diff --git a/sys/kern/kern_time.c b/sys/kern/kern_time.c
index 169d5e0fd74a..2d53d3fb892d 100644
--- a/sys/kern/kern_time.c
+++ b/sys/kern/kern_time.c
@@ -664,21 +664,8 @@ timevalfix(struct timeval *t1)
 	}
 }
 
-#ifndef timersub
-#define timersub(tvp, uvp, vvp)						\
-	do {								\
-		(vvp)->tv_sec = (tvp)->tv_sec - (uvp)->tv_sec;		\
-		(vvp)->tv_usec = (tvp)->tv_usec - (uvp)->tv_usec;	\
-		if ((vvp)->tv_usec < 0) {				\
-			(vvp)->tv_sec--;				\
-			(vvp)->tv_usec += 1000000;			\
-		}							\
-	} while (0)
-#endif
-
 /*
- * ratecheck(): simple time-based rate-limit checking.  see ratecheck(9)
- * for usage and rationale.
+ * ratecheck(): simple time-based rate-limit checking.
  */
 int
 ratecheck(struct timeval *lasttime, const struct timeval *mininterval)
@@ -686,8 +673,9 @@ ratecheck(struct timeval *lasttime, const struct timeval *mininterval)
 	struct timeval tv, delta;
 	int rv = 0;
 
-	getmicrouptime(&tv);
-	timersub(&tv, lasttime, &delta);
+	getmicrouptime(&tv);		/* NB: 10ms precision */
+	delta = tv;
+	timevalsub(&delta, lasttime);
 
 	/*
 	 * check for 0,0 is so that the message will be seen at least once,
@@ -704,50 +692,31 @@ ratecheck(struct timeval *lasttime, const struct timeval *mininterval)
 
 /*
  * ppsratecheck(): packets (or events) per second limitation.
+ *
+ * Return 0 if the limit is to be enforced (e.g. the caller
+ * should drop a packet because of the rate limitation).
+ *
+ * Note that we maintain the struct timeval for compatibility
+ * with other bsd systems.  We reuse the storage and just monitor
+ * clock ticks for minimal overhead.  
  */
 int
 ppsratecheck(struct timeval *lasttime, int *curpps, int maxpps)
 {
-	struct timeval tv, delta;
-	int rv;
-
-	getmicrouptime(&tv);
-	timersub(&tv, lasttime, &delta);
+	int now;
 
 	/*
-	 * check for 0,0 is so that the message will be seen at least once.
-	 * if more than one second have passed since the last update of
-	 * lasttime, reset the counter.
-	 *
-	 * we do increment *curpps even in *curpps < maxpps case, as some may
-	 * try to use *curpps for stat purposes as well.
+	 * Reset the last time and counter if this is the first call
+	 * or more than a second has passed since the last update of
+	 * lasttime.
 	 */
-	if ((lasttime->tv_sec == 0 && lasttime->tv_usec == 0) ||
-	    delta.tv_sec >= 1) {
-		*lasttime = tv;
-		*curpps = 0;
-		rv = 1;
-	} else if (maxpps < 0)
-		rv = 1;
-	else if (*curpps < maxpps)
-		rv = 1;
-	else
-		rv = 0;
-
-#if 1 /*DIAGNOSTIC?*/
-	/* be careful about wrap-around */
-	if (*curpps + 1 > *curpps)
-		*curpps = *curpps + 1;
-#else
-	/*
-	 * assume that there's not too many calls to this function.
-	 * not sure if the assumption holds, as it depends on *caller's*
-	 * behavior, not the behavior of this function.
-	 * IMHO it is wrong to make assumption on the caller's behavior,
-	 * so the above #if is #if 1, not #ifdef DIAGNOSTIC.
-	 */
-	*curpps = *curpps + 1;
-#endif
-
-	return (rv);
+	now = ticks;
+	if (lasttime->tv_sec == 0 || (u_int)(now - lasttime->tv_sec) >= hz) {
+		lasttime->tv_sec = now;
+		*curpps = 1;
+		return (1);
+	} else {
+		(*curpps)++;		/* NB: ignore potential overflow */
+		return (maxpps < 0 || *curpps < maxpps);
+	}
 }