Re: AMD64 and RAID6

[H. Peter Anvin]

Followup to:  <409D1D86.6050907@xxxxxxxxxx>
By author:    "J. Ryan Earl" <heretic@xxxxxxxxxx>
In newsgroup: linux.dev.kernel
>
> I noticed the following in my dmesg:
> 
> raid5: measuring checksumming speed
>   generic_sse:  6604.000 MB/sec
> raid5: using function: generic_sse (6604.000 MB/sec)
> raid6: int64x1   1847 MB/s
> raid6: int64x2   2753 MB/s
> raid6: int64x4   2878 MB/s
> raid6: int64x8   1902 MB/s
> raid6: sse2x1    1015 MB/s
> raid6: sse2x2    1488 MB/s
> raid6: sse2x4    1867 MB/s
> raid6: using algorithm sse2x4 (1867 MB/s)
> md: raid6 personality registered as nr 8
> md: md driver 0.90.0 MAX_MD_DEVS=256, MD_SB_DISKS=27
> 
> Why doesn't RAID6 use the int64x4 algorithm in this situation?  What is 
> the motivation of setting the 'prefer field' on the sse algorithms and 
> not on the integer based algorithms?
> 

The SSE algorithms are non-cache-polluting.  This makes them slightly
slower, but avoids slowing the rest of the machine down as much.

	-hpa
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