From bf17bb717759d50a2733a7a8157a7c4a25d93abc Mon Sep 17 00:00:00 2001
From: Nick Piggin <npiggin@suse.de>
Date: Tue, 15 Dec 2009 16:47:28 -0800
Subject: [PATCH] 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>
---
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