2d48d9b1c
Denys Vlasenko
2021-03-02
Subject
ntpd: tweak comments
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networking/ntpd.c+9 -23
| @@ -127,24 +127,15 @@ | |
| */ | |
| #define MAX_VERBOSE 3 | |
| - | |
| /* High-level description of the algorithm: | |
| * | |
| * We start running with very small poll_exp, BURSTPOLL, | |
| * in order to quickly accumulate INITIAL_SAMPLES 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. |
| - | * |
| - | * (frequency measurement step seems to not be strictly needed, |
| - | * it is conditionally disabled with USING_INITIAL_FREQ_ESTIMATION |
| - | * define set to 0) |
| + | * than STEP_THRESHOLD, otherwise it isn't stepped. |
| * | |
| - | * After this, we enter "steady state": we collect a datapoint, |
| - | * we select the best peer, if this datapoint is not a new one |
| + | * Then poll_exp is set to MINPOLL, and 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, | |
| @@ -189,13 +180,10 @@ | |
| // ^^^^ used to be 0.125. | |
| // Since Linux 2.6.26 (circa 2006), kernel accepts (-0.5s, +0.5s) range | |
| - | /* Stepout threshold (sec). std ntpd uses 900 (11 mins (!)) */ |
| - | //UNUSED: #define WATCH_THRESHOLD 128 |
| - | /* NB: set WATCH_THRESHOLD to ~60 when debugging to save time) */ |
| - | //UNUSED: #define PANIC_THRESHOLD 1000 /* panic threshold (sec) */ |
| - | /* |
| - | * If we got |offset| > BIGOFF from a peer, cap next query interval |
| + | // #define PANIC_THRESHOLD 1000 /* panic threshold (sec) */ |
| + | |
| + | /* If we got |offset| > BIGOFF from a peer, cap next query interval |
| * for this peer by this many seconds: | |
| */ | |
| #define BIGOFF STEP_THRESHOLD | |
| @@ -204,18 +192,16 @@ | |
| #define FREQ_TOLERANCE 0.000015 /* frequency tolerance (15 PPM) */ | |
| #define BURSTPOLL 0 /* initial poll */ | |
| #define MINPOLL 5 /* minimum poll interval. std ntpd uses 6 (6: 64 sec) */ | |
| - | /* |
| - | * If offset > discipline_jitter * POLLADJ_GATE, and poll interval is > 2^BIGPOLL, |
| + | /* If offset > discipline_jitter * POLLADJ_GATE, and poll interval is > 2^BIGPOLL, |
| * then it is decreased _at once_. (If <= 2^BIGPOLL, it will be decreased _eventually_). | |
| */ | |
| #define BIGPOLL 9 /* 2^9 sec ~= 8.5 min */ | |
| #define MAXPOLL 12 /* maximum poll interval (12: 1.1h, 17: 36.4h). std ntpd uses 17 */ | |
| - | /* |
| - | * Actively lower poll when we see such big offsets. |
| + | /* Actively lower poll when we see such big offsets. |
| * With SLEW_THRESHOLD = 0.125, it means we try to sync more aggressively | |
| * if offset increases over ~0.04 sec | |
| */ | |
| - | //#define POLLDOWN_OFFSET (SLEW_THRESHOLD / 3) |
| + | // #define POLLDOWN_OFFSET (SLEW_THRESHOLD / 3) |
| #define MINDISP 0.01 /* minimum dispersion (sec) */ | |
| #define MAXDISP 16 /* maximum dispersion (sec) */ | |
| #define MAXSTRAT 16 /* maximum stratum (infinity metric) */ | |