From: "H.J. Lu" <hjl.tools@gmail.com>
To: libc-alpha@sourceware.org
Cc: Florian Weimer <fweimer@redhat.com>,
Oleh Derevenko <oleh.derevenko@gmail.com>,
Arjan van de Ven <arjan@linux.intel.com>,
Andreas Schwab <schwab@linux-m68k.org>,
"Paul A . Clarke" <pc@us.ibm.com>,
Noah Goldstein <goldstein.w.n@gmail.com>
Subject: [PATCH v6 1/4] Add LLL_MUTEX_READ_LOCK [BZ #28537]
Date: Thu, 11 Nov 2021 08:24:25 -0800 [thread overview]
Message-ID: <20211111162428.2286605-2-hjl.tools@gmail.com> (raw)
In-Reply-To: <20211111162428.2286605-1-hjl.tools@gmail.com>
CAS instruction is expensive. From the x86 CPU's point of view, getting
a cache line for writing is more expensive than reading. See Appendix
A.2 Spinlock in:
https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/xeon-lock-scaling-analysis-paper.pdf
The full compare and swap will grab the cache line exclusive and cause
excessive cache line bouncing.
Add LLL_MUTEX_READ_LOCK to do an atomic load and skip CAS in spinlock
loop if compare may fail to reduce cache line bouncing on contended locks.
---
nptl/pthread_mutex_lock.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 2bd41767e0..72058c719c 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -64,6 +64,11 @@ lll_mutex_lock_optimized (pthread_mutex_t *mutex)
# define PTHREAD_MUTEX_VERSIONS 1
#endif
+#ifndef LLL_MUTEX_READ_LOCK
+# define LLL_MUTEX_READ_LOCK(mutex) \
+ atomic_load_relaxed (&(mutex)->__data.__lock)
+#endif
+
static int __pthread_mutex_lock_full (pthread_mutex_t *mutex)
__attribute_noinline__;
@@ -141,6 +146,8 @@ 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);
--
2.33.1
next prev parent reply other threads:[~2021-11-11 16:24 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 16:24 [PATCH v6 0/4] Optimize CAS " H.J. Lu
2021-11-11 16:24 ` H.J. Lu [this message]
2021-11-12 17:23 ` [PATCH v6 1/4] Add LLL_MUTEX_READ_LOCK " Szabolcs Nagy
2021-11-17 2:24 ` Noah Goldstein
2021-11-17 23:54 ` H.J. Lu
2021-11-18 0:03 ` Noah Goldstein
2021-11-18 0:31 ` H.J. Lu
2021-11-18 1:16 ` Arjan van de Ven
2022-09-11 20:19 ` Sunil Pandey
2022-09-29 0:10 ` Noah Goldstein
2021-11-11 16:24 ` [PATCH v6 2/4] Avoid extra load with CAS in __pthread_mutex_lock_full " H.J. Lu
2021-11-12 16:31 ` Szabolcs Nagy
2021-11-12 18:50 ` Andreas Schwab
2022-09-11 20:16 ` Sunil Pandey
2022-09-29 0:10 ` Noah Goldstein
2021-11-11 16:24 ` [PATCH v6 3/4] Reduce CAS in malloc spinlocks H.J. Lu
2023-02-23 5:48 ` DJ Delorie
2021-11-11 16:24 ` [PATCH v6 4/4] Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537] H.J. Lu
2021-11-12 16:32 ` Szabolcs Nagy
2021-11-12 18:51 ` Andreas Schwab
2022-09-11 20:12 ` Sunil Pandey
2022-09-11 20:15 ` Arjan van de Ven
2022-09-11 21:26 ` Florian Weimer
2022-09-29 0:09 ` Noah Goldstein
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