Re: [Qemu-devel] question about performance of dataplane

[Anthony Liguori <anthony@codemonkey.ws>]

Zhangleiqiang <zhangleiqiang@huawei.com> writes:

> Hi, Stefan：
>
> 	I have done some testing to compare the performance of dataplane and non-dataplane.  But the result did not meet my expectations, the performance of disk with dataplane enabled did not have advantage over non-dataplane. 
>
> 	The following  contains the  environment info and testing results.  Does my testing method or testing environment have something wrong ?  Could you give me some advice?  I can provide more information if need.
>
>
> 1. Environment:
> 	a). Qemu 1.4 master branch
> 	b). kernel:  3.5.0-2.fc17.x86_64
>          c). virtual disks location:  the same local SATA harddisk
> 	with ext4 fs

I doubt you'll see any performance difference with a single SATA drive.
There's no real parallelism possible as you have exactly one spindle
available.

> datasize/RW_Ratio		IOPS_dataplane	IOPS_non_dataplane	MBPS_dataplane	MBPS_non_dataplane
> 	16K/0%			294.094948			293.609606			4.595234			4.58765
> 	16K/25%			283.096745			281.649258			4.423387			4.40077
> 	16K/75%			316.039801			309.585336			4.938122			4.837271
> 	32K/0%			257.529537			258.806128			8.047798			8.087692
> 	32K/25%			253.729281			253.756673			7.92904			7.929896
> 	32K/75%			292.384568			280.991434			9.137018			8.780982
> 	4K/0%			321.599352			324.116063			1.256247			1.266078
> 	4K/25%			309.906635			309.294278			1.210573			1.208181
> 	4K/75%			350.168882
> 	350.772329			1.367847
> 	1.370204


You are getting 300 MB/s to a single SATA disk?  I strongly suspect
you are seeing cache interaction.  I'd suggest disabling WCE on the disk
if you're going to benchmark like this.

I'd also guess 300 MB/s is what you're maxing out at with native too.
So presumably normal virtio-blk is already getting close to native
performance.  dataplane certainly isn't going to give you better than
native performance :-)

Regards,

Anthony Liguori

>
>
>
> ----------
> Leiqzhang
>
> Best Regards
>
>
>> 发件人: qemu-devel-bounces+zhangleiqiang=huawei.com@nongnu.org [mailto:qemu-devel-bounces+zhangleiqiang=huawei.com@nongnu.org] 代表 leiqzhang
>> 发送时间: 2013年3月28日 12:03
>> 收件人: Stefan Hajnoczi
>> 抄送: pbonzini@redhat.com; qemu-devel@nongnu.org; stefanha@redhat.com; 张 磊强
>> 主题: [Qemu-devel] 回复： dataplane bug: fail to start Windows VM with dataplane enable
>> 
>> Hi, Stefan:
>> 
>>     Thank for your reply and patch. I have done the test for Windows 7, Windows 2003, and fedora.
>> 
>>      The patch has fixed the problem now, thanks. 
>> 
>> -- 
>> leiqzhang
>> Sent by  Sparrow
>> 
>> 在 2013年3月27日星期三，23:41，Stefan Hajnoczi 写道：
>> On Tue, Mar 26, 2013 at 11:10:35PM +0800, 张磊强 wrote:
>> Hi, Paolo && Stefan:
>> 
>> When I test the dataplane feature with qemu master, I find that
>> Windows (Windows 7 and Windows 2003) VM will hang if dataplane is
>> enabled. But if I try to start a Fedora VM, it can start normally.
>> 
>> The command I boot QEMU is:
>> x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 1024 -smp 2 -drive
>> file=win7.img,if=none,id=drive-virtio-disk,format=raw,cache=none,aio=native
>> -device virtio-blk-pci,config-wce=off,scsi=off,x-data-plane=on,drive=drive-virtio-disk,id=virtio-disk
>> 
>> I found the similar bug has reported some days ago:
>> http://lists.nongnu.org/archive/html/qemu-devel/2013-03/msg02200.html
>> . And a patch for this bug has already committed by Paolo at Mar 13:
>> http://lists.nongnu.org/archive/html/qemu-devel/2013-03/msg02200.html
>> .
>> 
>> But it cannot work under my environment. Could you give me some advise
>> to debug this problem ? I can provide more information if need.
>> 
>> I sent a fix and CCed you on the patch. Please test it if you have
>> time.
>> 
>> Stefan
>>