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

From: Reeted
Subject: Re: [Qemu-devel] virtio-blk performance regression and qemu-kvm
Date: Tue, 06 Mar 2012 23:07:40 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111124 Thunderbird/8.0

On 03/06/12 13:59, Stefan Hajnoczi wrote:
On Mon, Mar 5, 2012 at 4:44 PM, Martin Mailand<address@hidden>  wrote:
Am 05.03.2012 17:35, schrieb Stefan Hajnoczi:

1. Test on i7 Laptop with Cpu governor "ondemand".
  bw=63492KB/s iops=15873
  bw=63221KB/s iops=15805

  bw=36696KB/s iops=9173
  bw=37404KB/s iops=9350

  bw=36396KB/s iops=9099
  bw=34182KB/s iops=8545

  Change the Cpu governor to "performance"
  bw=81756KB/s iops=20393
  bw=81453KB/s iops=20257
Interesting finding.  Did you show the 0.14.1 results with
"performance" governor?

Hi Stefan,
all results are with "ondemand" except the one where I changed it to

Do you want a v0.14.1 test with the governor on "performance"?
Yes, the reason why that would be interesting is because it allows us
to put the performance gain with master+"performance" into
perspective.  We could see how much of a change we get.

Me too, I would be interested in seeing 0.14.1 being tested with performance governor so to compare it to master with performance governor, to make sure that this is not a regression.

BTW, I'll take the opportunity to say that 15.8 or 20.3 k IOPS are very low figures compared to what I'd instinctively expect from a paravirtualized block driver. There are now PCIe SSD cards that do 240 k IOPS (e.g. "OCZ RevoDrive 3 x2 max iops") which is 12-15 times higher, for something that has to go through a real driver and a real PCI-express bus, and can't use zero-copy techniques. The IOPS we can give to a VM is currently less than half that of a single SSD SATA drive (60 k IOPS or so, these days). That's why I consider this topic of virtio-blk performances very important. I hope there can be improvements in this sector...

Thanks for your time

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