From: Sunil K Pandey <sunil.k.pandey@intel.com>
Date: Tue, 9 Dec 2025 16:57:44 +0000 (-0800)
Subject: nptl: Optimize trylock for high cache contention workloads (BZ #33704)
X-Git-Tag: glibc-2.43~78
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=63716823dbad9482e09972907ae98e9cb00f9b86;p=thirdparty%2Fglibc.git

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

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.

Co-authored-by: Alex M Wells <alex.m.wells@intel.com>
Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
---

diff --git a/nptl/pthread_mutex_trylock.c b/nptl/pthread_mutex_trylock.c
index 94621cc254..fe9ba8da67 100644
--- a/nptl/pthread_mutex_trylock.c
+++ b/nptl/pthread_mutex_trylock.c
@@ -47,7 +47,8 @@ ___pthread_mutex_trylock (pthread_mutex_t *mutex)
 	  return 0;
 	}
 
-      if (lll_trylock (mutex->__data.__lock) == 0)
+      if (atomic_load_relaxed (&(mutex->__data.__lock)) == 0
+	  && lll_trylock (mutex->__data.__lock) == 0)
 	{
 	  /* 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;
 
       /* Record the ownership.  */