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| author | Nick Piggin <npiggin@suse.de> | 2009-12-15 16:47:28 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-12-16 07:20:09 -0800 |
| commit | bf17bb717759d50a2733a7a8157a7c4a25d93abc (patch) | |
| tree | 22468665036b37922664529df976c890c5bed2d0 /ipc | |
| parent | 7d6feeb287c61aafa88f06345387b1188edf4b86 (diff) | |
| download | lwn-bf17bb717759d50a2733a7a8157a7c4a25d93abc.tar.gz lwn-bf17bb717759d50a2733a7a8157a7c4a25d93abc.zip | |
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>
Diffstat (limited to 'ipc')
| -rw-r--r-- | ipc/sem.c | 26 |
1 files 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. |