fio rand read/write regression with 2.6.32-rc3

[Zhang, Yanmin]

Comparing with 2.6.23-rc1's result, fio rand read write has regression
on my 2*4 core stoakley machine (8GB memory) with a JBOD of 12 disks.

Every disk has 8 1-GB files. Start 8 sub-processes per disk and every
process random chooses a file on the disk to do 36 times of file read or
write on the file and then choose another file.


fio_mmap_rand_read_4k regresion is about 35%.
Bisect down to patch:
1d2235152dc745c6d94bedb550fea84cffdbf768 is first bad commit
commit 1d2235152dc745c6d94bedb550fea84cffdbf768
Author: Jens Axboe <jens.axboe@xxxxxxxxxx>
Date:   Fri Oct 2 19:27:04 2009 +0200

    cfq-iosched: add a knob for desktop interactiveness


After I revert the patch against 2.6.23-rc3, fio_mmap_rand_read_4k regression
disappears.

fio_mmap_randrw_4k has less than 20% regression and reverting the patch
could restore performance.

On another stoakley machine with another JBOD, we see the similiar regression.

ffsb rand read/write has a bigger regression and reverting the patch
could restore performance.

Yanmin


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