e4844b8a5
Denys Vlasenko
2010-01-01
Subject
ntpd: add a comment, no code changes
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networking/ntpd.c+8 -1
| @@ -432,7 +432,7 @@ filter_datapoints(peer_t *p, double t) | |
| sum += dispersion(&p->filter_datapoint[idx], t) / (2 << i); | |
| if (minoff == p->filter_datapoint[idx].d_offset) { | |
| - | minoff -= 1; |
| + | minoff -= 1; /* so that we don't match it ever again */ |
| } else | |
| if (maxoff == p->filter_datapoint[idx].d_offset) { | |
| maxoff += 1; | |
| @@ -447,6 +447,13 @@ filter_datapoints(peer_t *p, double t) | |
| 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 |
| // +----- -----+ ^ 1/2 | |
| // | n-1 | | |