From: Harlan Stenn <stenn@ntp.org>
Date: Sun, 26 Aug 2001 04:14:37 +0000 (-0400)
Subject: Anti-clockhop hysteresis stuff from Dave Mills.
X-Git-Tag: NTP_4_1_71~20
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e724ffb5c2317d56217d382e6dc51defd4ccd910;p=thirdparty%2Fntp.git

Anti-clockhop hysteresis stuff from Dave Mills.

bk: 3b8877ad8jnfoFYcEID9V72sFaWcPA
---

diff --git a/include/ntp.h b/include/ntp.h
index 531d5e6d60..0a004e48e2 100644
--- a/include/ntp.h
+++ b/include/ntp.h
@@ -111,6 +111,8 @@ typedef char s_char;
 #define BURST_INTERVAL1	4	/* first interburst interval (log2) */
 #define BURST_INTERVAL2	1	/* succeeding interburst intervals (log2) */
 #define HUFFPUFF	900	/* huff-n'-puff sample interval (s) */
+#define HYST		.5	/* anti-clockhop hysteresis */
+#define HYST_TC		.5	/* anti-clockhop hysteresis decay factor */
 
 /*
  * Operations for jitter calculations (these use doubles).
@@ -304,6 +306,7 @@ struct peer {
 	double	jitter;		/* peer jitter (squares) */
 	double	disp;		/* peer dispersion */
 	double	estbdelay;	/* clock offset to broadcast server */
+	double	hyst;		/* anti-clockhop hysteresis */
 
 	/*
 	 * Variables set by received packet
diff --git a/ntpd/ntp_proto.c b/ntpd/ntp_proto.c
index 91c2a6286b..12b82001d3 100644
--- a/ntpd/ntp_proto.c
+++ b/ntpd/ntp_proto.c
@@ -163,6 +163,7 @@ transmit(
 			peer->flags |= FLAG_CLUST;
 		oreach = peer->reach;
 		peer->reach <<= 1;
+		peer->hyst *= HYST_TC;
 		if (peer->reach == 0) {
 
 			/*
@@ -1809,6 +1810,10 @@ clock_select(void)
 	 * drowned as well, but only if at at least eight poll intervals
 	 * have gone by. We must leave at least one peer to collect the
 	 * million bucks.
+	 *
+	 * Note the hysteresis gimmick that decreases the effective
+	 * distance for those rascals that previously have made the
+	 * final cut. This to discourage clockhopping.
 	 */
 	j = 0;
 	for (i = 0; i < nlist; i++) {
@@ -1821,7 +1826,8 @@ clock_select(void)
 			continue;
 		}
 		peer->status = CTL_PST_SEL_DISTSYSPEER;
-		d = root_distance(peer) + peer->stratum * MAXDISPERSE;
+		d = (1. - peer->hyst) * root_distance(peer) +
+		    peer->stratum * MAXDISPERSE;
 		if (j >= NTP_MAXCLOCK) {
 			if (d >= synch[j - 1])
 				continue;
@@ -1955,6 +1961,7 @@ clock_select(void)
 		peer = peer_list[i];
 		peer->status = CTL_PST_SEL_SYNCCAND;
 		peer->flags |= FLAG_SYSPEER;
+		peer->hyst = HYST;
 		poll_update(peer, peer->hpoll);
 		if (peer->stratum == peer_list[0]->stratum) {
 			leap_consensus |= peer->leap;