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Date: Wed, 22 Feb 2012 19:53:19 +0000
Message-ID: <CAJSP0QUKiKaKuQL46w3cycxL=cYgqUD=cc+MZCL=arKbMUZx0g@mail.gmail.com>
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] virtio-blk performance regression and qemu-kvm
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To: Dongsu Park <dongsu.park@profitbricks.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org

On Wed, Feb 22, 2012 at 4:48 PM, Dongsu Park
<dongsu.park@profitbricks.com> wrote:
>> Try turning ioeventfd off for the virtio-blk device:
>>
>> -device virtio-blk-pci,ioeventfd=3Doff,...
>>
>> You might see better performance since ramdisk I/O should be very
>> low-latency. =A0The overhead of using ioeventfd might not make it
>> worthwhile. =A0The ioeventfd feature was added post-0.14 IIRC. =A0Normal=
ly
>> it helps avoid stealing vcpu time and also causing lock contention
>> inside the guest - but if host I/O latency is extremely low it might
>> be faster to issue I/O from the vcpu thread.
>
> Thanks for the tip. I tried that too, but no success.

My guesses have all been wrong.  Maybe it's time to git bisect this instead=
 :).

Stefan