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diff --git a/src/threads/synch.h b/src/threads/synch.h
index 9e464e3876400f60fafbc44a105f859ffd4b6938..a19e88b181dff1208839ff890154aa69b299ce91 100644 (file)
--- a/src/threads/synch.h
+++ b/src/threads/synch.h
@@ -44,7 +44,8 @@ void cond_broadcast (struct condition *, struct lock *);
 /* Optimization barrier.
 
    The compiler will not reorder operations across an
-   optimization barrier. */
+   optimization barrier.  See "Optimization Barriers" in the
+   reference guide for more information.*/
 #define barrier() asm volatile ("" : : : "memory")
 
 #endif /* threads/synch.h */