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

[Avi Kivity]

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.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.