Commit b6e90822 authored Dec 15, 2009 by Manfred Spraul Committed by Linus Torvalds Dec 16, 2009

ipc/sem.c: optimize if semops fail



Reduce the amount of scanning of the list of pending semaphore operations:
If try_atomic_semop failed, then no changes were applied.  Thus no need to
restart.

Additionally, this patch correct an incorrect comment: It's possible to
wait for arbitrary semaphore values (do a dec by <x>, wait-for-zero, inc
by <x> in one atomic operation)

Both changes are from Nick Piggin, the patch is the result of a different
split of the individual changes.

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>

parent d4212093

ipc/sem.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -445,13 +445,13 @@ static void update_queue (struct sem_array * sma)
		* of the completed operation:
		* - if the operation modified the array, then restart from the
		* head of the queue and check for threads that might be
		* waiting for semaphore values to become 0.
		* waiting for the new semaphore values.
		* - if the operation didn't modify the array, then just
		* continue.
		*/
		alter = q->alter;
		wake_up_sem_queue(q, error);
		if (alter)
		if (alter && !error)
		goto again;
		}
		}