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ntpd: drop offset averaging code

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function                                             old     new   delta
filter_datapoints                                    475     174    -301

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2012-03-08 03:27:49 +01:00
parent 4e3beb2e1d
commit d98dc92d6a
1 changed files with 60 additions and 23 deletions
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83
networking/ntpd.c
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@ -212,8 +212,8 @@ typedef struct {
} msg_t;
typedef struct {
double d_recv_time;
double d_offset;
double d_recv_time;
double d_dispersion;
} datapoint_t;
@ -517,23 +517,34 @@ static void
filter_datapoints(peer_t *p)
{
int i, idx;
double sum, wavg;
datapoint_t *fdp;
#if 0
/* Simulations have shown that use of *averaged* offset for p->filter_offset
* is in fact worse than simply using last received one: with large poll intervals
* (>= 2048) averaging code uses offset values which are outdated by hours,
* and time/frequency correction goes totally wrong when fed essentially bogus offsets.
*/
int got_newest;
double minoff, maxoff, wavg, sum, w;
double minoff, maxoff, w;
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;
fdp = p->filter_datapoint;
minoff = maxoff = fdp[0].d_offset;
for (i = 1; i < NUM_DATAPOINTS; i++) {
if (minoff > p->filter_datapoint[i].d_offset)
minoff = p->filter_datapoint[i].d_offset;
if (maxoff < p->filter_datapoint[i].d_offset)
maxoff = p->filter_datapoint[i].d_offset;
if (minoff > fdp[i].d_offset)
minoff = fdp[i].d_offset;
if (maxoff < fdp[i].d_offset)
maxoff = fdp[i].d_offset;
}
idx = p->datapoint_idx; /* most recent datapoint */
idx = p->datapoint_idx; /* most recent datapoint's index */
/* Average offset:
* Drop two outliers and take weighted average of the rest:
* most_recent/2 + older1/4 + older2/8 ... + older5/32 + older6/32
@ -555,24 +566,24 @@ filter_datapoints(peer_t *p)
VERB4 {
bb_error_msg("datapoint[%d]: off:%f disp:%f(%f) age:%f%s",
i,
p->filter_datapoint[idx].d_offset,
p->filter_datapoint[idx].d_dispersion, dispersion(&p->filter_datapoint[idx]),
G.cur_time - p->filter_datapoint[idx].d_recv_time,
(minoff == p->filter_datapoint[idx].d_offset || maxoff == p->filter_datapoint[idx].d_offset)
fdp[idx].d_offset,
fdp[idx].d_dispersion, dispersion(&fdp[idx]),
G.cur_time - fdp[idx].d_recv_time,
(minoff == fdp[idx].d_offset || maxoff == fdp[idx].d_offset)
? " (outlier by offset)" : ""
);
}
sum += dispersion(&p->filter_datapoint[idx]) / (2 << i);
sum += dispersion(&fdp[idx]) / (2 << i);
if (minoff == p->filter_datapoint[idx].d_offset) {
if (minoff == fdp[idx].d_offset) {
minoff -= 1; /* so that we don't match it ever again */
} else
if (maxoff == p->filter_datapoint[idx].d_offset) {
if (maxoff == fdp[idx].d_offset) {
maxoff += 1;
} else {
oldest_off = p->filter_datapoint[idx].d_offset;
oldest_age = G.cur_time - p->filter_datapoint[idx].d_recv_time;
oldest_off = fdp[idx].d_offset;
oldest_age = G.cur_time - fdp[idx].d_recv_time;
if (!got_newest) {
got_newest = 1;
newest_off = oldest_off;
@ -605,6 +616,32 @@ filter_datapoints(peer_t *p)
}
p->filter_offset = wavg;
#else
fdp = p->filter_datapoint;
idx = p->datapoint_idx; /* most recent datapoint's index */
/* filter_offset: simply use the most recent value */
p->filter_offset = fdp[idx].d_offset;
/* n-1
* --- dispersion(i)
* filter_dispersion = \ -------------
* / (i+1)
* --- 2
* i=0
*/
wavg = 0;
sum = 0;
for (i = 0; i < NUM_DATAPOINTS; i++) {
sum += dispersion(&fdp[idx]) / (2 << i);
wavg += fdp[idx].d_offset;
idx = (idx - 1) & (NUM_DATAPOINTS - 1);
}
wavg /= NUM_DATAPOINTS;
p->filter_dispersion = sum;
#endif
/* +----- -----+ ^ 1/2
* | n-1 |
* | --- |
@ -618,13 +655,13 @@ filter_datapoints(peer_t *p)
*/
sum = 0;
for (i = 0; i < NUM_DATAPOINTS; i++) {
sum += SQUARE(wavg - p->filter_datapoint[i].d_offset);
sum += SQUARE(wavg - fdp[i].d_offset);
}
sum = SQRT(sum / NUM_DATAPOINTS);
p->filter_jitter = sum > G_precision_sec ? sum : G_precision_sec;
VERB3 bb_error_msg("filter offset:%+f(corr:%e) disp:%f jitter:%f",
p->filter_offset, x,
VERB3 bb_error_msg("filter offset:%+f disp:%f jitter:%f",
p->filter_offset,
p->filter_dispersion,
p->filter_jitter);
}
@ -1667,15 +1704,15 @@ recv_and_process_peer_pkt(peer_t *p)
p->reachable_bits |= 1;
if ((MAX_VERBOSE && G.verbose) || (option_mask32 & OPT_w)) {
bb_error_msg("reply from:%s reach:0x%02x offset:%+f delay:%f status:0x%02x strat:%d refid:0x%08x rootdelay:%f",
bb_error_msg("reply from:%s offset:%+f delay:%f status:0x%02x strat:%d refid:0x%08x rootdelay:%f reach:0x%02x",
p->p_dotted,
p->reachable_bits,
datapoint->d_offset,
p->lastpkt_delay,
p->lastpkt_status,
p->lastpkt_stratum,
p->lastpkt_refid,
p->lastpkt_rootdelay
p->lastpkt_rootdelay,
p->reachable_bits
/* not shown: m_ppoll, m_precision_exp, m_rootdisp,
* m_reftime, m_orgtime, m_rectime, m_xmttime
*/