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From: Manfred Spraul on 18 Apr 2010 13:10
This patch cacheline aligns 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.
---
include/linux/sem.h | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/include/linux/sem.h b/include/linux/sem.h
index 8a4adbe..f2961af 100644
--- 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 */
--
1.6.6.1

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Prev: [PATCH] uml: Fix build breakage after slab.h changes
Next: uml: pthreads instead of manual clone()?