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

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] virtio-blk performance regression and qemu-kvm
Date: Mon, 5 Mar 2012 16:35:00 +0000

On Mon, Mar 5, 2012 at 4:13 PM, Martin Mailand <address@hidden> wrote:
> Am 10.02.2012 15:36, schrieb Dongsu Park:
>> 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.
> Hi,
> I think I found the problem, there is no regression in the code.
> I think the problem is, that qmeu-kvm with the IO-Thread enabled doesn't
> produce enough cpu load to get the core to a higher cpu frequency, because
> the load is distributed to two threads.
> If I change the cpu governor to "performance" the result from the master
> branch is better than from the v0.14.1 branch.
> I get the same results on a serversystem without powermanagment activated.
> @Dongsu Could you confirm those findings?
> 1. Test on i7 Laptop with Cpu governor "ondemand".
> v0.14.1
> bw=63492KB/s iops=15873
> bw=63221KB/s iops=15805
> v1.0
> bw=36696KB/s iops=9173
> bw=37404KB/s iops=9350
> master
> bw=36396KB/s iops=9099
> bw=34182KB/s iops=8545
> Change the Cpu governor to "performance"
> master
> bw=81756KB/s iops=20393
> bw=81453KB/s iops=20257

Interesting finding.  Did you show the 0.14.1 results with
"performance" governor?


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