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

[Reeted <reeted@shiftmail.org>]

On 03/06/12 13:59, Stefan Hajnoczi wrote:
> On Mon, Mar 5, 2012 at 4:44 PM, Martin Mailand<martin@tuxadero.com>  wrote:
>> Am 05.03.2012 17:35, schrieb Stefan Hajnoczi:
>>
>>>> 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?
>>
>>
>> Hi Stefan,
>> all results are with "ondemand" except the one where I changed it to
>> "performance"
>>
>> 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
R.