Re: [kvm-ppc-devel] virtio-net working on PowerPC KVM

Alexander Graf
2008-03-31T07:45:18Z

On Mar 31, 2008, at 6:52 AM, Christian Ehrhardt wrote:

> Avi Kivity wrote:
>> Hollis Blanchard wrote:
>>> I'm pleased to report that we now have working network support in
>>> the
>>> guest, via the virtio-net driver. In fact, we can use NFS for the
>>> guest's root filesystem. :) Boot log attached.
>>>
>>>
>>
>> Congrats!
>>
>>> The bad news is that it's very slow, but the good news is that
>>> it's nice
>>> to be improving performance rather than debugging mysterious
>>> crashes... ;)
>>>
>>> With this milestone reached, in the near future I intend to start
>>> sending patches to Avi and linuxppc-dev for review, hopefully for
>>> inclusion in 2.6.26. However, I do want to see if we can improve the
>>> performance a little bit first...
>>>
>>
>> Low virtio net performance may be due to the virtio net host timer.
>> What's your guest/host ping latency?
>
> I would be happy about 0.25ms atm :-). The current ping latency to
> the Host or other PC's is around 7-8ms (native sys is ~0.15ms).
> We are investigating performance improvements in general and also
> some changes in the setup e.g. booting from virtio-block as
> alternative for some speedup.

I am experiencing 7-8ms ping latencies (native 0.1ms) on x86_64 as
well, when pinging the virtual machine. Maybe it's not related to
PowerPC? Is it supposed to be that slow?

>
>
>> Even if you have a good hrtimer implementation, I think you'll see
>> 0.25ms latency, and that may be enough to slow down nfs.
>> Unfortunately
>> virtio is tuned for throughput at this time (it should be easy to
>> disable the timer when we detect the queue is usually empty).
>>

Alex