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nptl: Effectively skip CAS in spinlock loop

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The commit:
"Add LLL_MUTEX_READ_LOCK [BZ #28537]"
SHA1: d672a98a1a

introduced LLL_MUTEX_READ_LOCK, to skip CAS in spinlock loop
if atomic load fails. But, "continue" inside of do-while loop
does not skip the evaluation of escape expression, thus CAS
is not skipped.

Replace do-while with while and skip LLL_MUTEX_TRYLOCK if
LLL_MUTEX_READ_LOCK fails.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
This commit is contained in:
Jangwoong Kim 2021-12-14 21:30:51 +09:00 committed by H.J. Lu
parent f44820821a
commit 6b8dbbd03a
1 changed files with 2 additions and 3 deletions
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5
nptl/pthread_mutex_lock.c
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@ -146,10 +146,9 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
break;
}
atomic_spin_nop ();
if (LLL_MUTEX_READ_LOCK (mutex) != 0)
continue;
}
while (LLL_MUTEX_TRYLOCK (mutex) != 0);
while (LLL_MUTEX_READ_LOCK (mutex) != 0
|| LLL_MUTEX_TRYLOCK (mutex) != 0);
mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
}