From: Jangwoong Kim <6812skiii@gmail.com>
To: libc-alpha@sourceware.org
Cc: Jangwoong Kim <6812skiii@gmail.com>
Subject: [PATCH v2] nptl: Effectively skip CAS in spinlock loop
Date: Tue, 14 Dec 2021 20:01:19 +0900 [thread overview]
Message-ID: <20211214110119.592-1-6812skiii@gmail.com> (raw)
The commit:
"Add LLL_MUTEX_READ_LOCK [BZ #28537]"
SHA1: d672a98a1af106bd68deb15576710cd61363f7a6
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.
---
nptl/pthread_mutex_lock.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 47b88a6b5b..3ad199a5e1 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -138,7 +138,7 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
int cnt = 0;
int max_cnt = MIN (max_adaptive_count (),
mutex->__data.__spins * 2 + 10);
- do
+ while (1)
{
if (cnt++ >= max_cnt)
{
@@ -146,10 +146,9 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
break;
}
atomic_spin_nop ();
- if (LLL_MUTEX_READ_LOCK (mutex) != 0)
- continue;
+ if (LLL_MUTEX_READ_LOCK (mutex) == 0 && LLL_MUTEX_TRYLOCK (mutex) == 0)
+ break;
}
- while (LLL_MUTEX_TRYLOCK (mutex) != 0);
mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
}
--
2.25.1
next reply other threads:[~2021-12-14 11:01 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-14 11:01 Jangwoong Kim [this message]
2021-12-14 11:42 ` Andreas Schwab
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