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


From: Stefan Hajnoczi
Subject: [Qemu-devel] Re: [PATCH v5 0/4] virtio: Use ioeventfd for virtqueue notify
Date: Mon, 13 Dec 2010 17:57:28 +0000

On Mon, Dec 13, 2010 at 4:28 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Mon, Dec 13, 2010 at 4:12 PM, Michael S. Tsirkin <address@hidden> 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 <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.
>>
>> 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



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