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

[cauchy-love]

I have tried your qemu cammand line but got no luck (the embedded os have no 
virtio support but this is not the problem i think). The problem probably lies 
in the host kernel version as it is the only difference for my tests. I traced 
the guest kernel and found the ATA drivers always used non-DMA mode (CentOS 7 
and CentOS 6.5 are the same at this point). 
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

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