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From: Sunil Pandey <skpgkp2@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/release/2.33/master] Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537] Date: Thu, 29 Sep 2022 00:47:53 +0000 (GMT) [thread overview] Message-ID: <20220929004753.E58BD3858D28@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=f5a70409db67f3a5f035d9d6082d11efcc74910d commit f5a70409db67f3a5f035d9d6082d11efcc74910d 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. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com> (cherry picked from commit 0b82747dc48d5bf0871bdc6da8cb6eec1256355f) Diff: --- nptl/pthread_mutex_lock.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 319658adc4..0fd7467b97 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -289,12 +289,12 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex) meantime. */ if ((oldval & FUTEX_WAITERS) == 0) { - if (atomic_compare_and_exchange_bool_acq (&mutex->__data.__lock, - oldval | FUTEX_WAITERS, - oldval) - != 0) + int val; + if ((val = atomic_compare_and_exchange_val_acq + (&mutex->__data.__lock, oldval | FUTEX_WAITERS, + oldval)) != oldval) { - oldval = mutex->__data.__lock; + oldval = val; continue; } oldval |= FUTEX_WAITERS;
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