Re: AMD64 and RAID6

From: H. Peter Anvin
Date: Mon May 10 2004 - 21:15:45 EST

Followup to: <409D1D86.6050907@xxxxxxxxxx>
By author: "J. Ryan Earl" <heretic@xxxxxxxxxx>
In newsgroup:
> 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.

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