iozone regression with 2.6.29-rc6

Lin Ming
2009-02-27T09:18:09Z

bisect locates below commits,

commit 1cf6e7d83bf334cc5916137862c920a97aabc018
Author: Nick Piggin <npiggin@suse.de>
Date: Wed Feb 18 14:48:18 2009 -0800

mm: task dirty accounting fix

YAMAMOTO-san noticed that task_dirty_inc doesn't seem to be called properly for
cases where set_page_dirty is not used to dirty a page (eg. mark_buffer_dirty).

Additionally, there is some inconsistency about when task_dirty_inc is
called. It is used for dirty balancing, however it even gets called for
__set_page_dirty_no_writeback.

So rather than increment it in a set_page_dirty wrapper, move it down to
exactly where the dirty page accounting stats are incremented.

Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

below data in parenthesis is the result after above commit reverted, for example,
-10% (+2%) means,
iozone has ~10% regression with 2.6.29-rc6 compared with 2.6.29-rc5.
and
iozone has ~2% improvement with 2.6.29-rc6-revert-1cf6e7d compared with 2.6.29-rc5.

4P dual-core HT 2P qual-core 2P qual-core HT
tulsa stockley Nehalem
--------------------------------------------------------
iozone-rewrite -10% (+2%) -8% (0%) -10% (-7%)
iozone-rand-write -50% (0%) -20% (+10%)
iozone-read -13% (0%)
iozone-write -28% (-1%)
iozone-reread -5% (-1%)
iozone-mmap-read -7% (+2%)
iozone-mmap-reread -7% (+2%)
iozone-mmap-rand-read -7% (+3%)
iozone-mmap-rand-write -5% (0%)

Lin Ming