[v5,3/3] Optimize CAS in __pthread_mutex_lock_full [BZ #28537]
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Context |
Check |
Description |
dj/TryBot-apply_patch |
success
|
Patch applied to master at the time it was sent
|
dj/TryBot-32bit |
success
|
Build for i686
|
Commit Message
1. Do an atomic load and skip CAS if compare may fail to reduce cache
line bouncing on contended locks.
2. Replace atomic_compare_and_exchange_bool_acq with
atomic_compare_and_exchange_val_acq to avoid the extra load.
---
nptl/pthread_mutex_lock.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
@@ -297,12 +297,13 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
meantime. */
if ((oldval & FUTEX_WAITERS) == 0)
{
- if (atomic_compare_and_exchange_bool_acq (&mutex->__data.__lock,
- oldval | FUTEX_WAITERS,
- oldval)
- != 0)
+ int val = atomic_load_relaxed (&mutex->__data.__lock);
+ if (val != oldval
+ || ((val = atomic_compare_and_exchange_val_acq
+ (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
+ oldval)) != oldval))
{
- oldval = mutex->__data.__lock;
+ oldval = val;
continue;
}
oldval |= FUTEX_WAITERS;