[PATCH v3] nptl: Optimize trylock for high cache contention workloads (BZ #33704)

[Wilco Dijkstra]

Hi Sunil,

> Check lock availability before acquisition to reduce cache line
> bouncing.  Significantly improves trylock throughput on multi-core
> systems under heavy contention.

LGTM.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

Cheers,
Wilco


-      if (lll_trylock (mutex->__data.__lock) == 0)
+      if (atomic_load_relaxed (&(mutex->__data.__lock)) == 0
+	  && lll_trylock (mutex->__data.__lock) == 0)

OK
 	{
 	  /* Record the ownership.  */
 	  mutex->__data.__owner = id;
@@ -60,7 +61,10 @@ ___pthread_mutex_trylock (pthread_mutex_t *mutex)
     case PTHREAD_MUTEX_TIMED_NP:
     case PTHREAD_MUTEX_ADAPTIVE_NP:
     case PTHREAD_MUTEX_ERRORCHECK_NP:
-      if (lll_trylock (mutex->__data.__lock) != 0)
+      /* Mutex type is already loaded, lock check overhead should
+         be minimal.  */
+      if (atomic_load_relaxed (&(mutex->__data.__lock)) != 0
+	  || lll_trylock (mutex->__data.__lock) != 0)
 	break;

OK