From bf17bb717759d50a2733a7a8157a7c4a25d93abc Mon Sep 17 00:00:00 2001 From: Nick Piggin 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 Signed-off-by: Manfred Spraul Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/sem.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/ipc/sem.c b/ipc/sem.c index 2f2a47959576..cb0070ecf5bf 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -962,17 +962,31 @@ static inline int get_undo_list(struct sem_undo_list **undo_listp) return 0; } -static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid) +static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid) { - struct sem_undo *walk; + struct sem_undo *un; - list_for_each_entry_rcu(walk, &ulp->list_proc, list_proc) { - if (walk->semid == semid) - return walk; + list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) { + if (un->semid == semid) + return un; } return NULL; } +static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid) +{ + struct sem_undo *un; + + assert_spin_locked(&ulp->lock); + + un = __lookup_undo(ulp, semid); + if (un) { + list_del_rcu(&un->list_proc); + list_add_rcu(&un->list_proc, &ulp->list_proc); + } + return un; +} + /** * find_alloc_undo - Lookup (and if not present create) undo array * @ns: namespace @@ -1308,7 +1322,7 @@ void exit_sem(struct task_struct *tsk) if (IS_ERR(sma)) continue; - un = lookup_undo(ulp, semid); + un = __lookup_undo(ulp, semid); if (un == NULL) { /* exit_sem raced with IPC_RMID+semget() that created * exactly the same semid. Nothing to do. -- 2.20.1