diff options
| -rw-r--r-- | networking/ntpd.c | 39 |
1 files changed, 34 insertions, 5 deletions
diff --git a/networking/ntpd.c b/networking/ntpd.c index 092c444..e52d20c 100644 --- a/networking/ntpd.c +++ b/networking/ntpd.c @@ -46,8 +46,34 @@ #define MAX_VERBOSE 2 +/* High-level description of the algorithm: + * + * We start running with very small poll_exp, BURSTPOLL, + * in order to quickly accumulate INITIAL_SAMLPES datapoints + * for each peer. Then, time is stepped if the offset is larger + * than STEP_THRESHOLD, otherwise it isn't; anyway, we enlarge + * poll_exp to MINPOLL and enter frequency measurement step: + * we collect new datapoints but ignore them for WATCH_THRESHOLD + * seconds. After WATCH_THRESHOLD seconds we look at accumulated + * offset and estimate frequency drift. + * + * After this, we enter "steady state": we collect a datapoint, + * we select the best peer, if this datapoint is not a new one + * (IOW: if this datapoint isn't for selected peer), sleep + * and collect another one; otherwise, use its offset to update + * frequency drift, if offset is somewhat large, reduce poll_exp, + * otherwise increase poll_exp. + * + * If offset is larger than STEP_THRESHOLD, which shouldn't normally + * happen, we assume that something "bad" happened (computer + * was hibernated, someone set totally wrong date, etc), + * then the time is stepped, all datapoints are discarded, + * and we go back to steady state. + */ + #define RETRY_INTERVAL 5 /* on error, retry in N secs */ #define RESPONSE_INTERVAL 15 /* wait for reply up to N secs */ +#define INITIAL_SAMLPES 4 /* how many samples do we want for init */ /* Clock discipline parameters and constants */ #define STEP_THRESHOLD 0.128 /* step threshold (s) */ @@ -75,8 +101,9 @@ * we grow a counter: += MINPOLL. When it goes over POLLADJ_LIMIT, * we poll_exp++. If offset isn't small, counter -= poll_exp*2, * and when it goes below -POLLADJ_LIMIT, we poll_exp-- + * (bumped from 30 to 36 since otherwise I often see poll_exp going *2* steps down) */ -#define POLLADJ_LIMIT 30 +#define POLLADJ_LIMIT 36 /* If offset < POLLADJ_GATE * discipline_jitter, then we can increase * poll interval (we think we can't improve timekeeping * by staying at smaller poll). @@ -1555,6 +1582,7 @@ recv_and_process_peer_pkt(peer_t *p) if (q->filter_offset < -POLLDOWN_OFFSET || q->filter_offset > POLLDOWN_OFFSET ) { + VERB3 bb_error_msg("offset:%f > POLLDOWN_OFFSET", q->filter_offset); goto poll_down; } } @@ -1856,13 +1884,14 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv) idx2peer = xzalloc(sizeof(idx2peer[0]) * cnt); pfd = xzalloc(sizeof(pfd[0]) * cnt); - /* Countdown: we never sync before we sent 5 packets to each peer + /* Countdown: we never sync before we sent INITIAL_SAMLPES+1 + * packets to each peer. * NB: if some peer is not responding, we may end up sending * fewer packets to it and more to other peers. - * NB2: sync usually happens using 5-1=4 packets, since last reply - * does not come back instantaneously. + * NB2: sync usually happens using INITIAL_SAMLPES packets, + * since last reply does not come back instantaneously. */ - cnt = G.peer_cnt * 5; + cnt = G.peer_cnt * (INITIAL_SAMLPES + 1); while (!bb_got_signal) { llist_t *item; |