Index: sys/sys/ktr.h
===================================================================
--- sys/sys/ktr.h	(revision 238497)
+++ sys/sys/ktr.h	(working copy)
@@ -75,6 +75,7 @@
 #define	KTR_INET6	0x10000000		/* IPv6 stack */
 #define	KTR_SCHED	0x20000000		/* Machine parsed sched info. */
 #define	KTR_BUF		0x40000000		/* Buffer cache */
+#define	KTR_LATENCY	0x80000000		/* latency measurements */
 #define	KTR_ALL		0x7fffffff
 
 /* Trace classes to compile in */
Index: sys/kern/kern_clocksource.c
===================================================================
--- sys/kern/kern_clocksource.c	(revision 238512)
+++ sys/kern/kern_clocksource.c	(working copy)
@@ -347,12 +347,13 @@ getnextevent(struct bintime *event)
 static void
 timercb(struct eventtimer *et, void *arg)
 {
-	struct bintime now;
+	struct bintime now, delta;
 	struct bintime *next;
 	struct pcpu_state *state;
 #ifdef SMP
 	int cpu, bcast;
 #endif
+	uint64_t musec;
 
 	/* Do not touch anything if somebody reconfiguring timers. */
 	if (busy)
@@ -363,7 +364,11 @@ timercb(struct eventtimer *et, void *arg)
 		next = &state->nexttick;
 	} else
 		next = &nexttick;
-	binuptime(&now); 
+	binuptime(&now);
+	delta = now;
+	bintime_sub(&delta, &state->nextevent);
+	musec = ((uint64_t)1000000 * (uint32_t)(delta.frac >> 32)) >> 32;
+	CTR1(KTR_LATENCY, "intr delta: %lu", musec);
 	if (periodic) { 
 		*next = now;
 		bintime_add(next, &timerperiod); /* Next tick in 1 period. */