Index: sys/kern/kern_time.c
===================================================================
--- sys/kern/kern_time.c	(revision 239329)
+++ sys/kern/kern_time.c	(working copy)
@@ -53,6 +53,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/time.h>
 #include <sys/timers.h>
 #include <sys/timetc.h>
+#include <sys/types.h>
 #include <sys/vnode.h>
 
 #include <vm/vm.h>
@@ -60,6 +61,13 @@ __FBSDID("$FreeBSD$");
 
 #define MAX_CLOCKS 	(CLOCK_MONOTONIC+1)
 
+#define TIMESEL(x, bt)							\
+   (((x) < (nanosleep_precision)) ? binuptime(&bt) : getbinuptime(&bt))
+
+static int nanosleep_precision;
+SYSCTL_INT(_kern, OID_AUTO, nanosleep_precision, CTLFLAG_RW, 
+    &nanosleep_precision, 0, "Precision threshold for nanosleep function"); 
+
 static struct kclock	posix_clocks[MAX_CLOCKS];
 static uma_zone_t	itimer_zone = NULL;
 
@@ -105,7 +113,15 @@ int		itimespecfix(struct timespec *ts);
 
 SYSINIT(posix_timer, SI_SUB_P1003_1B, SI_ORDER_FIRST+4, itimer_start, NULL);
 
+static void
+init_precision(void)
+{
+	
+	nanosleep_precision = 20 * imin(1000000000 / hz, 1000000); 
+}
 
+SYSINIT(init_precision, SI_SUB_SOFTINTR, SI_ORDER_ANY, init_precision, NULL);
+
 static int
 settime(struct thread *td, struct timeval *tv)
 {
@@ -361,13 +377,13 @@ kern_nanosleep(struct thread *td, struct timespec
 		return (EINVAL);
 	if (rqt->tv_sec < 0 || (rqt->tv_sec == 0 && rqt->tv_nsec == 0))
 		return (0);
-	binuptime(&bt);
+	TIMESEL(rqt->tv_nsec, bt);
 	timespec2bintime(rqt, &tmp);
 	bintime_add(&bt,&tmp);
 	for (;;) {
 		error = tsleep_bt(&nanowait, PWAIT | PCATCH, "nanslp", &bt, 
 		    C_DIRECT_EXEC);
-		binuptime(&bt2);
+		TIMESEL(rqt->tv_nsec, bt2);
 		if (error != EWOULDBLOCK) {
 			if (error == ERESTART)
 				error = EINTR;