d98dc92d6
Denys Vlasenko
2012-03-08
Subject
ntpd: drop offset averaging code
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networking/ntpd.c+60 -23
| @@ -212,8 +212,8 @@ typedef struct { | |
| } msg_t; | |
| typedef struct { | |
| - | double d_recv_time; |
| double d_offset; | |
| + | double d_recv_time; |
| double d_dispersion; | |
| } datapoint_t; | |
| @@ -517,23 +517,34 @@ static void | |
| filter_datapoints(peer_t *p) | |
| { | |
| int i, idx; | |
| + | double sum, wavg; |
| + | datapoint_t *fdp; |
| + | |
| + | #if 0 |
| + | /* Simulations have shown that use of *averaged* offset for p->filter_offset |
| + | * is in fact worse than simply using last received one: with large poll intervals |
| + | * (>= 2048) averaging code uses offset values which are outdated by hours, |
| + | * and time/frequency correction goes totally wrong when fed essentially bogus offsets. |
| + | */ |
| int got_newest; | |
| - | double minoff, maxoff, wavg, sum, w; |
| + | double minoff, maxoff, w; |
| 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; |
| + | fdp = p->filter_datapoint; |
| + | |
| + | minoff = maxoff = fdp[0].d_offset; |
| for (i = 1; i < NUM_DATAPOINTS; i++) { | |
| - | if (minoff > p->filter_datapoint[i].d_offset) |
| - | minoff = p->filter_datapoint[i].d_offset; |
| - | if (maxoff < p->filter_datapoint[i].d_offset) |
| - | maxoff = p->filter_datapoint[i].d_offset; |
| + | if (minoff > fdp[i].d_offset) |
| + | minoff = fdp[i].d_offset; |
| + | if (maxoff < fdp[i].d_offset) |
| + | maxoff = fdp[i].d_offset; |
| } | |
| - | idx = p->datapoint_idx; /* most recent datapoint */ |
| + | idx = p->datapoint_idx; /* most recent datapoint's index */ |
| /* Average offset: | |
| * Drop two outliers and take weighted average of the rest: | |
| * most_recent/2 + older1/4 + older2/8 ... + older5/32 + older6/32 | |
| @@ -555,24 +566,24 @@ filter_datapoints(peer_t *p) | |
| VERB4 { | |
| bb_error_msg("datapoint[%d]: off:%f disp:%f(%f) age:%f%s", | |
| i, | |
| - | p->filter_datapoint[idx].d_offset, |
| - | p->filter_datapoint[idx].d_dispersion, dispersion(&p->filter_datapoint[idx]), |
| - | G.cur_time - p->filter_datapoint[idx].d_recv_time, |
| - | (minoff == p->filter_datapoint[idx].d_offset || maxoff == p->filter_datapoint[idx].d_offset) |
| + | fdp[idx].d_offset, |
| + | fdp[idx].d_dispersion, dispersion(&fdp[idx]), |
| + | G.cur_time - fdp[idx].d_recv_time, |
| + | (minoff == fdp[idx].d_offset || maxoff == fdp[idx].d_offset) |
| ? " (outlier by offset)" : "" | |
| ); | |
| } | |
| - | sum += dispersion(&p->filter_datapoint[idx]) / (2 << i); |
| + | sum += dispersion(&fdp[idx]) / (2 << i); |
| - | if (minoff == p->filter_datapoint[idx].d_offset) { |
| + | if (minoff == fdp[idx].d_offset) { |
| minoff -= 1; /* so that we don't match it ever again */ | |
| } else | |
| - | if (maxoff == p->filter_datapoint[idx].d_offset) { |
| + | if (maxoff == fdp[idx].d_offset) { |
| maxoff += 1; | |
| } else { | |
| - | oldest_off = p->filter_datapoint[idx].d_offset; |
| - | oldest_age = G.cur_time - p->filter_datapoint[idx].d_recv_time; |
| + | oldest_off = fdp[idx].d_offset; |
| + | oldest_age = G.cur_time - fdp[idx].d_recv_time; |
| if (!got_newest) { | |
| got_newest = 1; | |
| newest_off = oldest_off; | |
| @@ -605,6 +616,32 @@ filter_datapoints(peer_t *p) | |
| } | |
| p->filter_offset = wavg; | |
| + | #else |
| + | |
| + | fdp = p->filter_datapoint; |
| + | idx = p->datapoint_idx; /* most recent datapoint's index */ |
| + | |
| + | /* filter_offset: simply use the most recent value */ |
| + | p->filter_offset = fdp[idx].d_offset; |
| + | |
| + | /* n-1 |
| + | * --- dispersion(i) |
| + | * filter_dispersion = \ ------------- |
| + | * / (i+1) |
| + | * --- 2 |
| + | * i=0 |
| + | */ |
| + | wavg = 0; |
| + | sum = 0; |
| + | for (i = 0; i < NUM_DATAPOINTS; i++) { |
| + | sum += dispersion(&fdp[idx]) / (2 << i); |
| + | wavg += fdp[idx].d_offset; |
| + | idx = (idx - 1) & (NUM_DATAPOINTS - 1); |
| + | } |
| + | wavg /= NUM_DATAPOINTS; |
| + | p->filter_dispersion = sum; |
| + | #endif |
| + | |
| /* +----- -----+ ^ 1/2 | |
| * | n-1 | | |
| * | --- | | |
| @@ -618,13 +655,13 @@ filter_datapoints(peer_t *p) | |
| */ | |
| sum = 0; | |
| for (i = 0; i < NUM_DATAPOINTS; i++) { | |
| - | sum += SQUARE(wavg - p->filter_datapoint[i].d_offset); |
| + | sum += SQUARE(wavg - fdp[i].d_offset); |
| } | |
| sum = SQRT(sum / NUM_DATAPOINTS); | |
| p->filter_jitter = sum > G_precision_sec ? sum : G_precision_sec; | |
| - | VERB3 bb_error_msg("filter offset:%+f(corr:%e) disp:%f jitter:%f", |
| - | p->filter_offset, x, |
| + | VERB3 bb_error_msg("filter offset:%+f disp:%f jitter:%f", |
| + | p->filter_offset, |
| p->filter_dispersion, | |
| p->filter_jitter); | |
| } | |
| @@ -1667,15 +1704,15 @@ recv_and_process_peer_pkt(peer_t *p) | |
| p->reachable_bits |= 1; | |
| if ((MAX_VERBOSE && G.verbose) || (option_mask32 & OPT_w)) { | |
| - | bb_error_msg("reply from:%s reach:0x%02x offset:%+f delay:%f status:0x%02x strat:%d refid:0x%08x rootdelay:%f", |
| + | bb_error_msg("reply from:%s offset:%+f delay:%f status:0x%02x strat:%d refid:0x%08x rootdelay:%f reach:0x%02x", |
| p->p_dotted, | |
| - | p->reachable_bits, |
| datapoint->d_offset, | |
| p->lastpkt_delay, | |
| p->lastpkt_status, | |
| p->lastpkt_stratum, | |
| p->lastpkt_refid, | |
| - | p->lastpkt_rootdelay |
| + | p->lastpkt_rootdelay, |
| + | p->reachable_bits |
| /* not shown: m_ppoll, m_precision_exp, m_rootdisp, | |
| * m_reftime, m_orgtime, m_rectime, m_xmttime | |
| */ | |