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ntpd: improve frequency filtering

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2010-01-02 00:36:43 +01:00
parent a9aaeda0e9
commit d9109e3b48
1 changed files with 44 additions and 22 deletions
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66
networking/ntpd.c
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@ -390,8 +390,13 @@ static void
filter_datapoints(peer_t *p, double t)
{
int i, idx;
int got_newest;
double minoff, maxoff, wavg, sum, w;
double x = x;
double x = x; /* for compiler */
double oldest_off = oldest_off;
double oldest_age = oldest_age;
double newest_off = newest_off;
double newest_age = newest_age;
minoff = maxoff = p->filter_datapoint[0].d_offset;
for (i = 1; i < NUM_DATAPOINTS; i++) {
@ -416,6 +421,7 @@ filter_datapoints(peer_t *p, double t)
// / (i+1)
// --- 2
// i=0
got_newest = 0;
sum = 0;
for (i = 0; i < NUM_DATAPOINTS; i++) {
VERB4 {
@ -437,23 +443,36 @@ filter_datapoints(peer_t *p, double t)
if (maxoff == p->filter_datapoint[idx].d_offset) {
maxoff += 1;
} else {
x = p->filter_datapoint[idx].d_offset * w;
oldest_off = p->filter_datapoint[idx].d_offset;
oldest_age = t - p->filter_datapoint[idx].d_recv_time;
if (!got_newest) {
got_newest = 1;
newest_off = oldest_off;
newest_age = oldest_age;
}
x = oldest_off * w;
wavg += x;
w /= 2;
}
idx = (idx - 1) & (NUM_DATAPOINTS - 1);
}
wavg += x; /* add another older6/64 to form older6/32 */
p->filter_offset = wavg;
p->filter_dispersion = sum;
//TODO: fix systematic underestimation with large poll intervals.
// Imagine that we still have a bit of uncorrected drift,
// and poll interval is big. Offsets form a progression:
// 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7, 0.7 is most recent.
// The algorithm above drops 0.0 and 0.7 as outliers,
// and then we have this estimation, ~25% off from 0.7:
// 0.1/32 + 0.2/32 + 0.3/16 + 0.4/8 + 0.5/4 + 0.6/2 = 0.503125
wavg += x; /* add another older6/64 to form older6/32 */
/* Fix systematic underestimation with large poll intervals.
* Imagine that we still have a bit of uncorrected drift,
* and poll interval is big (say, 100 sec). Offsets form a progression:
* 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 - 0.7 is most recent.
* The algorithm above drops 0.0 and 0.7 as outliers,
* and then we have this estimation, ~25% off from 0.7:
* 0.1/32 + 0.2/32 + 0.3/16 + 0.4/8 + 0.5/4 + 0.6/2 = 0.503125
*/
x = newest_age / (oldest_age - newest_age); /* in above example, 100 / (600 - 100) */
if (x < 1) {
x = (newest_off - oldest_off) * x; /* 0.5 * 100/500 = 0.1 */
wavg += x;
}
p->filter_offset = wavg;
// +----- -----+ ^ 1/2
// | n-1 |
@ -472,8 +491,10 @@ filter_datapoints(peer_t *p, double t)
sum = SQRT(sum) / NUM_DATAPOINTS;
p->filter_jitter = sum > G_precision_sec ? sum : G_precision_sec;
VERB3 bb_error_msg("filter offset:%f disp:%f jitter:%f",
p->filter_offset, p->filter_dispersion, p->filter_jitter);
VERB3 bb_error_msg("filter offset:%f(corr:%e) disp:%f jitter:%f",
p->filter_offset, x,
p->filter_dispersion,
p->filter_jitter);
}
@ -948,7 +969,7 @@ set_new_values(int disc_state, double offset, double recv_time)
* of the last clock filter sample, which must be earlier than
* the current time.
*/
VERB3 bb_error_msg("disc_state=%d last_update_offset=%f last_update_recv_time=%f",
VERB3 bb_error_msg("disc_state=%d last update offset=%f recv_time=%f",
disc_state, offset, recv_time);
G.discipline_state = disc_state;
G.last_update_offset = offset;
@ -1227,26 +1248,27 @@ update_local_clock(peer_t *p, double t)
tmx.constant = G.poll_exp - 4;
//tmx.esterror = (u_int32)(clock_jitter * 1e6);
//tmx.maxerror = (u_int32)((sys_rootdelay / 2 + sys_rootdisp) * 1e6);
VERB3 bb_error_msg("b adjtimex freq:%ld offset:%ld constant:%ld status:0x%x",
tmx.freq, tmx.offset, tmx.constant, tmx.status);
rc = adjtimex(&tmx);
if (rc < 0)
bb_perror_msg_and_die("adjtimex");
if (G.kernel_freq_drift != tmx.freq / 65536) {
G.kernel_freq_drift = tmx.freq / 65536;
VERB2 bb_error_msg("kernel clock drift: %ld ppm", G.kernel_freq_drift);
}
VERB3 {
bb_error_msg("adjtimex:%d freq:%ld offset:%ld constant:%ld status:0x%x",
/* NB: here kernel returns constant == G.poll_exp, not == G.poll_exp - 4.
* Not sure why. Perhaps it is normal.
*/
VERB3 bb_error_msg("adjtimex:%d freq:%ld offset:%ld constant:%ld status:0x%x",
rc, tmx.freq, tmx.offset, tmx.constant, tmx.status);
#if 0
VERB3 {
/* always gives the same output as above msg */
memset(&tmx, 0, sizeof(tmx));
if (adjtimex(&tmx) < 0)
bb_perror_msg_and_die("adjtimex");
VERB3 bb_error_msg("c adjtimex freq:%ld offset:%ld constant:%ld status:0x%x",
tmx.freq, tmx.offset, tmx.constant, tmx.status);
}
#endif
if (G.kernel_freq_drift != tmx.freq / 65536) {
G.kernel_freq_drift = tmx.freq / 65536;
VERB2 bb_error_msg("kernel clock drift: %ld ppm", G.kernel_freq_drift);
}
// #define STA_MODE 0x4000 /* mode (0 = PLL, 1 = FLL) (ro) */ - ?
// it appeared after a while: