[git commit master] ntpd: disable frequency estimation code
Denys Vlasenko
vda.linux at googlemail.com
Sun Jan 17 00:05:58 UTC 2010
commit: http://git.busybox.net/busybox/commit/?id=5b9a910749176cabcd6e822ca46af66a9947d032
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master
function old new delta
reset_peer_stats 164 168 +4
ntp_init 371 368 -3
recv_and_process_peer_pkt 869 852 -17
update_local_clock 823 759 -64
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/3 up/down: 4/-84) Total: -80 bytes
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
networking/ntpd.c | 69 ++++++++++++++++++++++++++++++++++------------------
1 files changed, 45 insertions(+), 24 deletions(-)
diff --git a/networking/ntpd.c b/networking/ntpd.c
index e52d20c..b2cd0a3 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -57,6 +57,10 @@
* seconds. After WATCH_THRESHOLD seconds we look at accumulated
* offset and estimate frequency drift.
*
+ * (frequency measurement step seems to not be strictly needed,
+ * it is conditionally disabled with USING_INITIAL_FREQ_ESTIMATION
+ * define set to 0)
+ *
* After this, we enter "steady state": we collect a datapoint,
* we select the best peer, if this datapoint is not a new one
* (IOW: if this datapoint isn't for selected peer), sleep
@@ -76,21 +80,27 @@
#define INITIAL_SAMLPES 4 /* how many samples do we want for init */
/* Clock discipline parameters and constants */
-#define STEP_THRESHOLD 0.128 /* step threshold (s) */
-#define WATCH_THRESHOLD 150 /* stepout threshold (s). std ntpd uses 900 (11 mins (!)) */
+
+/* Step threshold (sec). std ntpd uses 0.128.
+ * Using exact power of 2 (1/8) results in smaller code */
+#define STEP_THRESHOLD 0.125
+#define WATCH_THRESHOLD 128 /* stepout threshold (sec). std ntpd uses 900 (11 mins (!)) */
/* NB: set WATCH_THRESHOLD to ~60 when debugging to save time) */
-//UNUSED: #define PANIC_THRESHOLD 1000 /* panic threshold (s) */
+//UNUSED: #define PANIC_THRESHOLD 1000 /* panic threshold (sec) */
#define FREQ_TOLERANCE 0.000015 /* frequency tolerance (15 PPM) */
#define BURSTPOLL 0 /* initial poll */
-#define MINPOLL 4 /* minimum poll interval (6: 64 s) */
+#define MINPOLL 5 /* minimum poll interval. std ntpd uses 6 (6: 64 sec) */
#define BIGPOLL 10 /* drop to lower poll at any trouble (10: 17 min) */
-#define MAXPOLL 12 /* maximum poll interval (12: 1.1h, 17: 36.4h) (was 17) */
-#define POLLDOWN_OFFSET (STEP_THRESHOLD / 3) /* actively lower poll when we see such big offsets */
-#define MINDISP 0.01 /* minimum dispersion (s) */
-#define MAXDISP 16 /* maximum dispersion (s) */
+#define MAXPOLL 12 /* maximum poll interval (12: 1.1h, 17: 36.4h). std ntpd uses 17 */
+/* Actively lower poll when we see such big offsets.
+ * With STEP_THRESHOLD = 0.125, it means we try to sync more aggressively
+ * if offset increases over 0.03 sec */
+#define POLLDOWN_OFFSET (STEP_THRESHOLD / 4)
+#define MINDISP 0.01 /* minimum dispersion (sec) */
+#define MAXDISP 16 /* maximum dispersion (sec) */
#define MAXSTRAT 16 /* maximum stratum (infinity metric) */
-#define MAXDIST 1 /* distance threshold (s) */
+#define MAXDIST 1 /* distance threshold (sec) */
#define MIN_SELECTED 1 /* minimum intersection survivors */
#define MIN_CLUSTERED 3 /* minimum cluster survivors */
@@ -109,7 +119,7 @@
* by staying at smaller poll).
