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

[Stefan Hajnoczi]

On Mon, Dec 13, 2010 at 1:36 PM, Michael S. Tsirkin <address@hidden> 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.

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