d9109e3b4
Denys Vlasenko
2010-01-02
Subject
ntpd: improve frequency filtering
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networking/ntpd.c+43 -21
| @@ -390,8 +390,13 @@ static void | |
| filter_datapoints(peer_t *p, double t) | |
| { | |
| int i, idx; | |
| + | int got_newest; |
| double minoff, maxoff, wavg, sum, w; | |
| - | double x = x; |
| + | double x = x; /* for compiler */ |
| + | double oldest_off = oldest_off; |
| + | double oldest_age = oldest_age; |
| + | double newest_off = newest_off; |
| + | double newest_age = newest_age; |
| minoff = maxoff = p->filter_datapoint[0].d_offset; | |
| for (i = 1; i < NUM_DATAPOINTS; i++) { | |
| @@ -416,6 +421,7 @@ filter_datapoints(peer_t *p, double t) | |
| // / (i+1) | |
| // --- 2 | |
| // i=0 | |
| + | got_newest = 0; |
| sum = 0; | |
| for (i = 0; i < NUM_DATAPOINTS; i++) { | |
| VERB4 { | |
| @@ -437,23 +443,36 @@ filter_datapoints(peer_t *p, double t) | |
| if (maxoff == p->filter_datapoint[idx].d_offset) { | |
| maxoff += 1; | |
| } else { | |
| - | x = p->filter_datapoint[idx].d_offset * w; |
| + | oldest_off = p->filter_datapoint[idx].d_offset; |
| + | oldest_age = t - p->filter_datapoint[idx].d_recv_time; |
| + | if (!got_newest) { |
| + | got_newest = 1; |
| + | newest_off = oldest_off; |
| + | newest_age = oldest_age; |
| + | } |
| + | x = oldest_off * w; |
| wavg += x; | |
| w /= 2; | |
| } | |
| idx = (idx - 1) & (NUM_DATAPOINTS - 1); | |
| } | |
| + | p->filter_dispersion = sum; |
| wavg += x; /* add another older6/64 to form older6/32 */ | |
| + | /* Fix systematic underestimation with large poll intervals. |
| + | * Imagine that we still have a bit of uncorrected drift, |
| + | * and poll interval is big (say, 100 sec). Offsets form a progression: |
| + | * 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 - 0.7 is most recent. |
| + | * The algorithm above drops 0.0 and 0.7 as outliers, |
| + | * and then we have this estimation, ~25% off from 0.7: |
| + | * 0.1/32 + 0.2/32 + 0.3/16 + 0.4/8 + 0.5/4 + 0.6/2 = 0.503125 |
| + | */ |
| + | x = newest_age / (oldest_age - newest_age); /* in above example, 100 / (600 - 100) */ |
| + | if (x < 1) { |
| + | x = (newest_off - oldest_off) * x; /* 0.5 * 100/500 = 0.1 */ |
| + | wavg += x; |
| + | } |
| p->filter_offset = wavg; | |
| - | p->filter_dispersion = sum; |
| - | //TODO: fix systematic underestimation with large poll intervals. |
| - | // Imagine that we still have a bit of uncorrected drift, |
| - | // and poll interval is big. Offsets form a progression: |
| - | // 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7, 0.7 is most recent. |
| - | // The algorithm above drops 0.0 and 0.7 as outliers, |
| - | // and then we have this estimation, ~25% off from 0.7: |
| - | // 0.1/32 + 0.2/32 + 0.3/16 + 0.4/8 + 0.5/4 + 0.6/2 = 0.503125 |
| // +----- -----+ ^ 1/2 | |
| // | n-1 | | |
| @@ -472,8 +491,10 @@ filter_datapoints(peer_t *p, double t) | |
| sum = SQRT(sum) / NUM_DATAPOINTS; | |
| p->filter_jitter = sum > G_precision_sec ? sum : G_precision_sec; | |
| - | VERB3 bb_error_msg("filter offset:%f disp:%f jitter:%f", |
| - | p->filter_offset, p->filter_dispersion, p->filter_jitter); |
| + | VERB3 bb_error_msg("filter offset:%f(corr:%e) disp:%f jitter:%f", |
| + | p->filter_offset, x, |
| + | p->filter_dispersion, |
| + | p->filter_jitter); |
| } | |
| @@ -948,7 +969,7 @@ set_new_values(int disc_state, double offset, double recv_time) | |
| * of the last clock filter sample, which must be earlier than | |
| * the current time. | |
| */ | |
| - | VERB3 bb_error_msg("disc_state=%d last_update_offset=%f last_update_recv_time=%f", |
| + | VERB3 bb_error_msg("disc_state=%d last update offset=%f recv_time=%f", |
| disc_state, offset, recv_time); | |
| G.discipline_state = disc_state; | |
| G.last_update_offset = offset; | |
| @@ -1227,26 +1248,27 @@ update_local_clock(peer_t *p, double t) | |
| tmx.constant = G.poll_exp - 4; | |
| //tmx.esterror = (u_int32)(clock_jitter * 1e6); | |
| //tmx.maxerror = (u_int32)((sys_rootdelay / 2 + sys_rootdisp) * 1e6); | |
| - | VERB3 bb_error_msg("b adjtimex freq:%ld offset:%ld constant:%ld status:0x%x", |
| - | tmx.freq, tmx.offset, tmx.constant, tmx.status); |
| rc = adjtimex(&tmx); | |
| if (rc < 0) | |
| bb_perror_msg_and_die("adjtimex"); | |
| - | if (G.kernel_freq_drift != tmx.freq / 65536) { |
| - | G.kernel_freq_drift = tmx.freq / 65536; |
| - | VERB2 bb_error_msg("kernel clock drift: %ld ppm", G.kernel_freq_drift); |
| - | } |
| - | VERB3 { |
| - | bb_error_msg("adjtimex:%d freq:%ld offset:%ld constant:%ld status:0x%x", |
| + | /* 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 | |
| + | if (G.kernel_freq_drift != tmx.freq / 65536) { |
| + | G.kernel_freq_drift = tmx.freq / 65536; |
| + | VERB2 bb_error_msg("kernel clock drift: %ld ppm", G.kernel_freq_drift); |
| } | |
| // #define STA_MODE 0x4000 /* mode (0 = PLL, 1 = FLL) (ro) */ - ? | |
| // it appeared after a while: | |