+#define USEC_PER_MS (1000LL)
+#define MSEC_PER_SEC (1000LL)
+#define NSEC_PER_USEC (1000LL)
+#define USEC_PER_SEC (MSEC_PER_SEC * USEC_PER_MS)
+#define NSEC_PER_SEC (NSEC_PER_USEC * USEC_PER_SEC)
+#define SEC_PER_NSEC ((f64)1/NSEC_PER_SEC)
+
+/** timing wheel tick-rate, 1ms should be good enough */
+#define BFD_TW_TPS (MSEC_PER_SEC)