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

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Mar 6, 2012 at 10:07 PM, Reeted <reeted@shiftmail.org> wrote:
> 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...

It depends on the benchmark configuration.  virtio-blk is capable of
doing 100,000s of iops, I've seen results.  My guess is that you can
do >100,000 read iops with virtio-blk on a good machine and stock
qemu-kvm.

Stefan