diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index dd26bf6dee0c1aec58a6d3684d05ae50aadc613b..4bd95465af55fec305add8bf896b67f1222dbf8f 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -46,12 +46,6 @@ # include #endif -/* - * A negative mutex count indicates that waiters are sleeping waiting for the - * mutex. - */ -#define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) >= 0) - void __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) { @@ -483,8 +477,11 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, #endif spin_lock_mutex(&lock->wait_lock, flags); - /* once more, can we acquire the lock? */ - if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, 0) == 1)) + /* + * Once more, try to acquire the lock. Only try-lock the mutex if + * lock->count >= 0 to reduce unnecessary xchg operations. + */ + if (atomic_read(&lock->count) >= 0 && (atomic_xchg(&lock->count, 0) == 1)) goto skip_wait; debug_mutex_lock_common(lock, &waiter); @@ -504,9 +501,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, * it's unlocked. Later on, if we sleep, this is the * operation that gives us the lock. We xchg it to -1, so * that when we release the lock, we properly wake up the - * other waiters: + * other waiters. We only attempt the xchg if the count is + * non-negative in order to avoid unnecessary xchg operations: */ - if (MUTEX_SHOW_NO_WAITER(lock) && + if (atomic_read(&lock->count) >= 0 && (atomic_xchg(&lock->count, -1) == 1)) break;