Commit-ID: a338ecb07a338c9a8b0ca0010e862ebe598b1551 Gitweb: https://git.kernel.org/tip/a338ecb07a338c9a8b0ca0010e862ebe598b1551 Author: Waiman Long <[email protected]> AuthorDate: Thu, 4 Apr 2019 13:43:13 -0400 Committer: Ingo Molnar <[email protected]> CommitDate: Wed, 10 Apr 2019 10:56:01 +0200
locking/rwsem: Micro-optimize rwsem_try_read_lock_unqueued() The atomic_long_cmpxchg_acquire() in rwsem_try_read_lock_unqueued() is replaced by atomic_long_try_cmpxchg_acquire() to simpify the code and generate slightly better assembly code. There is no functional change. Signed-off-by: Waiman Long <[email protected]> Acked-by: Peter Zijlstra <[email protected]> Acked-by: Will Deacon <[email protected]> Acked-by: Davidlohr Bueso <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Tim Chen <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- kernel/locking/rwsem-xadd.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index c213869e1aa7..f6198e1a58f6 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -259,21 +259,16 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem) */ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem) { - long old, count = atomic_long_read(&sem->count); + long count = atomic_long_read(&sem->count); - while (true) { - if (!(count == 0 || count == RWSEM_WAITING_BIAS)) - return false; - - old = atomic_long_cmpxchg_acquire(&sem->count, count, - count + RWSEM_ACTIVE_WRITE_BIAS); - if (old == count) { + while (!count || count == RWSEM_WAITING_BIAS) { + if (atomic_long_try_cmpxchg_acquire(&sem->count, &count, + count + RWSEM_ACTIVE_WRITE_BIAS)) { rwsem_set_owner(sem); return true; } - - count = old; } + return false; } static inline bool owner_on_cpu(struct task_struct *owner)
