+#define set_mb(var, value) \
+ do { xchg(&var, (value)); } while (0)
+#else
+#define smp_mb() barrier()
+#define smp_rmb() barrier()
+#define smp_wmb() barrier()
+#define smp_read_barrier_depends() do {} while(0)
+#define set_mb(var, value) \
+ do { var = (value); barrier(); } while (0)
+#endif