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

Stefan Hajnoczi
2010-12-01T11:44:11Z

On Mon, Nov 15, 2010 at 11:20 AM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> On Sun, Nov 14, 2010 at 12:19 PM, Avi Kivity <avi@redhat.com> wrote:
>> On 11/14/2010 01:05 PM, Avi Kivity wrote:
>>>>
>>>> I agree, but let's enable virtio-ioeventfd carefully because bad code
>>>> is out there.
>>>
>>>
>>> Sure.  Note as long as the thread waiting on ioeventfd doesn't consume too
>>> much cpu, it will awaken quickly and we won't have the "transaction per
>>> timeslice" effect.
>>>
>>> btw, what about virtio-blk with linux-aio?  Have you benchmarked that with
>>> and without ioeventfd?
>>>
>>
>> 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.

Stefan