linux/ipc
Manfred Spraul d987f8b213 ipc/sem.c: optimize single sops when semval is zero
If multiple simple decrements on the same semaphore are pending, then the
current code scans all decrement operations, even if the semaphore value
is already 0.

The patch optimizes that: if the semaphore value is 0, then there is no
need to scan the q->alter entries.

Note that this is a common case: It happens if 100 decrements by one are
pending and now an increment by one increases the semaphore value from 0
to 1.  Without this patch, all 100 entries are scanned.  With the patch,
only one entry is scanned, then woken up.  Then the new rule triggers and
the scanning is aborted, without looking at the remaining 99 tasks.

With this patch, single sop increment/decrement by 1 are now O(1).
(same as with Nick's patch)

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>
2009-12-16 07:20:10 -08:00
..
compat_mq.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
compat.c fix logic error in ipc compat semctl() 2007-07-06 10:23:43 -07:00
ipc_sysctl.c sysctl ipc: Remove dead binary sysctl support code. 2009-11-12 02:04:54 -08:00
ipcns_notifier.c ipc: do not use a negative value to re-enable msgmni automatic recomputing 2008-07-25 10:53:42 -07:00
Makefile namespaces: mqueue namespace: adapt sysctl 2009-04-07 08:31:09 -07:00
mq_sysctl.c sysctl ipc: Remove dead binary sysctl support code. 2009-11-12 02:04:54 -08:00
mqueue.c const: mark remaining super_operations const 2009-09-22 07:17:24 -07:00
msg.c ipc ns: fix memory leak (idr) 2009-12-16 07:20:09 -08:00
msgutil.c namespaces: ipc namespaces: implement support for posix msqueues 2009-04-07 08:31:09 -07:00
namespace.c ipcns: make free_ipc_ns() static 2009-06-18 13:03:56 -07:00
sem.c ipc/sem.c: optimize single sops when semval is zero 2009-12-16 07:20:10 -08:00
shm.c ipc ns: fix memory leak (idr) 2009-12-16 07:20:09 -08:00
util.c seq_file: constify seq_operations 2009-09-23 07:39:29 -07:00
util.h ipc: unbreak 32-bit shmctl/semctl/msgctl 2009-06-21 12:48:43 -07:00