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authorManfred Spraul <manfred@colorfullife.com>2009-12-15 16:47:33 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-16 07:20:10 -0800
commit636c6be823870d829b37fc96655bb8820a6a9be9 (patch)
treedc17d73ae77e6921ca7c88e6b019fe3d72bb9790 /ipc
parentb97e820ffffbf49e94ed60c9c26f1a54bccae924 (diff)
downloadkernel-636c6be823870d829b37fc96655bb8820a6a9be9.tar.gz
ipc/sem.c: optimize single semop operations
sysv sem has the concept of semaphore arrays that consist out of multiple semaphores. Atomic operations that affect multiple semaphores are supported. The patch optimizes single semaphore operation calls that affect only one semaphore: It's not necessary to scan all pending operations, it is sufficient to scan the per-semaphore list. The idea is from Nick Piggin version of an ipc sem improvement, the implementation is different: The code tries to keep as much common code as possible. As the result, the patch is simpler, but optimizes fewer cases. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Nick Piggin <npiggin@suse.de> 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.c51
1 files changed, 40 insertions, 11 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index 4252a8eb77e2..7eb6f049dd7c 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -434,17 +434,45 @@ static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
sma->complex_count--;
}
-/* Go through the pending queue for the indicated semaphore
- * looking for tasks that can be completed.
+
+/**
+ * update_queue(sma, semnum): Look for tasks that can be completed.
+ * @sma: semaphore array.
+ * @semnum: semaphore that was modified.
+ *
+ * update_queue must be called after a semaphore in a semaphore array
+ * was modified. If multiple semaphore were modified, then @semnum
+ * must be set to -1.
*/
-static void update_queue (struct sem_array * sma)
+static void update_queue(struct sem_array *sma, int semnum)
{
- struct sem_queue *q, *tq;
+ struct sem_queue *q;
+ struct list_head *walk;
+ struct list_head *pending_list;
+ int offset;
+
+ /* if there are complex operations around, then knowing the semaphore
+ * that was modified doesn't help us. Assume that multiple semaphores
+ * were modified.
+ */
+ if (sma->complex_count)
+ semnum = -1;
+
+ if (semnum == -1) {
+ pending_list = &sma->sem_pending;
+ offset = offsetof(struct sem_queue, list);
+ } else {
+ pending_list = &sma->sem_base[semnum].sem_pending;
+ offset = offsetof(struct sem_queue, simple_list);
+ }
again:
- list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {
- int error;
- int alter;
+ walk = pending_list->next;
+ while (walk != pending_list) {
+ int error, alter;
+
+ q = (struct sem_queue *)((char *)walk - offset);
+ walk = walk->next;
error = try_atomic_semop(sma, q->sops, q->nsops,
q->undo, q->pid);
@@ -769,7 +797,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma);
+ update_queue(sma, -1);
err = 0;
goto out_unlock;
}
@@ -811,7 +839,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
curr->sempid = task_tgid_vnr(current);
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma);
+ update_queue(sma, semnum);
err = 0;
goto out_unlock;
}
@@ -1187,7 +1215,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
error = try_atomic_semop (sma, sops, nsops, un, task_tgid_vnr(current));
if (error <= 0) {
if (alter && error == 0)
- update_queue (sma);
+ update_queue(sma, (nsops == 1) ? sops[0].sem_num : -1);
+
goto out_unlock_free;
}
@@ -1388,7 +1417,7 @@ void exit_sem(struct task_struct *tsk)
}
sma->sem_otime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma);
+ update_queue(sma, -1);
sem_unlock(sma);
call_rcu(&un->rcu, free_un);