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authorDenys Vlasenko <vda.linux@googlemail.com>2012-03-02 00:22:40 (GMT)
committer Denys Vlasenko <vda.linux@googlemail.com>2012-03-02 00:22:40 (GMT)
commit74584b86656113391763a21ea32fbff6d9fb6a9a (patch)
tree785d1923cad151c655f73559cbb2426281aeb453
parent03a99e3d5c654d3dd8103199e20c8252dab8e091 (diff)
downloadbusybox-74584b86656113391763a21ea32fbff6d9fb6a9a.tar.gz
busybox-74584b86656113391763a21ea32fbff6d9fb6a9a.tar.bz2
ntpd: log jitter on update too; increase assumed clock precision x2 - to 2ms
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--networking/ntpd.c45
1 files changed, 28 insertions, 17 deletions
diff --git a/networking/ntpd.c b/networking/ntpd.c
index a873895..e7e9922 100644
--- 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" */
}