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* [PATCH] Move assignment out of the CAS condition
@ 2021-11-12 20:22 H.J. Lu
  2021-11-15 13:42 ` Andreas Schwab
  0 siblings, 1 reply; 4+ messages in thread
From: H.J. Lu @ 2021-11-12 20:22 UTC (permalink / raw)
  To: libc-alpha; +Cc: Szabolcs Nagy, Andreas Schwab

Update

commit 49302b8fdf9103b6fc0a398678668a22fa19574c
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:54:01 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

and

commit 0b82747dc48d5bf0871bdc6da8cb6eec1256355f
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:31:51 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

by moving assignment out of the CAS condition.
---
 nptl/pthread_mutex_lock.c      | 7 +++----
 nptl/pthread_mutex_timedlock.c | 7 +++----
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 762059b230..47b88a6b5b 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -304,10 +304,9 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index f763cfc7fa..791a2b54b1 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -233,10 +233,9 @@ __pthread_mutex_clocklock_common (pthread_mutex_t *mutex,
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;
-- 
2.33.1


^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2022-09-29  0:09 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-11-12 20:22 [PATCH] Move assignment out of the CAS condition H.J. Lu
2021-11-15 13:42 ` Andreas Schwab
2022-09-11 20:21   ` Sunil Pandey
2022-09-29  0:09     ` Noah Goldstein

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