ntpd: log jitter on update too; increase assumed clock precision x2 - to 2ms

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/networking/ntpd.c b/networking/ntpd.c
index a8738951fae4ef284c98eff5061206822a952154..e7e9922054c45ffa6fb8f7014959754c05651771 100644 (file)
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -276,11 +276,12 @@ struct globals {
        unsigned verbose;
        unsigned peer_cnt;
        /* refid: 32-bit code identifying the particular server or reference clock
-        *  in stratum 0 packets this is a four-character ASCII string,
-        *  called the kiss code, used for debugging and monitoring
-        *  in stratum 1 packets this is a four-character ASCII string
-        *  assigned to the reference clock by IANA. Example: "GPS "
-        *  in stratum 2+ packets, it's IPv4 address or 4 first bytes of MD5 hash of IPv6
+        * in stratum 0 packets this is a four-character ASCII string,
+        * called the kiss code, used for debugging and monitoring
+        * in stratum 1 packets this is a four-character ASCII string
+        * assigned to the reference clock by IANA. Example: "GPS "
+        * in stratum 2+ packets, it's IPv4 address or 4 first bytes
+        * of MD5 hash of IPv6
         */
        uint32_t refid;
        uint8_t  ntp_status;
@@ -289,27 +290,35 @@ struct globals {
         * mains-frequency clock incrementing at 60 Hz is 16 ms, even when the
         * system clock hardware representation is to the nanosecond.
         *
-        * Delays, jitters of various kinds are clamper down to precision.
+        * Delays, jitters of various kinds are clamped down to precision.
         *
         * If precision_sec is too large, discipline_jitter gets clamped to it
-        * and if offset is much smaller than discipline_jitter, poll interval
-        * grows even though we really can benefit from staying at smaller one,
-        * collecting non-lagged datapoits and correcting the offset.
+        * and if offset is smaller than discipline_jitter * POLLADJ_GATE, poll
+        * interval grows even though we really can benefit from staying at
+        * smaller one, collecting non-lagged datapoits and correcting offset.
         * (Lagged datapoits exist when poll_exp is large but we still have
         * systematic offset error - the time distance between datapoints
-        * is significat and older datapoints have smaller offsets.
+        * is significant and older datapoints have smaller offsets.
         * This makes our offset estimation a bit smaller than reality)
         * Due to this effect, setting G_precision_sec close to
         * STEP_THRESHOLD isn't such a good idea - offsets may grow
         * too big and we will step. I observed it with -6.
         *
-        * OTOH, setting precision too small would result in futile attempts
-        * to syncronize to the unachievable precision.
+        * OTOH, setting precision_sec far too small would result in futile
+        * attempts to syncronize to an unachievable precision.
         *
         * -6 is 1/64 sec, -7 is 1/128 sec and so on.
+        * -8 is 1/256 ~= 0.003906 (worked well for me --vda)
+        * -9 is 1/512 ~= 0.001953 (let's try this for some time)
         */
-#define G_precision_exp  -8
-#define G_precision_sec  (1.0 / (1 << (- G_precision_exp)))
+#define G_precision_exp  -9
+       /*
+        * G_precision_exp is used only for construction outgoing packets.
+        * It's ok to set G_precision_sec to a slightly different value
+        * (One which is "nicer looking" in logs).
+        * Exact value would be (1.0 / (1 << (- G_precision_exp))):
+        */
+#define G_precision_sec  0.002
        uint8_t  stratum;
        /* Bool. After set to 1, never goes back to 0: */
        smallint initial_poll_complete;
@@ -1334,8 +1343,10 @@ update_local_clock(peer_t *p)
                 * weighted offset differences. Used by the poll adjust code.
                 */
                etemp = SQUARE(G.discipline_jitter);
-               dtemp = SQUARE(MAXD(fabs(offset - G.last_update_offset), G_precision_sec));
+               dtemp = SQUARE(offset - G.last_update_offset);
                G.discipline_jitter = SQRT(etemp + (dtemp - etemp) / AVG);
+               if (G.discipline_jitter < G_precision_sec)
+                       G.discipline_jitter = G_precision_sec;
                VERB3 bb_error_msg("discipline jitter=%f", G.discipline_jitter);
 
                switch (G.discipline_state) {
@@ -1495,8 +1506,8 @@ update_local_clock(peer_t *p)
        }
 #endif
        G.kernel_freq_drift = tmx.freq / 65536;
-       VERB2 bb_error_msg("update peer:%s, offset:%+f, clock drift:%+ld ppm",
-                       p->p_dotted, G.last_update_offset, G.kernel_freq_drift);
+       VERB2 bb_error_msg("update peer:%s, offset:%+f, jitter:%f, clock drift:%+ld ppm",
+                       p->p_dotted, G.last_update_offset, G.discipline_jitter, G.kernel_freq_drift);
 
        return 1; /* "ok to increase poll interval" */
 }