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

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2012-03-02 01:22:40 +01:00
parent 03a99e3d5c
commit 74584b8665
1 changed files with 28 additions and 17 deletions
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45
networking/ntpd.c
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@ -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" */
}