tree 22468665036b37922664529df976c890c5bed2d0
parent 7d6feeb287c61aafa88f06345387b1188edf4b86
author Nick Piggin <npiggin@suse.de> 1260924448 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1260976809 -0800

ipc/sem.c: sem optimise undo list search

Around a month ago, there was some discussion about an improvement of the
sysv sem algorithm: Most (at least: some important) users only use simple
semaphore operations, therefore it's worthwile to optimize this use case.

This patch:

Move last looked up sem_undo struct to the head of the task's undo list.
Attempt to move common entries to the front of the list so search time is
reduced.  This reduces lookup_undo on oprofile of problematic SAP workload
by 30% (see patch 4 for a description of SAP workload).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>