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

[Rusty Russell]

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).

Thanks,
Rusty.