Messages in this thread Patch in this message | | | Subject | [PATCH v8 1/9] rwsem: check the lock before cpmxchg in down_write_trylock | From | Tim Chen <> | Date | Wed, 02 Oct 2013 15:38:18 -0700 |
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Cmpxchg will cause the cacheline bouning when do the value checking, that cause scalability issue in a large machine (like a 80 core box).
So a lock pre-read can relief this contention.
Signed-off-by: Alex Shi <alex.shi@intel.com> --- include/asm-generic/rwsem.h | 8 ++++---- 1 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h index bb1e2cd..5ba80e7 100644 --- a/include/asm-generic/rwsem.h +++ b/include/asm-generic/rwsem.h @@ -70,11 +70,11 @@ static inline void __down_write(struct rw_semaphore *sem) static inline int __down_write_trylock(struct rw_semaphore *sem) { - long tmp; + if (unlikely(sem->count != RWSEM_UNLOCKED_VALUE)) + return 0; - tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, - RWSEM_ACTIVE_WRITE_BIAS); - return tmp == RWSEM_UNLOCKED_VALUE; + return cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, + RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_UNLOCKED_VALUE; } /* -- 1.7.4.4
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