Subject: + ipc-semc-optimize-sem_lock.patch added to -mm tree
To: manfred@xxxxxxxxxxxxxxxx,bitbucket@xxxxxxxxx,davidlohr@xxxxxx,riel@xxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Mon, 23 Sep 2013 14:07:44 -0700
The patch titled
Subject: ipc/sem.c: optimize sem_lock()
has been added to the -mm tree. Its filename is
ipc-semc-optimize-sem_lock.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-semc-optimize-sem_lock.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-semc-optimize-sem_lock.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
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 <manfred@xxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <bitbucket@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Reviewed-by: Davidlohr Bueso <davidlohr@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff -puN ipc/sem.c~ipc-semc-optimize-sem_lock ipc/sem.c
--- a/ipc/sem.c~ipc-semc-optimize-sem_lock
+++ a/ipc/sem.c
@@ -248,12 +248,20 @@ static void merge_queues(struct sem_arra
* 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);
_
Patches currently in -mm which might be from manfred@xxxxxxxxxxxxxxxx are
ipc-semc-fix-race-in-sem_lock.patch
ipc-semc-optimize-sem_lock.patch
slab-leaks3-default-y.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
