lkml.org 
[lkml]   [2019]   [Feb]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH-tip v2 04/10] locking/rwsem: Micro-optimize rwsem_try_read_lock_unqueued()
Date
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>
---
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
\
 
 \ /
  Last update: 2019-02-15 21:51    [W:0.104 / U:28.928 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site