From: Harlan Stenn <stenn@ntp.org>
Date: Thu, 22 Nov 2007 07:34:27 +0000 (-0500)
Subject: [Bug 963] get_systime() is too noisy
X-Git-Tag: NTP_4_2_5P100~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7abcc62a9cac943a71d3f31292b3eead53b7f41b;p=thirdparty%2Fntp.git

[Bug 963] get_systime() is too noisy

bk: 47453103GGB6auwpRPfCTE_FHqxN1Q
---

diff --git a/ChangeLog b/ChangeLog
index 251e49dda..d334d6adc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,4 @@
+* [Bug 963] get_systime() is too noisy.
 * [Bug 960] spurious syslog:crypto_setup:spurious crypto command
 * [Bug 964] Change *-*-linux* to *-*-*linux* to allow for uclinux.
 * Changes from Dave Mills:
diff --git a/libntp/systime.c b/libntp/systime.c
index 56337ee80..95acf5005 100644
--- a/libntp/systime.c
+++ b/libntp/systime.c
@@ -25,20 +25,30 @@
 /*
  * These routines (get_systime, step_systime, adj_systime) implement an
  * interface between the system independent NTP clock and the Unix
- * system clock in various architectures and operating systems.
+ * system clock in various architectures and operating systems. Time is
+ * a precious quantity in these routines and every effort is made to
+ * minimize errors by unbiased rounding and amortizing adjustment
+ * residues.
  *
- * Time is a precious quantity in these routines and every effort is
- * made to minimize errors by always rounding toward zero and amortizing
- * adjustment residues. By default the adjustment quantum is 1 us for
- * the usual Unix tickadj() system call, but this can be increased if
- * necessary by the tick configuration command. For instance, when the
- * adjtime() quantum is a clock tick for a 100-Hz clock, the quantum
- * should be 10 ms.
+ * In order to improve the apparent resolution, provide unbiased
+ * rounding and insure that the readings cannot be predicted, the low-
+ * order unused portion of the time below the resolution limit is filled
+ * with an unbiased random fuzz.
+ *
+ * The sys_tick variable secifies the system clock tick interval in
+ * seconds and fraction. For systems that can interpolate between timer
+ * interrupts, the assumed tick interval and resolution is 1 us
+ * consistent with the timeval format used by the Unix getimeofday() abd
+ * adjtime() routines. With routines that use the timespec format, the
+ * resolution is 1 ns. For systems that cannot interpolate, such as
+ * Reliant and SCO, the resolution is as specified by the sys_tick
+ * variable, which defaults to 10 ms. The default can be changed by the
+ * tick configuration command. 
  */
 #if defined RELIANTUNIX_CLOCK || defined SCO5_CLOCK
-double	sys_tick = 10e-3;	/* 10 ms tickadj() */
+double	sys_tick = .01;		/* 10 ms resolution */
 #else
-double	sys_tick = 1e-6;	/* 1 us tickadj() */
+double	sys_tick = 1e-6;	/* 1 us resolution */
 #endif
 double	sys_residual = 0;	/* adjustment residue (s) */
 
@@ -67,7 +77,9 @@ get_systime(
 	getclock(TIMEOFDAY, &ts);
 # endif
 	now->l_i = ts.tv_sec + JAN_1970;
-	dtemp = sys_residual + (ts.tv_nsec + ntp_random() / 0.5e9) / 1e9;
+	dtemp = ts.tv_nsec + (ntp_random() * 2. / FRAC) * sys_tick *
+	    1e6;
+	dtemp = dtemp / 1e9 + sys_residual;
 	if (dtemp >= 1.) {
 		dtemp -= 1.;
 		now->l_i++;
@@ -86,7 +98,9 @@ get_systime(
 	 */
 	GETTIMEOFDAY(&tv, NULL);
 	now->l_i = tv.tv_sec + JAN_1970;
-	dtemp = sys_residual + (tv.tv_usec + ntp_random() / 0.5e6) / 1e6;
+	dtemp = ts.tv_usec + (ntp_random() * 2. / FRAC) * sys_tick *
+	    1e6;
+	dtemp = dtemp / 1e6 + sys_residual;
 	if (dtemp >= 1.) {
 		dtemp -= 1.;
 		now->l_i++;
diff --git a/ntpd/ntp_io.c b/ntpd/ntp_io.c
index 4edd4c428..02d53a7f2 100644
--- a/ntpd/ntp_io.c
+++ b/ntpd/ntp_io.c
@@ -3005,7 +3005,8 @@ static l_fp
 			l_fp nts;
 			DPRINTF(4, ("fetch_timestamp: system network time stamp: %ld.%06ld\n", tvp->tv_sec, tvp->tv_usec));
 			nts.l_i = tvp->tv_sec + JAN_1970;
-		        dtemp = (tvp->tv_usec + ntp_random() / 0.5e6) / 1e6;
+			dtemp = (tvp->tv_usec + (ntp_random() * 2. / FRAC) /
+			    1e6;
 			nts.l_uf = (u_int32)(dtemp * FRAC);
 #ifdef DEBUG_TIMING
 			{