From 6d07b68ce16ae9535955ba2059dedba5309c3ca1 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Mon, 30 Sep 2013 13:45:06 -0700 Subject: ipc/sem.c: optimize sem_lock() Operations that need access to the whole array must guarantee that there are no simple operations ongoing. Right now this is achieved by spin_unlock_wait(sem->lock) on all semaphores. If complex_count is nonzero, then this spin_unlock_wait() is not necessary, because it was already performed in the past by the thread that increased complex_count and even though sem_perm.lock was dropped inbetween, no simple operation could have started, because simple operations cannot start when complex_count is non-zero. Signed-off-by: Manfred Spraul Cc: Mike Galbraith Cc: Rik van Riel Reviewed-by: Davidlohr Bueso Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/sem.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/ipc/sem.c b/ipc/sem.c index 4a92c0447ad6..e20658d76bb5 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -257,12 +257,20 @@ static void sem_rcu_free(struct rcu_head *head) * Caller must own sem_perm.lock. * New simple ops cannot start, because simple ops first check * that sem_perm.lock is free. + * that a) sem_perm.lock is free and b) complex_count is 0. */ static void sem_wait_array(struct sem_array *sma) { int i; struct sem *sem; + if (sma->complex_count) { + /* The thread that increased sma->complex_count waited on + * all sem->lock locks. Thus we don't need to wait again. + */ + return; + } + for (i = 0; i < sma->sem_nsems; i++) { sem = sma->sem_base + i; spin_unlock_wait(&sem->lock); -- cgit v1.2.3