Re: [Qemu-devel] [PATCH 0/2] Allocate mutiple clusters for VMDK I/O

[Ashijeet Acharya]

On Fri, Mar 24, 2017 at 8:54 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Thu, Mar 23, 2017 at 4:22 PM, Ashijeet Acharya
> <address@hidden> wrote:
>> On Thu, Mar 23, 2017 at 8:39 PM, Stefan Hajnoczi <address@hidden> wrote:
>>> On Tue, Mar 21, 2017 at 09:14:08AM +0000, Ashijeet Acharya wrote:
>>>> On Tue, 21 Mar 2017 at 13:21, Stefan Hajnoczi <address@hidden> wrote:
>>>>
>>>> > On Sat, Mar 11, 2017 at 11:54 AM, Ashijeet Acharya
>>>> > <address@hidden> wrote:
>>>> > > This series optimizes the I/O performance of VMDK driver.
>>>> > >
>>>> > > Patch 1 makes the VMDK driver to allocate multiple clusters at once.
>>>> > Earlier
>>>> > > it used to allocate cluster by cluster which slowed down its 
>>>> > > performance
>>>> > to a
>>>> > > great extent.
>>>> > >
>>>> > > Patch 2 changes the metadata update code to update the L2 tables for
>>>> > multiple
>>>> > > clusters at once.
>>
>> These are the commands I ran to test the write requests:
>>
>> My test file "test1.vmdk" is a 1G empty vmdk image created by using
>> 'qemu-img' tool.
>>
>> Before optimization:
>> $ ./bin/qemu-io -f vmdk --cache writeback
>> qemu-io> open -n -o driver=vmdk test1.vmdk
>> qemu-io> aio_write 0 128M
>> qemu-io> wrote 134217728/134217728 bytes at offset 0
>> 128 MiB, 1 ops; 0:00:16.46 (7.772 MiB/sec and 0.0607 ops/sec)
>>
>> After optimization:
>> $ ./bin/qemu-io -f vmdk --cache writeback
>> qemu-io> open -n -o driver=vmdk test1.vmdk
>> qemu-io> aio_write 0 128M
>> qemu-io> wrote 134217728/134217728 bytes at offset 0
>> 128 MiB, 1 ops; 0:00:08.19 (15.627 MiB/sec and 0.1221 ops/sec)
>>
>> Will these work?
>
> It is best to avoid --cache writeback in performance tests because
> using the host page cache puts the performance at the mercy of the
> kernel's page cache.

Okay, understood.

>
> I have run the following benchmark using "qemu-img bench":
>
> This patch series improves 128 KB sequential write performance to an
> empty VMDK file by 29%.
>
> Benchmark command: ./qemu-img bench -w -c 1024 -s 128K -d 1 -t none -f
> vmdk test.vmdk
>
> (Please include the 2 lines above in the next revision of the patch.)
>
Yes, I will do that. Also, this really helped me understand how to
actually test I/O optimizations.

Thanks for your help, this really solved my issue.

Ashijeet