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Date: Mon, 05 Mar 2012 17:13:20 +0100
From: Martin Mailand <martin@tuxadero.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: stefanha@gmail.com, qemu-devel@nongnu.org, kvm@vger.kernel.org

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


2. Test on AMD Istanbul without powermanagement activated.

v0.14.1
bw=53167KB/s iops=13291
bw=61386KB/s iops=15346

v1.0
bw=43599KB/s iops=10899
bw=46288KB/s iops=11572

master
bw=60678KB/s iops=15169
bw=62733KB/s iops=15683

-martin