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authorManfred Spraul <manfred@colorfullife.com>2017-02-27 14:28:18 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-02-27 18:43:46 -0800
commit9de5ab8a2eeea9ae4b63b6f6353b415b93e020c0 (patch)
treecf33b34f1edcbca39139176cfe1781c41590ca3f /include/linux
parent27d7be1801a4824ecccbc735593101d72c038f13 (diff)
ipc/sem: add hysteresis
sysv sem has two lock modes: One with per-semaphore locks, one lock mode with a single global lock for the whole array. When switching from the per-semaphore locks to the global lock, all per-semaphore locks must be scanned for ongoing operations. The patch adds a hysteresis for switching from the global lock to the per semaphore locks. This reduces how often the per-semaphore locks must be scanned. Compared to the initial patch, this is a simplified solution: Setting USE_GLOBAL_LOCK_HYSTERESIS to 1 restores the current behavior. In theory, a workload with exactly 10 simple sops and then one complex op now scales a bit worse, but this is pure theory: If there is concurrency, the it won't be exactly 10:1:10:1:10:1:... If there is no concurrency, then there is no need for scalability. Link: http://lkml.kernel.org/r/1476851896-3590-3-git-send-email-manfred@colorfullife.com Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: H. Peter Anvin <hpa@zytor.com> Cc: <1vier1@web.de> Cc: kernel test robot <xiaolong.ye@intel.com> Cc: <felixh@informatik.uni-bremen.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/sem.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/sem.h b/include/linux/sem.h
index d0efd6e6c20a..4fc222f8755d 100644
--- a/include/linux/sem.h
+++ b/include/linux/sem.h
@@ -21,7 +21,7 @@ struct sem_array {
struct list_head list_id; /* undo requests on this array */
int sem_nsems; /* no. of semaphores in array */
int complex_count; /* pending complex operations */
- bool complex_mode; /* no parallel simple ops */
+ unsigned int use_global_lock;/* >0: global lock required */
};
#ifdef CONFIG_SYSVIPC