Re: [Qemu-devel] Re: [PATCH 2/3] virtio-pci: Use ioeventfd for virtqueue notify

[Avi Kivity]

On 12/01/2010 01:44 PM, Stefan Hajnoczi wrote:
> >>
> >>  And, what about efficiency?  As in bits/cycle?
> >
> >  We are running benchmarks with this latest patch and will report results.
>
> Full results here (thanks to Khoa Huynh):
>
> http://wiki.qemu.org/Features/VirtioIoeventfd
>
> The host CPU utilization is scaled to 16 CPUs so a 2-3% reduction is
> actually in the 32-48% range for a single CPU.
>
> The guest CPU utilization numbers include an efficiency metric: %vcpu
> per MB/sec.  Here we see significant improvements too.  Guests that
> previously couldn't get more CPU work done now have regained some
> breathing space.

Thanks for those numbers.  The guest improvements were expected, but the 
host numbers surprised me.  Do you have an explanation as to why total 
host load should decrease?

Seems to me the host is doing more work, and doing it less efficiently 
(by ping-ponging requests to another thread).

In any case, looks like good improvement with no downsides.

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