Re: [Qemu-devel] virtio-blk performance regression and qemu-kvm

[Dongsu Park]

Hi Rusty,

On 13.02.2012 10:25, Rusty Russell wrote:
> On Fri, 10 Feb 2012 15:36:39 +0100, Dongsu Park <address@hidden> 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