ntpd: speed up resyncing if our clock is seriously off
function old new delta recv_and_process_peer_pkt 892 922 +30 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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@ -90,12 +90,24 @@
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* was hibernated, someone set totally wrong date, etc),
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* then the time is stepped, all datapoints are discarded,
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* and we go back to steady state.
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*
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* Made some changes to speed up re-syncing after our clock goes bad
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* (tested with suspending my laptop):
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* - if largish offset (>= STEP_THRESHOLD * 8 == 1 sec) is seen
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* from a peer, schedule next query for this peer soon
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* without drastically lowering poll interval for everybody.
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* This makes us collect enough data for step much faster:
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* e.g. at poll = 10 (1024 secs), step was done within 5 minutes
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* after first reply which indicated that our clock is 14 seconds off.
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* - on step, do not discard d_dispersion data of the existing datapoints,
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* do not clear reachable_bits. This prevents discarding first ~8
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* datapoints after the step.
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*/
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#define RETRY_INTERVAL 5 /* on error, retry in N secs */
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#define RETRY_INTERVAL 5 /* on error, retry in N secs */
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#define RESPONSE_INTERVAL 15 /* wait for reply up to N secs */
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#define INITIAL_SAMPLES 4 /* how many samples do we want for init */
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#define BAD_DELAY_GROWTH 4 /* drop packet if its delay grew by more than this */
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#define INITIAL_SAMPLES 4 /* how many samples do we want for init */
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#define BAD_DELAY_GROWTH 4 /* drop packet if its delay grew by more than this */
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/* Clock discipline parameters and constants */
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@ -109,6 +121,10 @@
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#define FREQ_TOLERANCE 0.000015 /* frequency tolerance (15 PPM) */
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#define BURSTPOLL 0 /* initial poll */
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#define MINPOLL 5 /* minimum poll interval. std ntpd uses 6 (6: 64 sec) */
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/* If we got largish offset from a peer, cap next query interval
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* for this peer by this many seconds:
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*/
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#define BIGOFF_INTERVAL (1 << 6)
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/* If offset > discipline_jitter * POLLADJ_GATE, and poll interval is >= 2^BIGPOLL,
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* then it is decreased _at once_. (If < 2^BIGPOLL, it will be decreased _eventually_).
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*/
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@ -1658,11 +1674,13 @@ recv_and_process_peer_pkt(peer_t *p)
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ssize_t size;
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msg_t msg;
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double T1, T2, T3, T4;
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double dv;
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double dv, offset;
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unsigned interval;
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datapoint_t *datapoint;
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peer_t *q;
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offset = 0;
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/* We can recvfrom here and check from.IP, but some multihomed
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* ntp servers reply from their *other IP*.
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* TODO: maybe we should check at least what we can: from.port == 123?
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@ -1766,13 +1784,13 @@ recv_and_process_peer_pkt(peer_t *p)
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p->datapoint_idx = p->reachable_bits ? (p->datapoint_idx + 1) % NUM_DATAPOINTS : 0;
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datapoint = &p->filter_datapoint[p->datapoint_idx];
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datapoint->d_recv_time = T4;
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datapoint->d_offset = ((T2 - T1) + (T3 - T4)) / 2;
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datapoint->d_offset = offset = ((T2 - T1) + (T3 - T4)) / 2;
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datapoint->d_dispersion = LOG2D(msg.m_precision_exp) + G_precision_sec;
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if (!p->reachable_bits) {
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/* 1st datapoint ever - replicate offset in every element */
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int i;
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for (i = 0; i < NUM_DATAPOINTS; i++) {
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p->filter_datapoint[i].d_offset = datapoint->d_offset;
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p->filter_datapoint[i].d_offset = offset;
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}
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}
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@ -1780,7 +1798,7 @@ recv_and_process_peer_pkt(peer_t *p)
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if ((MAX_VERBOSE && G.verbose) || (option_mask32 & OPT_w)) {
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bb_error_msg("reply from %s: offset:%+f delay:%f status:0x%02x strat:%d refid:0x%08x rootdelay:%f reach:0x%02x",
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p->p_dotted,
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datapoint->d_offset,
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offset,
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p->lastpkt_delay,
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p->lastpkt_status,
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p->lastpkt_stratum,
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@ -1865,6 +1883,20 @@ recv_and_process_peer_pkt(peer_t *p)
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/* Decide when to send new query for this peer */
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pick_normal_interval:
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interval = poll_interval(0);
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if (fabs(offset) >= STEP_THRESHOLD * 8 && interval > BIGOFF_INTERVAL) {
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/* If we are synced, offsets are less than STEP_THRESHOLD,
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* or at the very least not much larger than it.
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* Now we see a largish one.
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* Either this peer is feeling bad, or packet got corrupted,
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* or _our_ clock is wrong now and _all_ peers will show similar
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* largish offsets too.
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* I observed this with laptop suspend stopping clock.
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* In any case, it makes sense to make next request soonish:
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* cases 1 and 2: get a better datapoint,
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* case 3: allows to resync faster.
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*/
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interval = BIGOFF_INTERVAL;
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}
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set_next_and_ret:
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set_next(p, interval);
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