X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=urcu-static.h;h=66a06df85e0f72080bdb79a991e0f5d3e8691125;hb=cee02f0ab0a6766662490f2d815d487c098c17b1;hp=1b3527fd2de649b087a502ec42af2098ba095ec3;hpb=67ef1a2cd793e5dde7db32ef5210fc002c3325cd;p=urcu.git

diff --git a/urcu-static.h b/urcu-static.h
index 1b3527f..66a06df 100644
--- a/urcu-static.h
+++ b/urcu-static.h
@@ -76,6 +76,15 @@
  * Inserts memory barriers on architectures that require them (currently only
  * Alpha) and documents which pointers are protected by RCU.
  *
+ * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
+ * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
+ * data read before the pointer read by speculating the value of the pointer.
+ * Correct ordering is ensured because the pointer is read as a volatile access.
+ * This acts as a global side-effect operation, which forbids reordering of
+ * dependent memory operations. Note that such concern about dependency-breaking
+ * optimizations will eventually be taken care of by the "memory_order_consume"
+ * addition to forthcoming C++ standard.
+ *
  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  */
 
@@ -117,8 +126,11 @@
 #define YIELD_READ 	(1 << 0)
 #define YIELD_WRITE	(1 << 1)
 
-/* Updates without DEBUG_FULL_MB are much slower. Account this in the delay */
-#ifdef DEBUG_FULL_MB
+/*
+ * Updates without CONFIG_URCU_AVOID_SIGNALS are much slower. Account this in
+ * the delay.
+ */
+#ifdef CONFIG_URCU_AVOID_SIGNALS
 /* maximum sleep delay, in us */
 #define MAX_SLEEP 50
 #else
@@ -161,7 +173,7 @@ static inline void debug_yield_init(void)
 }
 #endif
 
-#ifdef DEBUG_FULL_MB
+#ifdef CONFIG_URCU_AVOID_SIGNALS
 static inline void reader_barrier()
 {
 	smp_mb();