Anti-clockhop hysteresis stuff from Dave Mills.

bk: 3b8877ad8jnfoFYcEID9V72sFaWcPA

diff --git a/include/ntp.h b/include/ntp.h
index 531d5e6d6058711e9e349ce109c19fcafc5ce127..0a004e48e2e754fee484d346ceb0b1e3b2edc1c6 100644 (file)
--- 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 91c2a6286b86f0d0118a5c36379a0ffd1ff8339a..12b82001d356fd19d0d3bd3bf08110dbdf5ece82 100644 (file)
--- 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;