Re: [Qemu-devel] Greate difference of disk I/O performance for guest on Qemu-2.30 of CentOS.

[cauchy-love]

the iozone  command line is:
./iozone -i 0 -i 1 -f ./iotmp -Rab ./iotmp.xls -g 8G -n 4G -c

The problem is why the performance difference is so big for different linux 
kernels. The guest's io performance test is by both FTP tools and raw write, 
which demonstrate the much lower performance of  Centos 7 (1/10 of that on 
Centos 6.5). And how can I debug this problem?
 
Thanks again for your help.

Yi



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在 2015-06-16 21:05:39，"Stefan Hajnoczi" <address@hidden> 写道：
>On Mon, Jun 15, 2015 at 09:14:52PM +0800, cauchy-love wrote:
>>    I am running a embedded OS on Qemu-2.3.0. However I found that the I/O 
>> performance was quite different for different CentOS release (CentOS 6.5 and 
>> CentOS 7.0). The CentOS 6.5 uses linux-2.6.32 while the CentOS 7.0 uses 
>> linux-3.10.0. The I/O throughput (write) of the former (CentOS 6.5) is about 
>> ten times of that on the latter (CentOS 7.0). All configurations are the 
>> same except the kernel version. And the command line is as following:
>>                       # qemu-kvm -m 2G -smp 4 -enable-kvm -hda guest.img ...
>>  The I/O throughput of the host is almost the same for these two different 
>> kernels, as tested by Iozone tool. Actually, I found that the IO throughput 
>> degraded significantly since the 3.4 or later kernel version. I also tried 
>> different qemu versions such as qemu-1.5.3, qemu-2.1.3 but got no 
>> improvements.
>
>Please post the iozone command-line you are using and the output.
>
>Your QEMU command-line uses the IDE storage controller, which is not
>optimized for performance.  Usually virtio-blk is used when good
>performance is required:
>
>  -drive if=virtio,cache=none,format=raw,aio=native,file=guest.img
>
>The guest OS needs virtio-blk device drivers in order for this to work.
>
>Stefan