linux-kernel - 2.6.33.1: RAID multi-core processing experimental option is broken.

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Date:	Wed, 24 Mar 2010 07:50:19 -0400 (EDT)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	linux-raid@...r.kernel.org
cc:	linux-kernel@...r.kernel.org
Subject: 2.6.33.1: RAID multi-core processing experimental option is
 broken.

Hi,

2.6.33.1/x86_64 on an e6700 processor:

If you accidentally check [*] for Multi-core processing, the speed is
about 5MiB/s and there are some 254 processes.

When its not enabled, the speed goes back to normal and there are no longer
200-300 processes running, I have reproduced this on multiple machines now.

Enable this option in the kernel, boot the new kernel, do some raid i/o
operations/or a check/resync to the array and it will be 1/4 the speed when
multi-core processing is enabled.
   | |    [ ]       RAID-4/RAID-5/RAID-6 Multicore processing (EXPERIMENTAL| |

With it disabled, we're good:
md0 : active raid6 sdg1[5] sde1[3] sdf1[4] sdd1[2] sdc1[1] sdb1[0]
       1562834944 blocks level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
       [========>............]  resync = 44.5% (173910976/390708736) finish=178.3min speed=20253K/sec

Justin.

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