132b044f4
Denys Vlasenko
2012-03-05
Subject
ntpd: experimental code to correct frequency a bit more aggressively
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networking/ntpd.c+29 -23
| @@ -138,6 +138,7 @@ | |
| * by staying at smaller poll). | |
| */ | |
| #define POLLADJ_GATE 4 | |
| + | #define TIMECONST_HACK_GATE 2 |
| /* Compromise Allan intercept (sec). doc uses 1500, std ntpd uses 512 */ | |
| #define ALLAN 512 | |
| /* PLL loop gain */ | |
| @@ -339,6 +340,7 @@ struct globals { | |
| double last_update_offset; // c.last | |
| double last_update_recv_time; // s.t | |
| double discipline_jitter; // c.jitter | |
| + | double offset_to_jitter_ratio; |
| //double cluster_offset; // s.offset | |
| //double cluster_jitter; // s.jitter | |
| #if !USING_KERNEL_PLL_LOOP | |
| @@ -1337,7 +1339,8 @@ update_local_clock(peer_t *p) | |
| return 1; /* "ok to increase poll interval" */ | |
| } | |
| #endif | |
| - | set_new_values(STATE_SYNC, /*offset:*/ 0, recv_time); |
| + | offset = 0; |
| + | set_new_values(STATE_SYNC, offset, recv_time); |
| } else { /* abs_offset <= STEP_THRESHOLD */ | |
| @@ -1355,6 +1358,7 @@ update_local_clock(peer_t *p) | |
| G.discipline_jitter = SQRT(etemp + (dtemp - etemp) / AVG); | |
| if (G.discipline_jitter < G_precision_sec) | |
| G.discipline_jitter = G_precision_sec; | |
| + | G.offset_to_jitter_ratio = fabs(offset) / G.discipline_jitter; |
| VERB3 bb_error_msg("discipline jitter=%f", G.discipline_jitter); | |
| switch (G.discipline_state) { | |
| @@ -1443,7 +1447,7 @@ update_local_clock(peer_t *p) | |
| /* We are in STATE_SYNC now, but did not do adjtimex yet. | |
| * (Any other state does not reach this, they all return earlier) | |
| - | * By this time, freq_drift and G.last_update_offset are set |
| + | * By this time, freq_drift and offset are set |
| * to values suitable for adjtimex. | |
| */ | |
| #if !USING_KERNEL_PLL_LOOP | |
| @@ -1482,40 +1486,42 @@ update_local_clock(peer_t *p) | |
| tmx.modes = ADJ_FREQUENCY | ADJ_OFFSET; | |
| /* 65536 is one ppm */ | |
| tmx.freq = G.discipline_freq_drift * 65536e6; | |
| - | tmx.offset = G.last_update_offset * 1000000; /* usec */ |
| #endif | |
| tmx.modes = ADJ_OFFSET | ADJ_STATUS | ADJ_TIMECONST;// | ADJ_MAXERROR | ADJ_ESTERROR; | |
| - | tmx.offset = (G.last_update_offset * 1000000); /* usec */ |
| - | /* + (G.last_update_offset < 0 ? -0.5 : 0.5) - too small to bother */ |
| + | tmx.offset = (offset * 1000000); /* usec */ |
| tmx.status = STA_PLL; | |
| if (G.ntp_status & LI_PLUSSEC) | |
| tmx.status |= STA_INS; | |
| if (G.ntp_status & LI_MINUSSEC) | |
| tmx.status |= STA_DEL; | |
| + | |
| tmx.constant = G.poll_exp - 4; | |
| - | //tmx.esterror = (u_int32)(clock_jitter * 1e6); |
| - | //tmx.maxerror = (u_int32)((sys_rootdelay / 2 + sys_rootdisp) * 1e6); |
| + | /* EXPERIMENTAL. |
| + | * The below if statement should be unnecessary, but... |
| + | * It looks like Linux kernel's PLL is far too gentle in changing |
| + | * tmx.freq in response to clock offset. Offset keeps growing |
| + | * and eventually we fall back to smaller poll intervals. |
| + | * We can make correction more agressive (about x2) by supplying |
| + | * PLL time constant which is one less than the real one. |
| + | * To be on a safe side, let's do it only if offset is significantly |
| + | * larger than jitter. |
| + | */ |
| + | if (tmx.constant > 0 && G.offset_to_jitter_ratio > TIMECONST_HACK_GATE) |
| + | tmx.constant--; |
| + | |
| + | //tmx.esterror = (uint32_t)(clock_jitter * 1e6); |
| + | //tmx.maxerror = (uint32_t)((sys_rootdelay / 2 + sys_rootdisp) * 1e6); |
| rc = adjtimex(&tmx); | |
| if (rc < 0) | |
| bb_perror_msg_and_die("adjtimex"); | |
| /* NB: here kernel returns constant == G.poll_exp, not == G.poll_exp - 4. | |
| * Not sure why. Perhaps it is normal. | |
| */ | |
| - | VERB3 bb_error_msg("adjtimex:%d freq:%ld offset:%+ld constant:%ld status:0x%x", |
| - | rc, tmx.freq, tmx.offset, tmx.constant, tmx.status); |
| - | #if 0 |
| - | VERB3 { |
| - | /* always gives the same output as above msg */ |
| - | memset(&tmx, 0, sizeof(tmx)); |
| - | if (adjtimex(&tmx) < 0) |
| - | bb_perror_msg_and_die("adjtimex"); |
| - | VERB3 bb_error_msg("c adjtimex freq:%ld offset:%+ld constant:%ld status:0x%x", |
| - | tmx.freq, tmx.offset, tmx.constant, tmx.status); |
| - | } |
| - | #endif |
| + | VERB3 bb_error_msg("adjtimex:%d freq:%ld offset:%+ld status:0x%x", |
| + | rc, tmx.freq, tmx.offset, tmx.status); |
| G.kernel_freq_drift = tmx.freq / 65536; | |
| - | VERB2 bb_error_msg("update peer:%s, offset:%+f, jitter:%f, clock drift:%+.3f ppm", |
| - | p->p_dotted, G.last_update_offset, G.discipline_jitter, (double)tmx.freq / 65536); |
| + | VERB2 bb_error_msg("update peer:%s, offset:%+f, jitter:%f, clock drift:%+.3f ppm, tc:%d", |
| + | p->p_dotted, offset, G.discipline_jitter, (double)tmx.freq / 65536, (int)tmx.constant); |
| return 1; /* "ok to increase poll interval" */ | |
| } | |
| @@ -1651,7 +1657,7 @@ recv_and_process_peer_pkt(peer_t *p) | |
| if (!p->reachable_bits) { | |
| /* 1st datapoint ever - replicate offset in every element */ | |
| int i; | |
| - | for (i = 1; i < NUM_DATAPOINTS; i++) { |
| + | for (i = 0; i < NUM_DATAPOINTS; i++) { |
| p->filter_datapoint[i].d_offset = datapoint->d_offset; | |
| } | |
| } | |
| @@ -1706,7 +1712,7 @@ recv_and_process_peer_pkt(peer_t *p) | |
| ? "grows" : "falls" | |
| ); | |
| } | |
| - | if (rc > 0 && fabs(q->filter_offset) < POLLADJ_GATE * G.discipline_jitter) { |
| + | if (rc > 0 && G.offset_to_jitter_ratio < POLLADJ_GATE) { |
| /* was += G.poll_exp but it is a bit | |
| * too optimistic for my taste at high poll_exp's */ | |
| G.polladj_count += MINPOLL; | |