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

[Stefan Hajnoczi]

On Wed, Mar 7, 2012 at 2:21 PM, Reeted <address@hidden> wrote:
> On 03/07/12 09:04, Stefan Hajnoczi wrote:
>>
>> On Tue, Mar 6, 2012 at 10:07 PM, Reeted<address@hidden>  wrote:
>>>
>>> On 03/06/12 13:59, Stefan Hajnoczi wrote:
>>>>
>>>> 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.
>
>
> It's very difficult to configure, then.
> I also did benchmarks in the past, and I can confirm Martin and Dongsu
> findings of about 15 k IOPS with:
> qemu-kvm 0.14.1, Intel Westmere CPU, virtio-blk (kernel 2.6.38 on the guest,
> 3.0 on the host), fio, 4k random *reads* from the Host page cache (backend
> LVM device was fully in cache on the Host), writeback setting, cache dropped
> on the guest prior to benchmark (and insufficient guest memory to cache a
> significant portion of the device).
> If you can teach us how to reach 100 k IOPS, I think everyone would be
> grateful :-)

Sorry for being vague, I don't have the details.  I have CCed Khoa,
who might have time to describe a >100,000 iops virtio-blk
configuration.

Stefan