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

[Sunil K Pandey]

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

Tested on x86_64.

Fixes BZ #33704.
---
 nptl/pthread_mutex_trylock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/nptl/pthread_mutex_trylock.c b/nptl/pthread_mutex_trylock.c
index 94621cc254..e3f83311c1 100644
--- a/nptl/pthread_mutex_trylock.c
+++ b/nptl/pthread_mutex_trylock.c
@@ -60,7 +60,10 @@ ___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;
 
       /* Record the ownership.  */
-- 
2.51.0