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46 lines
1.6 KiB
46 lines
1.6 KiB
commit a6b81f605dfba8650ea1f80122f41eb8e6c73dc7 |
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Author: H.J. Lu <hjl.tools@gmail.com> |
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Date: Tue Nov 2 18:33:07 2021 -0700 |
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Add LLL_MUTEX_READ_LOCK [BZ #28537] |
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CAS instruction is expensive. From the x86 CPU's point of view, getting |
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a cache line for writing is more expensive than reading. See Appendix |
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A.2 Spinlock in: |
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https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/xeon-lock-scaling-analysis-paper.pdf |
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The full compare and swap will grab the cache line exclusive and cause |
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excessive cache line bouncing. |
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Add LLL_MUTEX_READ_LOCK to do an atomic load and skip CAS in spinlock |
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loop if compare may fail to reduce cache line bouncing on contended locks. |
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Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com> |
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(cherry picked from commit d672a98a1af106bd68deb15576710cd61363f7a6) |
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diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c |
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index a04e0158451c8fff..9f40928cc6b9a067 100644 |
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--- a/nptl/pthread_mutex_lock.c |
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+++ b/nptl/pthread_mutex_lock.c |
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@@ -65,6 +65,11 @@ lll_mutex_lock_optimized (pthread_mutex_t *mutex) |
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# define PTHREAD_MUTEX_VERSIONS 1 |
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#endif |
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+#ifndef LLL_MUTEX_READ_LOCK |
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+# define LLL_MUTEX_READ_LOCK(mutex) \ |
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+ atomic_load_relaxed (&(mutex)->__data.__lock) |
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+#endif |
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+ |
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static int __pthread_mutex_lock_full (pthread_mutex_t *mutex) |
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__attribute_noinline__; |
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@@ -142,6 +147,8 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex) |
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break; |
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} |
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atomic_spin_nop (); |
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+ if (LLL_MUTEX_READ_LOCK (mutex) != 0) |
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+ continue; |
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} |
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while (LLL_MUTEX_TRYLOCK (mutex) != 0); |
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