ipc/sem.c: cacheline align the ipc spinlock for semaphores

Cacheline align the spinlock for sysv semaphores.  Without the patch, the
spinlock and sem_otime [written by every semop that modified the array]
and sem_base [read in the hot path of try_atomic_semop()] can be in the
same cacheline.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/sem.h b/include/linux/sem.h
index 8a4adbef8a0fd65b13964b780418b6d7dd84c154..f2961afa2f6657e9bbf9c79cd25b0d2c2648d86d 100644 (file)
--- a/include/linux/sem.h
+++ b/include/linux/sem.h
@@ -79,6 +79,7 @@ struct  seminfo {
 #ifdef __KERNEL__
 #include <asm/atomic.h>
 #include <linux/rcupdate.h>
+#include <linux/cache.h>
 
 struct task_struct;
 
@@ -91,7 +92,8 @@ struct sem {
 
 /* One sem_array data structure for each set of semaphores in the system. */
 struct sem_array {
-       struct kern_ipc_perm    sem_perm;       /* permissions .. see ipc.h */
+       struct kern_ipc_perm    ____cacheline_aligned_in_smp
+                               sem_perm;       /* permissions .. see ipc.h */
        time_t                  sem_otime;      /* last semop time */
        time_t                  sem_ctime;      /* last change time */
        struct sem              *sem_base;      /* ptr to first semaphore in array */