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ntpd: suppress in-kernel frequency correction in first 8 adjtimex calls

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In other words: try to correct initially existing clock offset first,
before assuming that our clock drifts.

function                                             old     new   delta
update_local_clock                                   826     834      +8
ntp_init                                             550     557      +7
filter_datapoints                                    179     173      -6
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 15/-6)               Total: 9 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2018-03-10 21:25:53 +01:00
parent 3293bc1469
commit 39dfb4de38
1 changed files with 33 additions and 11 deletions
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44
networking/ntpd.c
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@ -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;