diff options
Diffstat (limited to 'nptl/pthread_mutex_lock.c')
| -rw-r--r-- | nptl/pthread_mutex_lock.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index d2e652d151..6e767a8724 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -138,14 +138,26 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex) int cnt = 0; int max_cnt = MIN (max_adaptive_count (), mutex->__data.__spins * 2 + 10); + int spin_count, exp_backoff = 1; + unsigned int jitter = get_jitter (); do { - if (cnt++ >= max_cnt) + /* In each loop, spin count is exponential backoff plus + random jitter, random range is [0, exp_backoff-1]. */ + spin_count = exp_backoff + (jitter & (exp_backoff - 1)); + cnt += spin_count; + if (cnt >= max_cnt) { + /* If cnt exceeds max spin count, just go to wait + queue. */ LLL_MUTEX_LOCK (mutex); break; } - atomic_spin_nop (); + do + atomic_spin_nop (); + while (--spin_count > 0); + /* Prepare for next loop. */ + exp_backoff = get_next_backoff (exp_backoff); } while (LLL_MUTEX_READ_LOCK (mutex) != 0 || LLL_MUTEX_TRYLOCK (mutex) != 0); |