From: "H.J. Lu" <hjl.tools@gmail.com>
To: libc-alpha@sourceware.org
Cc: Szabolcs Nagy <szabolcs.nagy@arm.com>,
Andreas Schwab <schwab@linux-m68k.org>
Subject: [PATCH] Move assignment out of the CAS condition
Date: Fri, 12 Nov 2021 12:22:56 -0800 [thread overview]
Message-ID: <20211112202256.1591340-1-hjl.tools@gmail.com> (raw)
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
next reply other threads:[~2021-11-12 20:23 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-12 20:22 H.J. Lu [this message]
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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