74584b866
Denys Vlasenko
2012-03-02
Subject
ntpd: log jitter on update too; increase assumed clock precision x2 - to 2ms
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networking/ntpd.c+28 -17
| @@ -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" */ | |
| } | |