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Date: Wed, 1 Dec 2010 11:44:10 +0000
Message-ID: <AANLkTikw4V0UJyVs9StXCSkcHfKRxNBsaY6eZ4-P2y6d@mail.gmail.com>
Subject: Re: [Qemu-devel] Re: [PATCH 2/3] virtio-pci: Use ioeventfd for
	virtqueue notify
From: Stefan Hajnoczi <stefanha@gmail.com>
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To: Avi Kivity <avi@redhat.com>
Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, Christoph Hellwig <hch@infradead.org>, Khoa Huynh <khoa@us.ibm.com>

On Mon, Nov 15, 2010 at 11:20 AM, Stefan Hajnoczi <stefanha@gmail.com> wrot=
e:
> 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. =A0Note as long as the thread waiting on ioeventfd doesn't consum=
e 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? =A0Have you benchmarked that=
 with
>>> and without ioeventfd?
>>>
>>
>> And, what about efficiency? =A0As 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