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

[Laurent Vivier]

Le vendredi 17 octobre 2008 à 14:48 +0200, Avi Kivity a écrit :
> Anthony Liguori wrote:
> >>
> >>                  | 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.
> 
> I don't know mysql well, but perhaps it sizes its internal cache to
> system memory size, so baremetal has 4x the amount of cache.
> 
> If mysql uses mmap to access its data files, then it automatically
> scales with system memory.

It is what I thought but no: I've approximately the same results with
"mem=512M".

Regards,
Laurent
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