9b1c8bf89
Denys Vlasenko
2018-08-03
Subject
ntpd: show real, unclamped delays on low-latency networks
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networking/ntpd.c+17 -14
| @@ -150,7 +150,7 @@ | |
| #define INITIAL_SAMPLES 4 /* how many samples do we want for init */ | |
| #define MIN_FREQHOLD 12 /* adjust offset, but not freq in this many first adjustments */ | |
| - | #define BAD_DELAY_GROWTH 4 /* drop packet if its delay grew by more than this */ |
| + | #define BAD_DELAY_GROWTH 4 /* drop packet if its delay grew by more than this factor */ |
| #define RETRY_INTERVAL 32 /* on send/recv error, retry in N secs (need to be power of 2) */ | |
| #define NOREPLY_INTERVAL 512 /* sent, but got no reply: cap next query by this many seconds */ | |
| @@ -1819,7 +1819,7 @@ update_local_clock(peer_t *p) | |
| VERB2 bb_error_msg("update from:%s offset:%+f delay:%f jitter:%f clock drift:%+.3fppm tc:%d", | |
| p->p_dotted, | |
| offset, | |
| - | p->lastpkt_delay, |
| + | p->p_raw_delay, |
| G.discipline_jitter, | |
| (double)tmx.freq / 65536, | |
| (int)tmx.constant | |
| @@ -1976,27 +1976,30 @@ recv_and_process_peer_pkt(peer_t *p) | |
| T2 = lfp_to_d(msg.m_rectime); | |
| T3 = lfp_to_d(msg.m_xmttime); | |
| T4 = G.cur_time; | |
| - | |
| - | /* The delay calculation is a special case. In cases where the |
| - | * server and client clocks are running at different rates and |
| - | * with very fast networks, the delay can appear negative. In |
| - | * order to avoid violating the Principle of Least Astonishment, |
| - | * the delay is clamped not less than the system precision. |
| - | */ |
| delay = (T4 - T1) - (T3 - T2); | |
| - | if (delay < G_precision_sec) |
| - | delay = G_precision_sec; |
| + | |
| /* | |
| * If this packet's delay is much bigger than the last one, | |
| * it's better to just ignore it than use its much less precise value. | |
| */ | |
| prev_delay = p->p_raw_delay; | |
| - | p->p_raw_delay = delay; |
| - | if (p->reachable_bits && delay > prev_delay * BAD_DELAY_GROWTH) { |
| + | p->p_raw_delay = (delay < 0 ? 0.0 : delay); |
| + | if (p->reachable_bits |
| + | && delay > prev_delay * BAD_DELAY_GROWTH |
| + | && delay > 1.0 / (8 * 1024) /* larger than ~0.000122 */ |
| + | ) { |
| bb_error_msg("reply from %s: delay %f is too high, ignoring", p->p_dotted, delay); | |
| goto pick_normal_interval; | |
| } | |
| + | /* The delay calculation is a special case. In cases where the |
| + | * server and client clocks are running at different rates and |
| + | * with very fast networks, the delay can appear negative. In |
| + | * order to avoid violating the Principle of Least Astonishment, |
| + | * the delay is clamped not less than the system precision. |
| + | */ |
| + | if (delay < G_precision_sec) |
| + | delay = G_precision_sec; |
| p->lastpkt_delay = delay; | |
| p->lastpkt_recv_time = T4; | |
| VERB6 bb_error_msg("%s->lastpkt_recv_time=%f", p->p_dotted, p->lastpkt_recv_time); | |
| @@ -2024,7 +2027,7 @@ recv_and_process_peer_pkt(peer_t *p) | |
| 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, | |
| offset, | |
| - | p->lastpkt_delay, |
| + | p->p_raw_delay, |
| p->lastpkt_status, | |
| p->lastpkt_stratum, | |
| p->lastpkt_refid, | |