39dfb4de3
Denys Vlasenko
2018-03-10
Subject
ntpd: suppress in-kernel frequency correction in first 8 adjtimex calls
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networking/ntpd.c+33 -11
| @@ -165,8 +165,12 @@ | |
| * Using exact power of 2 (1/8) results in smaller code | |
| */ | |
| #define SLEW_THRESHOLD 0.125 | |
| + | //^^^^^^^^^^^^^^^^^^^^^^^^^^ TODO: man adjtimex about tmx.offset: |
| + | // "Since Linux 2.6.26, the supplied value is clamped to the range (-0.5s, +0.5s)" |
| + | // - can use this larger value instead? |
| + | |
| /* Stepout threshold (sec). std ntpd uses 900 (11 mins (!)) */ | |
| - | #define WATCH_THRESHOLD 128 |
| + | //UNUSED: #define WATCH_THRESHOLD 128 |
| /* NB: set WATCH_THRESHOLD to ~60 when debugging to save time) */ | |
| //UNUSED: #define PANIC_THRESHOLD 1000 /* panic threshold (sec) */ | |
| @@ -419,6 +423,7 @@ struct globals { | |
| uint8_t discipline_state; // doc calls it c.state | |
| uint8_t poll_exp; // s.poll | |
| int polladj_count; // c.count | |
| + | int FREQHOLD_cnt; |
| long kernel_freq_drift; | |
| peer_t *last_update_peer; | |
| double last_update_offset; // c.last | |
| @@ -1034,6 +1039,7 @@ step_time(double offset) | |
| tval = tvn.tv_sec; | |
| strftime_YYYYMMDDHHMMSS(buf, sizeof(buf), &tval); | |
| bb_error_msg("setting time to %s.%06u (offset %+fs)", buf, (unsigned)tvn.tv_usec, offset); | |
| + | //maybe? G.FREQHOLD_cnt = 0; |
| /* Correct various fields which contain time-relative values: */ | |
| @@ -1709,6 +1715,28 @@ update_local_clock(peer_t *p) | |
| tmx.freq = G.discipline_freq_drift * 65536e6; | |
| #endif | |
| tmx.modes = ADJ_OFFSET | ADJ_STATUS | ADJ_TIMECONST;// | ADJ_MAXERROR | ADJ_ESTERROR; | |
| + | tmx.status = STA_PLL; |
| + | if (G.FREQHOLD_cnt != 0) { |
| + | G.FREQHOLD_cnt--; |
| + | /* man adjtimex on STA_FREQHOLD: |
| + | * "Normally adjustments made via ADJ_OFFSET result in dampened |
| + | * frequency adjustments also being made. |
| + | * This flag prevents the small frequency adjustment from being |
| + | * made when correcting for an ADJ_OFFSET value." |
| + | * |
| + | * Use this flag for a few first adjustments at the beginning |
| + | * of ntpd execution, otherwise even relatively small initial |
| + | * offset tend to cause largish changes to in-kernel tmx.freq. |
| + | * If ntpd was restarted due to e.g. switch to another network, |
| + | * this destroys already well-established tmx.freq value. |
| + | */ |
| + | tmx.status |= STA_FREQHOLD; |
| + | } |
| + | if (G.ntp_status & LI_PLUSSEC) |
| + | tmx.status |= STA_INS; |
| + | if (G.ntp_status & LI_MINUSSEC) |
| + | tmx.status |= STA_DEL; |
| + | |
| tmx.constant = (int)G.poll_exp - 4; | |
| /* EXPERIMENTAL. | |
| * The below if statement should be unnecessary, but... | |
| @@ -1722,25 +1750,18 @@ update_local_clock(peer_t *p) | |
| */ | |
| if (G.offset_to_jitter_ratio >= TIMECONST_HACK_GATE) | |
| tmx.constant--; | |
| + | if (tmx.constant < 0) |
| + | tmx.constant = 0; |
| + | |
| tmx.offset = (long)(offset * 1000000); /* usec */ | |
| if (SLEW_THRESHOLD < STEP_THRESHOLD) { | |
| if (tmx.offset > (long)(SLEW_THRESHOLD * 1000000)) { | |
| tmx.offset = (long)(SLEW_THRESHOLD * 1000000); | |
| - | tmx.constant--; |
| } | |
| if (tmx.offset < -(long)(SLEW_THRESHOLD * 1000000)) { | |
| tmx.offset = -(long)(SLEW_THRESHOLD * 1000000); | |
| - | tmx.constant--; |
| } | |
| } | |
| - | if (tmx.constant < 0) |
| - | tmx.constant = 0; |
| - | |
| - | tmx.status = STA_PLL; |
| - | if (G.ntp_status & LI_PLUSSEC) |
| - | tmx.status |= STA_INS; |
| - | if (G.ntp_status & LI_MINUSSEC) |
| - | tmx.status |= STA_DEL; |
| //tmx.esterror = (uint32_t)(clock_jitter * 1e6); | |
| //tmx.maxerror = (uint32_t)((sys_rootdelay / 2 + sys_rootdisp) * 1e6); | |
| @@ -2227,6 +2248,7 @@ static NOINLINE void ntp_init(char **argv) | |
| if (BURSTPOLL != 0) | |
| G.poll_exp = BURSTPOLL; /* speeds up initial sync */ | |
| G.last_script_run = G.reftime = G.last_update_recv_time = gettime1900d(); /* sets G.cur_time too */ | |
| + | G.FREQHOLD_cnt = 8; |
| /* Parse options */ | |
| peers = NULL; | |