*/
#define POLLADJ_GATE 4
-/* Compromise Allan intercept (s). doc uses 1500, std ntpd uses 512 */
+/* Compromise Allan intercept (sec). doc uses 1500, std ntpd uses 512 */
#define ALLAN 512
/* PLL loop gain */
#define PLL 65536
@@ -214,6 +224,9 @@ typedef struct {
} peer_t;
+#define USING_KERNEL_PLL_LOOP 1
+#define USING_INITIAL_FREQ_ESTIMATION 0
+
enum {
OPT_n = (1 << 0),
OPT_q = (1 << 1),
@@ -284,6 +297,11 @@ struct globals {
smallint adjtimex_was_done;
smallint initial_poll_complete;
+#define STATE_NSET 0 /* initial state, "nothing is set" */
+//#define STATE_FSET 1 /* frequency set from file */
+#define STATE_SPIK 2 /* spike detected */
+//#define STATE_FREQ 3 /* initial frequency */
+#define STATE_SYNC 4 /* clock synchronized (normal operation) */
uint8_t discipline_state; // doc calls it c.state
uint8_t poll_exp; // s.poll
int polladj_count; // c.count
@@ -292,7 +310,6 @@ struct globals {
double last_update_recv_time; // s.t
double discipline_jitter; // c.jitter
//TODO: add s.jitter - grep for it here and see clock_combine() in doc
-#define USING_KERNEL_PLL_LOOP 1
#if !USING_KERNEL_PLL_LOOP
double discipline_freq_drift; // c.freq
//TODO: conditionally calculate wander? it's used only for logging
@@ -581,8 +598,10 @@ static void
reset_peer_stats(peer_t *p, double offset)
{
int i;
+ bool small_ofs = fabs(offset) < 16 * STEP_THRESHOLD;
+
for (i = 0; i < NUM_DATAPOINTS; i++) {
- if (offset < 16 * STEP_THRESHOLD) {
+ if (small_ofs) {
p->filter_datapoint[i].d_recv_time -= offset;
if (p->filter_datapoint[i].d_offset != 0) {
p->filter_datapoint[i].d_offset -= offset;
@@ -593,7 +612,7 @@ reset_peer_stats(peer_t *p, double offset)
p->filter_datapoint[i].d_dispersion = MAXDISP;
}
}
- if (offset < 16 * STEP_THRESHOLD) {
+ if (small_ofs) {
p->lastpkt_recv_time -= offset;
} else {
p->reachable_bits = 0;
@@ -1105,12 +1124,6 @@ set_new_values(int disc_state, double offset, double recv_time)
G.last_update_offset = offset;
G.last_update_recv_time = recv_time;
}
-/* Clock state definitions */
-#define STATE_NSET 0 /* initial state, "nothing is set" */
-#define STATE_FSET 1 /* frequency set from file */
-#define STATE_SPIK 2 /* spike detected */
-#define STATE_FREQ 3 /* initial frequency */
-#define STATE_SYNC 4 /* clock synchronized (normal operation) */
/* Return: -1: decrease poll interval, 0: leave as is, 1: increase */
static NOINLINE int
update_local_clock(peer_t *p)
@@ -1156,6 +1169,7 @@ update_local_clock(peer_t *p)
#if !USING_KERNEL_PLL_LOOP
freq_drift = 0;
#endif
+#if USING_INITIAL_FREQ_ESTIMATION
if (G.discipline_state == STATE_FREQ) {
/* Ignore updates until the stepout threshold */
if (since_last_update < WATCH_THRESHOLD) {
@@ -1163,10 +1177,11 @@ update_local_clock(peer_t *p)
WATCH_THRESHOLD - since_last_update);
return 0; /* "leave poll interval as is" */
}
-#if !USING_KERNEL_PLL_LOOP
+# if !USING_KERNEL_PLL_LOOP
freq_drift = (offset - G.last_update_offset) / since_last_update;
-#endif
+# endif
}
+#endif
/* There are two main regimes: when the
* offset exceeds the step threshold and when it does not.
@@ -1225,10 +1240,12 @@ update_local_clock(peer_t *p)
run_script("step", offset);
+#if USING_INITIAL_FREQ_ESTIMATION
if (G.discipline_state == STATE_NSET) {
set_new_values(STATE_FREQ, /*offset:*/ 0, recv_time);
return 1; /* "ok to increase poll interval" */
}
+#endif
set_new_values(STATE_SYNC, /*offset:*/ 0, recv_time);
} else { /* abs_offset <= STEP_THRESHOLD */
@@ -1255,11 +1272,15 @@ update_local_clock(peer_t *p)
*/
exit(0);
}
+#if USING_INITIAL_FREQ_ESTIMATION
/* This is the first update received and the frequency
* has not been initialized. The first thing to do
* is directly measure the oscillator frequency.
*/
set_new_values(STATE_FREQ, offset, recv_time);
+#else
+ set_new_values(STATE_SYNC, offset, recv_time);
+#endif
VERB3 bb_error_msg("transitioning to FREQ, datapoint ignored");
return 0; /* "leave poll interval as is" */
@@ -1274,6 +1295,7 @@ update_local_clock(peer_t *p)
break;
#endif
+#if USING_INITIAL_FREQ_ESTIMATION
case STATE_FREQ:
/* since_last_update >= WATCH_THRESHOLD, we waited enough.
* Correct the phase and frequency and switch to SYNC state.
@@ -1281,6 +1303,7 @@ update_local_clock(peer_t *p)
*/
set_new_values(STATE_SYNC, offset, recv_time);
break;
+#endif
default:
#if !USING_KERNEL_PLL_LOOP
@@ -1579,9 +1602,7 @@ recv_and_process_peer_pkt(peer_t *p)
/* If drift is dangerously large, immediately
* drop poll interval one step down.
*/
- if (q->filter_offset < -POLLDOWN_OFFSET
- || q->filter_offset > POLLDOWN_OFFSET
- ) {
+ if (fabs(q->filter_offset) >= POLLDOWN_OFFSET) {
VERB3 bb_error_msg("offset:%f > POLLDOWN_OFFSET", q->filter_offset);
goto poll_down;
}
--
1.6.3.3
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