--- a/hotspot/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp	Tue Mar 24 15:09:52 2009 -0700
+++ b/hotspot/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp	Thu Mar 26 14:31:45 2009 -0700
@@ -44,11 +44,12 @@
 
 inline void OrderAccess::fence() {
   if (os::is_MP()) {
+    // always use locked addl since mfence is sometimes expensive
 #ifdef AMD64
-    __asm__ __volatile__ ("mfence":::"memory");
+    __asm__ volatile ("lock; addl $0,0(%%rsp)" : : : "cc", "memory");
 #else
     __asm__ volatile ("lock; addl $0,0(%%esp)" : : : "cc", "memory");
-#endif // AMD64
+#endif
   }
 }