, 2010 at 4:28 PM, Stefan Hajnoczi <stefa...@gmail.com> wrote: > > On Mon, Dec 13, 2010 at 4:12 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > >> On Mon, Dec 13, 2010 at 03:27:06PM +0000, Stefan Hajnoczi wrote: > >>> On Mon, Dec 13, 2010 at 1:36 PM, Michael S. Tsirkin <m...@redhat.com> > >>> wrote: > >>> > On Mon, Dec 13, 2010 at 03:35:38PM +0200, Michael S. Tsirkin wrote: > >>> >> On Mon, Dec 13, 2010 at 01:11:27PM +0000, Stefan Hajnoczi wrote: > >>> >> > Fresh results: > >>> >> > > >>> >> > 192.168.0.1 - host (runs netperf) > >>> >> > 192.168.0.2 - guest (runs netserver) > >>> >> > > >>> >> > host$ src/netperf -H 192.168.0.2 -- -m 200 > >>> >> > > >>> >> > ioeventfd=on > >>> >> > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.0.2 > >>> >> > (192.168.0.2) port 0 AF_INET > >>> >> > Recv Send Send > >>> >> > Socket Socket Message Elapsed > >>> >> > Size Size Size Time Throughput > >>> >> > bytes bytes bytes secs. 10^6bits/sec > >>> >> > 87380 16384 200 10.00 1759.25 > >>> >> > > >>> >> > ioeventfd=off > >>> >> > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.0.2 > >>> >> > (192.168.0.2) port 0 AF_INET > >>> >> > Recv Send Send > >>> >> > Socket Socket Message Elapsed > >>> >> > Size Size Size Time Throughput > >>> >> > bytes bytes bytes secs. 10^6bits/sec > >>> >> > > >>> >> > 87380 16384 200 10.00 1757.15 > >>> >> > > >>> >> > The results vary approx +/- 3% between runs. > >>> >> > > >>> >> > Invocation: > >>> >> > $ x86_64-softmmu/qemu-system-x86_64 -m 4096 -enable-kvm -netdev > >>> >> > type=tap,id=net0,ifname=tap0,script=no,downscript=no -device > >>> >> > virtio-net-pci,netdev=net0,ioeventfd=on|off -vnc :0 -drive > >>> >> > if=virtio,cache=none,file=$HOME/rhel6-autobench-raw.img > >>> >> > > >>> >> > I am running qemu.git with v5 patches, based off > >>> >> > 36888c6335422f07bbc50bf3443a39f24b90c7c6. > >>> >> > > >>> >> > Host: > >>> >> > 1 Quad-Core AMD Opteron(tm) Processor 2350 @ 2 GHz > >>> >> > 8 GB RAM > >>> >> > RHEL 6 host > >>> >> > > >>> >> > Next I will try the patches on latest qemu-kvm.git > >>> >> > > >>> >> > Stefan > >>> >> > >>> >> One interesting thing is that I put virtio-net earlier on > >>> >> command line. > >>> > > >>> > Sorry I mean I put it after disk, you put it before. > >>> > >>> I can't find a measurable difference when swapping -drive and -netdev. > >> > >> One other concern I have is that we are apparently using > >> ioeventfd for all VQs. E.g. for virtio-net we probably should not > >> use it for the control VQ - it's a waste of resources. > > > > One option is a per-device (block, net, etc) bitmap that masks out > > virtqueues. Is that something you'd like to see? > > > > I'm tempted to mask out the RX vq too and see how that affects the > > qemu-kvm.git specific issue. > > As expected, the rx virtqueue is involved in the degradation. I > enabled ioeventfd only for the TX virtqueue and got the same good > results as userspace virtio-net. > > When I enable only the rx virtqueue, performs decreases as we've seen above. > > Stefan
Interesting. In particular this implies something's wrong with the queue: we should not normally be getting notifications from rx queue at all. Is it running low on buffers? Does it help to increase the vq size? Any other explanation? -- MST