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ntpd: experimental code to correct frequency a bit more aggressively

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function                                             old     new   delta
update_local_clock                                   730     792     +62
recv_and_process_peer_pkt                            850     835     -15

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2012-03-05 00:51:48 +01:00
parent e8cfc3f693
commit 132b044f4b
1 changed files with 29 additions and 23 deletions
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52
networking/ntpd.c
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@ -138,6 +138,7 @@
* by staying at smaller poll). * by staying at smaller poll).
*/ */
#define POLLADJ_GATE 4 #define POLLADJ_GATE 4
#define TIMECONST_HACK_GATE 2
/* Compromise Allan intercept (sec). doc uses 1500, std ntpd uses 512 */ /* Compromise Allan intercept (sec). doc uses 1500, std ntpd uses 512 */
#define ALLAN 512 #define ALLAN 512
/* PLL loop gain */ /* PLL loop gain */
@ -339,6 +340,7 @@ struct globals {
double last_update_offset; // c.last double last_update_offset; // c.last
double last_update_recv_time; // s.t double last_update_recv_time; // s.t
double discipline_jitter; // c.jitter double discipline_jitter; // c.jitter
double offset_to_jitter_ratio;
//double cluster_offset; // s.offset //double cluster_offset; // s.offset
//double cluster_jitter; // s.jitter //double cluster_jitter; // s.jitter
#if !USING_KERNEL_PLL_LOOP #if !USING_KERNEL_PLL_LOOP
@ -1337,7 +1339,8 @@ update_local_clock(peer_t *p)
return 1; /* "ok to increase poll interval" */ return 1; /* "ok to increase poll interval" */
} }
#endif #endif
set_new_values(STATE_SYNC, /*offset:*/ 0, recv_time); offset = 0;
set_new_values(STATE_SYNC, offset, recv_time);
} else { /* abs_offset <= STEP_THRESHOLD */ } else { /* abs_offset <= STEP_THRESHOLD */
@ -1355,6 +1358,7 @@ update_local_clock(peer_t *p)
G.discipline_jitter = SQRT(etemp + (dtemp - etemp) / AVG); G.discipline_jitter = SQRT(etemp + (dtemp - etemp) / AVG);
if (G.discipline_jitter < G_precision_sec) if (G.discipline_jitter < G_precision_sec)
G.discipline_jitter = G_precision_sec; G.discipline_jitter = G_precision_sec;
G.offset_to_jitter_ratio = fabs(offset) / G.discipline_jitter;
VERB3 bb_error_msg("discipline jitter=%f", G.discipline_jitter); VERB3 bb_error_msg("discipline jitter=%f", G.discipline_jitter);
switch (G.discipline_state) { switch (G.discipline_state) {
@ -1443,7 +1447,7 @@ update_local_clock(peer_t *p)
/* We are in STATE_SYNC now, but did not do adjtimex yet. /* We are in STATE_SYNC now, but did not do adjtimex yet.
* (Any other state does not reach this, they all return earlier) * (Any other state does not reach this, they all return earlier)
* By this time, freq_drift and G.last_update_offset are set * By this time, freq_drift and offset are set
* to values suitable for adjtimex. * to values suitable for adjtimex.
*/ */
#if !USING_KERNEL_PLL_LOOP #if !USING_KERNEL_PLL_LOOP
@ -1482,40 +1486,42 @@ update_local_clock(peer_t *p)
tmx.modes = ADJ_FREQUENCY | ADJ_OFFSET; tmx.modes = ADJ_FREQUENCY | ADJ_OFFSET;
/* 65536 is one ppm */ /* 65536 is one ppm */
tmx.freq = G.discipline_freq_drift * 65536e6; tmx.freq = G.discipline_freq_drift * 65536e6;
tmx.offset = G.last_update_offset * 1000000; /* usec */
#endif #endif
tmx.modes = ADJ_OFFSET | ADJ_STATUS | ADJ_TIMECONST;// | ADJ_MAXERROR | ADJ_ESTERROR; tmx.modes = ADJ_OFFSET | ADJ_STATUS | ADJ_TIMECONST;// | ADJ_MAXERROR | ADJ_ESTERROR;
tmx.offset = (G.last_update_offset * 1000000); /* usec */ tmx.offset = (offset * 1000000); /* usec */
/* + (G.last_update_offset < 0 ? -0.5 : 0.5) - too small to bother */
tmx.status = STA_PLL; tmx.status = STA_PLL;
if (G.ntp_status & LI_PLUSSEC) if (G.ntp_status & LI_PLUSSEC)
tmx.status |= STA_INS; tmx.status |= STA_INS;
if (G.ntp_status & LI_MINUSSEC) if (G.ntp_status & LI_MINUSSEC)
tmx.status |= STA_DEL; tmx.status |= STA_DEL;
tmx.constant = G.poll_exp - 4; tmx.constant = G.poll_exp - 4;
//tmx.esterror = (u_int32)(clock_jitter * 1e6); /* EXPERIMENTAL.
