Index: sys/sys/callout.h
===================================================================
--- sys/sys/callout.h	(revision 242707)
+++ sys/sys/callout.h	(working copy)
@@ -51,29 +51,20 @@
 #define	CALLOUT_DIRECT 		0x0100 /* allow exec from hw int context */
 
 #define	C_DIRECT_EXEC		0x0001 /* direct execution of callout */
-#define	C_P1S			0x0002 /* fields related to precision */ 
-#define	C_P500MS		0x0006 	
-#define	C_P250MS		0x000a 	
-#define	C_P125MS		0x000e
-#define	C_P64MS			0x0012
-#define	C_P32MS			0x0016
-#define	C_P16MS			0x001a
-#define	C_P8MS			0x001e
-#define	C_P4MS			0x0022
-#define	C_P2MS			0x0026
-#define	C_P1MS			0x002a
-#define	C_P500US		0x002e
-#define	C_P250US		0x0032
-#define	C_P125US		0x0036
-#define	C_P64US			0x003a
-#define	C_P32US			0x003e
-#define	C_P16US			0x0042
-#define	C_P8US			0x0046
-#define	C_P4US			0x004a
-#define	C_P2US			0x004e
-#define	PRECISION_BITS		7	
+#define	C_PRECISION		0x0002 /* precision for callout specified */
+#define	PRECISION_BITS		24
 #define	PRECISION_RANGE		((1 << PRECISION_BITS) - 1)	
+#define	PRECISION_MASK		(1 << ((32 - PRECISION_BITS) - 1))
+#define	T2PRECFLAGS(x)		((x) * 4294) & PRECISION_MASK) 
+#define	PRECBTGET(x)		((uint64_t)(flags & PRECISION_MASK) << 32)
 
+/*
+ * Common values specified for precision.
+ */
+#define	C_P1MS			T2PRECFLAGS(1000)
+#define	C_P10MS			T2PRECFLAGS(10000)
+#define	C_P100MS		T2PRECFLAGS(100000)
+
 struct callout_handle {
 	struct callout *callout;
 };
Index: sys/kern/kern_timeout.c
===================================================================
--- sys/kern/kern_timeout.c	(revision 242707)
+++ sys/kern/kern_timeout.c	(working copy)
@@ -170,7 +170,6 @@ struct callout_cpu cc_cpu;
 #define	CC_LOCK(cc)	mtx_lock_spin(&(cc)->cc_lock)
 #define	CC_UNLOCK(cc)	mtx_unlock_spin(&(cc)->cc_lock)
 #define	CC_LOCK_ASSERT(cc)	mtx_assert(&(cc)->cc_lock, MA_OWNED)
-#define	C_PRECISION	0x2
 
 #define FREQ2BT(freq, bt)                                               \
 {                                                                       \
@@ -576,8 +575,8 @@ callout_cc_add(struct callout *c, struct callout_c
 {
 	struct bintime bt;
 	uint64_t r_val;
-	int bucket, r_shift;
-	
+	int bucket;
+
 	CC_LOCK_ASSERT(cc);
 	if (bintime_cmp(&to_bintime, &cc->cc_lastscan, <))
 		to_bintime = cc->cc_lastscan;
@@ -590,33 +589,10 @@ callout_cc_add(struct callout *c, struct callout_c
 	c->c_time = to_bintime;
 	bintime_clear(&c->c_precision);
 	if (flags & C_PRECISION) {
-		r_shift = ((flags >> 2) & PRECISION_RANGE);
-		r_val = (r_shift != 0) ? (uint64_t)1 << (64 - r_shift) : 0;
-		/*
-		 * Round as far as precision specified is coarse (up to 8ms).
-		 * In order to play safe, round to to half of the interval and
-		 * set half precision.
-		 */
-		if (r_shift < 6) {
-			r_val = (r_shift != 0) ? r_val >> 2 :
-			    ((uint64_t)1 << (64 - 1)) - 1;
-			/*
-			 * Round only if c_time is not a multiple of the
-			 * rounding factor.
-			 */
-			if ((c->c_time.frac & r_val) != r_val) {
-				c->c_time.frac |= r_val - 1;
-				c->c_time.frac += 1;
-				if (c->c_time.frac == 0)
-					c->c_time.sec += 1;
-			}
-		}
+		r_val = PRECBTGET(flags);
 		c->c_precision.frac = r_val;
-		CTR6(KTR_CALLOUT, "rounding %d.%08x%08x to %d.%08x%08x",
-		    to_bintime.sec, (u_int) (to_bintime.frac >> 32),
-		    (u_int) (to_bintime.frac & 0xffffffff), c->c_time.sec,
-		    (u_int) (c->c_time.frac >> 32),
-		    (u_int) (c->c_time.frac & 0xffffffff)); 
+		CTR3(KTR_CALLOUT, "precision set for %p: 0.%08x%08",
+		    c, (u_int) (r_val >> 32), (u_int) (r_val & 0xffffffff));
 	} 
 	bucket = get_bucket(&c->c_time);
 	TAILQ_INSERT_TAIL(&cc->cc_callwheel[bucket], c, c_links.tqe);