Re: Performance comparaison with dbench on KVM

[Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>]

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Anthony Liguori wrote:
> Laurent Vivier wrote:
>> Hi,
>>
>> I made some benchmarks with dbench on linux/KVM.
>>
>> IDE means I use an image disk with "-hda"
>> SCSI means I use an image disk with "-sda"
>> (see the patch I proposed on qemu list:
>> http://www.mail-archive.com/qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org/msg08679.html )
>>
>> threads KVM-21  KVM-21  KVM-24  KVM-24  KVM-25  KVM-25
>>         IDE     SCSI    IDE     SCSI    IDE     SCSI
>>
>> 1       215.272 94.8775 318.626 319.533 307.111 331.757
>> 2       212.061 91.3193 313.217 315.163 314.577 323.715
>> 4       197.586 81.7551 291.752 276.044 292.084 271.191
>> 8       144.814 58.5725 188.819 198.995 168.273 165.564
>> 16      111.505 66.3605 139.824 157.617 150.822 123.671
>> 32      43.4109 15.7386 48.2109 50.4114 59.1074 69.5717
>> 64      21.0567 8.3535  11.3457 19.9483 20.4877 24.5627
>>
>> 	results are in MB/sec
>>
>> Conclusion:
>>
>> KVM-25 is really better than KVM-21
>> in most cases, SCSI is better than IDE
>>   
> 
> Were you using libposix-aio?  If not, did you change the aio_init 
> function in block-raw.c (assuming that you're using a raw disk).  
> Otherwise, QEMU by default will limit the glibc aio library to a single 
> thread so you won't see a lot of the benefits of SCSI emulation.

Hi Anthony,

I didn't modify aio_init limit...

I made some benchmarks with liposix-aio, but results are worst with IDE and
crashes with SCSI (because I need to make some additional works).

It's the part on which I work now (to align buffers to avoid redundant buffer
copy and open image disk with O_DIRECT).

Regards,
Laurent

-- 
------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org  --------------
       "Any sufficiently advanced technology is
  indistinguishable from magic." - Arthur C. Clarke


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