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Date: Tue, 21 Feb 2012 17:45:08 +0100
From: Dongsu Park <dongsu.park@profitbricks.com>
Message-ID: <20120221164508.GB950@gmail.com>
References: <20120210143639.GA17883@gmail.com> <87sjifd2sw.fsf@rustcorp.com.au>
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Subject: Re: [Qemu-devel] virtio-blk performance regression and qemu-kvm
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To: Rusty Russell <rusty@rustcorp.com.au>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org

Hi Rusty,

On 13.02.2012 10:25, Rusty Russell wrote:
> On Fri, 10 Feb 2012 15:36:39 +0100, Dongsu Park <dongsu.park@profitbricks.com> wrote:
> > Hi,
> > 
> > Recently I observed performance regression regarding virtio-blk,
> > especially different IO bandwidths between qemu-kvm 0.14.1 and 1.0.
> > So I want to share the benchmark results, and ask you what the reason
> > would be.
> 
> Interesting.  There are two obvious possibilities here.  One is that
> qemu has regressed, the other is that virtio_blk has regressed; the new
> qemu may negotiate new features.  Please do the following in the guest
> with old and new qemus:
> 
> cat /sys/class/block/vdb/device/features
> 
> (eg, here that gives: 0010101101100000000000000000100e0).

I did that on guest VM, using both qemu-kvm 0.14.1 and 1.0.
(cat /sys/class/block/vdb/device/features)

using qemu-kvm 0.14.1:

0010101101100000000000000000100000000000000000000000000000000000

using qemu-kvm 1.0:

0010101101100000000000000000110000000000000000000000000000000000

>>From my understanding, both of them have the same virtio features.
Please correct me if I'm wrong.

Regards,
Dongsu