[ovs-dev] [PATCH 02/12] ovs-atomic: Use memory_order_relaxed for ovs_refcount.

[Jarno Rajahalme]

Updating the reference count only requires atomicity, but no memory
ordering with respect to any other loads or stores.  Avoiding the
overhead of the default memory_order_seq_cst can make these more
efficient.

Signed-off-by: Jarno Rajahalme <jrajahalme at nicira.com>
---
 lib/ovs-atomic.h |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/ovs-atomic.h b/lib/ovs-atomic.h
index 2452846..1a721ca 100644
--- a/lib/ovs-atomic.h
+++ b/lib/ovs-atomic.h
@@ -320,7 +320,8 @@ ovs_refcount_ref(struct ovs_refcount *refcount)
 {
     unsigned int old_refcount;
 
-    atomic_add(&refcount->count, 1, &old_refcount);
+    atomic_add_explicit(&refcount->count, 1, &old_refcount,
+                        memory_order_relaxed);
     ovs_assert(old_refcount > 0);
 }
 
@@ -337,7 +338,8 @@ ovs_refcount_unref(struct ovs_refcount *refcount)
 {
     unsigned int old_refcount;
 
-    atomic_sub(&refcount->count, 1, &old_refcount);
+    atomic_sub_explicit(&refcount->count, 1, &old_refcount,
+                        memory_order_relaxed);
     ovs_assert(old_refcount > 0);
     return old_refcount;
 }
@@ -352,7 +354,7 @@ ovs_refcount_read(const struct ovs_refcount *refcount_)
         = CONST_CAST(struct ovs_refcount *, refcount_);
     unsigned int count;
 
-    atomic_read(&refcount->count, &count);
+    atomic_read_explicit(&refcount->count, &count, memory_order_relaxed);
     return count;
 }
 
-- 
1.7.10.4