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[Qemu-devel] [PATCH] atomic: using memory_order_relaxed for refcnt inc/d
From: |
Liu Ping Fan |
Subject: |
[Qemu-devel] [PATCH] atomic: using memory_order_relaxed for refcnt inc/dec ops |
Date: |
Fri, 12 Jul 2013 14:32:51 +0800 |
Refcnt's atomic inc/dec ops are frequent and its idiom need no seq_cst
order. So to get better performance, it worth to adopt _relaxed
other than _seq_cst memory model on them.
We resort to gcc builtins. If gcc supports C11 memory model, __atomic_*
buitlins is used, otherwise __sync_* builtins.
Signed-off-by: Liu Ping Fan <address@hidden>
---
include/qemu/atomic.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index 0aa8913..1f474b7 100644
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -183,8 +183,15 @@
#endif
/* Provide shorter names for GCC atomic builtins. */
+#ifndef _GLIBCXX_ATOMIC_BUILTINS
+/* close to C11 memory_order_seq_cst */
#define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1)
#define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1)
+#else
+/* C11 memory_order_relaxed */
+#define atomic_fetch_inc(ptr) __atomic_fetch_add(ptr, 1, __ATOMIC_RELAXED)
+#define atomic_fetch_dec(ptr) __atomic_fetch_add(ptr, -1, __ATOMIC_RELAXED)
+#endif
#define atomic_fetch_add __sync_fetch_and_add
#define atomic_fetch_sub __sync_fetch_and_sub
#define atomic_fetch_and __sync_fetch_and_and
@@ -192,8 +199,15 @@
#define atomic_cmpxchg __sync_val_compare_and_swap
/* And even shorter names that return void. */
+#ifndef _GLIBCXX_ATOMIC_BUILTINS
+/* close to C11 memory_order_seq_cst */
#define atomic_inc(ptr) ((void) __sync_fetch_and_add(ptr, 1))
#define atomic_dec(ptr) ((void) __sync_fetch_and_add(ptr, -1))
+#else
+/* C11 memory_order_relaxed */
+#define atomic_inc(ptr) ((void) __atomic_fetch_add(ptr, 1,
__ATOMIC_RELAXED))
+#define atomic_dec(ptr) ((void) __atomic_fetch_add(ptr, -1,
__ATOMIC_RELAXED))
+#endif
#define atomic_add(ptr, n) ((void) __sync_fetch_and_add(ptr, n))
#define atomic_sub(ptr, n) ((void) __sync_fetch_and_sub(ptr, n))
#define atomic_and(ptr, n) ((void) __sync_fetch_and_and(ptr, n))
--
1.8.1.4
- [Qemu-devel] [PATCH] atomic: using memory_order_relaxed for refcnt inc/dec ops,
Liu Ping Fan <=