[Qemu-devel] Re: [PATCH v5 0/4] virtio: Use ioeventfd for virtqueue notify

["Michael S. Tsirkin" <mst@redhat.com>]

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 <mst@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.

> Can you run the same test with vhost?  I assume it still outperforms
> userspace virtio for small message sizes?  I'm interested because that
> also uses ioeventfd.
> 
> I am wondering if the iothread differences between qemu.git and
> qemu-kvm.git can explain the performance results we see.  In
> particular, qemu.git produces the same (high) throughput whether
> ioeventfd is on or off.
> 
> Stefan