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authorDenys Vlasenko <vda.linux@googlemail.com>2012-03-04 23:51:48 (GMT)
committer Denys Vlasenko <vda.linux@googlemail.com>2012-03-04 23:51:48 (GMT)
commit132b044f4b09cd9334718b3f58dbb498ca63f82e (patch)
tree3ca56d757348a0048d06c3c042f174c60bd8dcaf
parente8cfc3f693e8a0cbfc489564c76e00c074f63066 (diff)
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ntpd: experimental code to correct frequency a bit more aggressively
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>
-rw-r--r--networking/ntpd.c52
1 files changed, 29 insertions, 23 deletions
diff --git a/networking/ntpd.c b/networking/ntpd.c
index ba666b5..b0bfe44 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -138,6 +138,7 @@
* by staying at smaller poll).
*/
#define POLLADJ_GATE 4
+#define TIMECONST_HACK_GATE 2
/* Compromise Allan intercept (sec). doc uses 1500, std ntpd uses 512 */
#define ALLAN 512
/* PLL loop gain */
@@ -339,6 +340,7 @@ struct globals {
double last_update_offset; // c.last
double last_update_recv_time; // s.t
double discipline_jitter; // c.jitter
+ double offset_to_jitter_ratio;
//double cluster_offset; // s.offset
//double cluster_jitter; // s.jitter
#if !USING_KERNEL_PLL_LOOP
@@ -1337,7 +1339,8 @@ update_local_clock(peer_t *p)
return 1; /* "ok to increase poll interval" */
}
#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 */
@@ -1355,6 +1358,7 @@ update_local_clock(peer_t *p)
G.discipline_jitter = SQRT(etemp + (dtemp - etemp) / AVG);
if (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);
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.
* (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.
*/
#if !USING_KERNEL_PLL_LOOP
@@ -1482,40 +1486,42 @@ update_local_clock(peer_t *p)
tmx.modes = ADJ_FREQUENCY | ADJ_OFFSET;
/* 65536 is one ppm */
tmx.freq = G.discipline_freq_drift * 65536e6;
- tmx.offset = G.last_update_offset * 1000000; /* usec */
#endif
tmx.modes = ADJ_OFFSET | ADJ_STATUS | ADJ_TIMECONST;// | ADJ_MAXERROR | ADJ_ESTERROR;
- tmx.offset = (G.last_update_offset * 1000000); /* usec */
- /* + (G.last_update_offset < 0 ? -0.5 : 0.5) - too small to bother */
+ tmx.offset = (offset * 1000000); /* usec */
tmx.status = STA_PLL;
if (G.ntp_status & LI_PLUSSEC)
tmx.status |= STA_INS;
if (G.ntp_status & LI_MINUSSEC)
tmx.status |= STA_DEL;
+
tmx.constant = G.poll_exp - 4;
- //tmx.esterror = (u_int32)(clock_jitter * 1e6);
- //tmx.maxerror = (u_int32)((sys_rootdelay / 2 + sys_rootdisp) * 1e6);
+ /* EXPERIMENTAL.
+ * 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);
if (rc < 0)
bb_perror_msg_and_die("adjtimex");
/* 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
+ VERB3 bb_error_msg("adjtimex:%d freq:%ld offset:%+ld status:0x%x",
+ rc, tmx.freq, tmx.offset, tmx.status);
G.kernel_freq_drift = tmx.freq / 65536;
- VERB2 bb_error_msg("update peer:%s, offset:%+f, jitter:%f, clock drift:%+.3f ppm",
- p->p_dotted, G.last_update_offset, G.discipline_jitter, (double)tmx.freq / 65536);
+ VERB2 bb_error_msg("update peer:%s, offset:%+f, jitter:%f, clock drift:%+.3f ppm, tc:%d",
+ p->p_dotted, offset, G.discipline_jitter, (double)tmx.freq / 65536, (int)tmx.constant);
return 1; /* "ok to increase poll interval" */
}
@@ -1651,7 +1657,7 @@ recv_and_process_peer_pkt(peer_t *p)
if (!p->reachable_bits) {
/* 1st datapoint ever - replicate offset in every element */
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;
}
}
@@ -1706,7 +1712,7 @@ recv_and_process_peer_pkt(peer_t *p)
? "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
* too optimistic for my taste at high poll_exp's */
G.polladj_count += MINPOLL;