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authorDenys Vlasenko <vda.linux@googlemail.com>2010-01-01 23:36:43 (GMT)
committer Denys Vlasenko <vda.linux@googlemail.com>2010-01-01 23:36:43 (GMT)
commitd9109e3b48d2eb2eebcc433bfa4d04a653a93d9b (patch)
tree11477a2190f04831338585126984ca6fafb9de47
parenta9aaeda0e9714eec74894734b30b6f5a45c97a48 (diff)
downloadbusybox-d9109e3b48d2eb2eebcc433bfa4d04a653a93d9b.tar.gz
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ntpd: improve frequency filtering
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--networking/ntpd.c64
1 files changed, 43 insertions, 21 deletions
diff --git a/networking/ntpd.c b/networking/ntpd.c
index 5431b74..5cad738 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -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);
}
+ p->filter_dispersion = sum;
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;
- 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
// +----- -----+ ^ 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: