Re: Performance comparaison with dbench on KVM

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

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.

Regards,

Anthony Liguori

> Cheers,
> Laurent
>   
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