diff options
Diffstat (limited to 'include/linux/rwsem.h')
| -rw-r--r-- | include/linux/rwsem.h | 37 |
1 files changed, 16 insertions, 21 deletions
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 67dbb57508b1..2ea18a3def04 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -20,25 +20,30 @@ #include <linux/osq_lock.h> #endif -struct rw_semaphore; - -#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK -#include <linux/rwsem-spinlock.h> /* use a generic implementation */ -#define __RWSEM_INIT_COUNT(name) .count = RWSEM_UNLOCKED_VALUE -#else -/* All arch specific implementations share the same struct */ +/* + * For an uncontended rwsem, count and owner are the only fields a task + * needs to touch when acquiring the rwsem. So they are put next to each + * other to increase the chance that they will share the same cacheline. + * + * In a contended rwsem, the owner is likely the most frequently accessed + * field in the structure as the optimistic waiter that holds the osq lock + * will spin on owner. For an embedded rwsem, other hot fields in the + * containing structure should be moved further away from the rwsem to + * reduce the chance that they will share the same cacheline causing + * cacheline bouncing problem. + */ struct rw_semaphore { atomic_long_t count; - struct list_head wait_list; - raw_spinlock_t wait_lock; #ifdef CONFIG_RWSEM_SPIN_ON_OWNER - struct optimistic_spin_queue osq; /* spinner MCS lock */ /* * Write owner. Used as a speculative check to see * if the owner is running on the cpu. */ struct task_struct *owner; + struct optimistic_spin_queue osq; /* spinner MCS lock */ #endif + raw_spinlock_t wait_lock; + struct list_head wait_list; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif @@ -50,24 +55,14 @@ struct rw_semaphore { */ #define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-2L) -extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); -extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem); -extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); -extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem); -extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); -extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); - -/* Include the arch specific part */ -#include <asm/rwsem.h> - /* In all implementations count != 0 means locked */ static inline int rwsem_is_locked(struct rw_semaphore *sem) { return atomic_long_read(&sem->count) != 0; } +#define RWSEM_UNLOCKED_VALUE 0L #define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) -#endif /* Common initializer macros and functions */ |