Re: Network I/O performance

Herbert Xu
2009-05-19T01:30:32Z

On Mon, May 18, 2009 at 12:14:34AM +0300, Avi Kivity wrote:
>
>> No, I am measuring UDP throughput performance. I have now tried using a
>> different NIC model, and the e1000 model seems to achieve slightly
>> better performance (CPU goes up to 110% only though). I have also been
>> running virtio now, and while its performance with 2.6.20 was very poor
>> too, when changing the guest kernel to 2.6.30, I get a reasonable
>> performance and higher CPU utilization (e.g. it goes up to 180-190%). I
>> have to throttle the incoming bandwidth though, because as soon as I go
>> over a certain threshold, CPU goes back down to 90% and throughput goes
>> down too.
>
> Yes, there's a known issue with UDP, where we don't report congestion
> and the queues start dropping packets. There's a patch for tun queued
> for the next merge window; you'll need a 2.6.31 host for that IIRC
> (Herbert?)

It should be in 2.6.30 in fact. However, this is for outbound
traffic only since inbound traffic shouldn't have this problem
of the guest sending faster than the wire.

Cheers,
--
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