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

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

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.

> 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).
> 


-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization

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