Re: [PATCH 0/9][RFC] KVM virtio_net performance

Dor Laor
2008-07-25T21:31:30Z

Mark McLoughlin wrote:
> On Thu, 2008-07-24 at 15:56 -0500, Anthony Liguori wrote:
>
>> Hi Mark,
>>
>> Mark McLoughlin wrote:
>>
>>> Hey,
>>> Here's a bunch of patches attempting to improve the performance
>>> of virtio_net. This is more an RFC rather than a patch submission
>>> since, as can be seen below, not all patches actually improve the
>>> perfomance measurably.
>>>
>>>
>> I'm still seeing the same problem I saw with my patch series. Namely,
>> dhclient fails to get a DHCP address. Rusty noticed that RX has a lot
>> more packets received then it should so we're suspicious that we're
>> getting packet corruption.
>>
>
> I've just tried bridging to my physical LAN and DHCP seems to be working
> fine.
>
> Which reminds me, though - doing this makes host->guest throughput drop
> to well below pre-GSO figures. GSO appears to be disabled while there's
> a physical interface on the bridge. If I remove eth0, the figures jump
> right back up again.
>
> I also just noticed that the GSO patch breaks e1000 because it
> unconditionally sets IFF_VNET_HDR. Will fix that up.
>
>
>> Configuring the tap device with a static address, here's what I get with
>> iperf:
>>
>> w/o patches:
>>
>> guest->host: 625 Mbits/sec
>> host->guest: 825 Mbits/sec
>>
>> w/patches
>>
>> guest->host: 2.02 Gbits/sec
>> host->guest: 1.89 Gbits/sec
>>
>> guest lo: 4.35 Gbits/sec
>> host lo: 4.36 Gbits/sec
>>
>
> I tried iperf at one point and was getting really low figures; not sure
> why.
>
>
Older iperf (~2.0.2) has locking vs yield bug and consumes lots of cpu.
In 2.0.4 it is fixed. Can that be the difference?
> Apart from your iperf figures being lower than my netperf figures, it
> also contradicts what I was seeing - namely guest->host beating
> host->guest before the patches and host->guest beating guest->host after
> the patches.
>
> It could all just be down to the length of the tx timer. If you try
> adjusting that does it help?
>
>
>> This is with KVM GUEST configured FWIW.
>>
>
> Yep, same here.
>
> Cheers,
> Mark.
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>