Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH-tip v3 04/11] locking/rwsem: Micro-optimize rwsem_try_read_lock_unqueued() | Date | Thu, 28 Feb 2019 14:09:34 -0500 |
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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 <longman@redhat.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Davidlohr Bueso <dbueso@suse.de> --- 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 c213869..f6198e1 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) -- 1.8.3.1
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