MD Raid 6: poor algorithm choice?

[Chris Boot]

Hi all,

[4295106.360000] raid6: int32x1    714 MB/s
[4295106.381000] raid6: int32x2    742 MB/s
[4295106.403000] raid6: int32x4    632 MB/s
[4295106.429000] raid6: int32x8    523 MB/s
[4295106.453000] raid6: mmxx1     1476 MB/s
[4295106.474000] raid6: mmxx2     2500 MB/s
[4295106.500000] raid6: sse1x1    1375 MB/s
[4295106.521000] raid6: sse1x2    2339 MB/s
[4295106.524000] raid6: using algorithm sse1x2 (2339 MB/s)
[4295106.531000] md: raid6 personality registered for level 6

I just loaded the raid6 module for fun (might end up using it one day), and I 
was surprised at its choice of algorithm. By the messages above, I would have 
assumed it would choose the mmxx2 algorithm at 2500 MB/s instead of sse1x2 at 
the slightly slower 2339 MB/s. This is probably entirely expected behaviour, but 
why?

Cheers,
Chris

--
Chris Boot
bootc@xxxxxxxxx
http://www.bootc.net/
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