Re: [Qemu-devel] Re: [RFC] Disk integrity in QEMU

[Anthony Liguori]

Laurent Vivier wrote:
> Hi,
>
> I've made a benchmark using a database:
> mysql and sysbench in OLTP mode.
>
> cache=off seems to be the best choice in this case...
>   

It would be interesting for you to run the same workload under KVM.

> mysql database
> http://sysbench.sourceforge.net
>
> sysbench --test=oltp
>
> 200,000 requests on 2,000,000 rows table.
>
>                  | total time | per-request stat (ms) |
>                  |  (seconds) |  min  |  avg  |  max  |
> -----------------+------------+-------+-------+-------+
> baremetal        |   208.6237 |   2.5 |  16.7 | 942.6 |
> -----------------+------------+-------+-------+-------+
> cache=on         |   642.2962 |   2.5 |  51.4 | 326.9 |
> -----------------+------------+-------+-------+-------+
> cache=on,O_DSYNC |   646.6570 |   2.7 |  51.7 | 347.0 |
> -----------------+------------+-------+-------+-------+
> cache=off        |   635.4424 |   2.9 |  50.8 | 399.5 |
> -----------------+------------+-------+-------+-------+
>   

Because you're talking about 1/3% of native performance.  This means 
that you may be dominated by things like CPU overhead verses actual IO 
throughput.

Regards,

Anthony Liguori

> Laurent
>