//tmx.maxerror = (u_int32)((sys_rootdelay / 2 + sys_rootdisp) * 1e6); * The below if statement should be unnecessary, but...
* It looks like Linux kernel's PLL is far too gentle in changing
* tmx.freq in response to clock offset. Offset keeps growing
* and eventually we fall back to smaller poll intervals.
* We can make correction more agressive (about x2) by supplying
* PLL time constant which is one less than the real one.
* To be on a safe side, let's do it only if offset is significantly
* larger than jitter.
*/
if (tmx.constant > 0 && G.offset_to_jitter_ratio > TIMECONST_HACK_GATE)
tmx.constant--;
//tmx.esterror = (uint32_t)(clock_jitter * 1e6);
//tmx.maxerror = (uint32_t)((sys_rootdelay / 2 + sys_rootdisp) * 1e6);
rc = adjtimex(&tmx); rc = adjtimex(&tmx);
if (rc < 0) if (rc < 0)
bb_perror_msg_and_die("adjtimex"); bb_perror_msg_and_die("adjtimex");
/* NB: here kernel returns constant == G.poll_exp, not == G.poll_exp - 4. /* NB: here kernel returns constant == G.poll_exp, not == G.poll_exp - 4.
* Not sure why. Perhaps it is normal. * Not sure why. Perhaps it is normal.
*/ */
VERB3 bb_error_msg("adjtimex:%d freq:%ld offset:%+ld constant:%ld status:0x%x", VERB3 bb_error_msg("adjtimex:%d freq:%ld offset:%+ld status:0x%x",
rc, tmx.freq, tmx.offset, tmx.constant, tmx.status); rc, tmx.freq, tmx.offset, 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
G.kernel_freq_drift = tmx.freq / 65536; G.kernel_freq_drift = tmx.freq / 65536;
VERB2 bb_error_msg("update peer:%s, offset:%+f, jitter:%f, clock drift:%+.3f ppm", VERB2 bb_error_msg("update peer:%s, offset:%+f, jitter:%f, clock drift:%+.3f ppm, tc:%d",
p->p_dotted, G.last_update_offset, G.discipline_jitter, (double)tmx.freq / 65536); p->p_dotted, offset, G.discipline_jitter, (double)tmx.freq / 65536, (int)tmx.constant);
return 1; /* "ok to increase poll interval" */ return 1; /* "ok to increase poll interval" */
} }
@ -1651,7 +1657,7 @@ recv_and_process_peer_pkt(peer_t *p)
if (!p->reachable_bits) { if (!p->reachable_bits) {
/* 1st datapoint ever - replicate offset in every element */ /* 1st datapoint ever - replicate offset in every element */
int i; int i;
for (i = 1; i < NUM_DATAPOINTS; i++) { for (i = 0; i < NUM_DATAPOINTS; i++) {
p->filter_datapoint[i].d_offset = datapoint->d_offset; p->filter_datapoint[i].d_offset = datapoint->d_offset;
} }
} }
@ -1706,7 +1712,7 @@ recv_and_process_peer_pkt(peer_t *p)
? "grows" : "falls" ? "grows" : "falls"
); );
} }
if (rc > 0 && fabs(q->filter_offset) < POLLADJ_GATE * G.discipline_jitter) { if (rc > 0 && G.offset_to_jitter_ratio < POLLADJ_GATE) {
/* was += G.poll_exp but it is a bit /* was += G.poll_exp but it is a bit
* too optimistic for my taste at high poll_exp's */ * too optimistic for my taste at high poll_exp's */
G.polladj_count += MINPOLL; G.polladj_count += MINPOLL;