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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>
This commit is contained in:
Manfred Spraul 2009-12-15 16:47:31 -08:00 committed by Linus Torvalds
parent d4212093dc
commit b6e90822e7
1 changed files with 2 additions and 2 deletions
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4
ipc/sem.c
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@ -445,13 +445,13 @@ again:
* 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;
}
}