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authorGravatar Denys Vlasenko <vda.linux@googlemail.com>2021-03-02 19:54:09 +0100
committerGravatar Denys Vlasenko <vda.linux@googlemail.com>2021-03-02 19:54:09 +0100
commit2d48d9b1cca7745a514f8cf770308ceb48edb195 (patch)
tree2f6a33027e414b390f3d9cd30afff3f58faf7728
parent2d6c175d9b8b0c8eedda2f9bcf1b96a8117ab441 (diff)
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ntpd: tweak comments
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--networking/ntpd.c32
1 files changed, 9 insertions, 23 deletions
diff --git a/networking/ntpd.c b/networking/ntpd.c
index caf5cc299..0f350fa6f 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -127,24 +127,15 @@
*/
#define MAX_VERBOSE 3
-
/* High-level description of the algorithm:
*
* We start running with very small poll_exp, BURSTPOLL,
* in order to quickly accumulate INITIAL_SAMPLES datapoints
* for each peer. Then, time is stepped if the offset is larger
- * than STEP_THRESHOLD, otherwise it isn't; anyway, we enlarge
- * poll_exp to MINPOLL and enter frequency measurement step:
- * we collect new datapoints but ignore them for WATCH_THRESHOLD
- * 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)
+ * than STEP_THRESHOLD, otherwise it isn't stepped.
*
- * After this, we enter "steady state": we collect a datapoint,
- * we select the best peer, if this datapoint is not a new one
+ * Then poll_exp is set to MINPOLL, and 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
* and collect another one; otherwise, use its offset to update
* frequency drift, if offset is somewhat large, reduce poll_exp,
@@ -189,13 +180,10 @@
// ^^^^ used to be 0.125.
// Since Linux 2.6.26 (circa 2006), kernel accepts (-0.5s, +0.5s) range
-/* Stepout threshold (sec). std ntpd uses 900 (11 mins (!)) */
-//UNUSED: #define WATCH_THRESHOLD 128
-/* NB: set WATCH_THRESHOLD to ~60 when debugging to save time) */
-//UNUSED: #define PANIC_THRESHOLD 1000 /* panic threshold (sec) */
-/*
- * If we got |offset| > BIGOFF from a peer, cap next query interval
+// #define PANIC_THRESHOLD 1000 /* panic threshold (sec) */
+
+/* If we got |offset| > BIGOFF from a peer, cap next query interval
* for this peer by this many seconds:
*/
#define BIGOFF STEP_THRESHOLD
@@ -204,18 +192,16 @@
#define FREQ_TOLERANCE 0.000015 /* frequency tolerance (15 PPM) */
#define BURSTPOLL 0 /* initial poll */
#define MINPOLL 5 /* minimum poll interval. std ntpd uses 6 (6: 64 sec) */
-/*
- * If offset > discipline_jitter * POLLADJ_GATE, and poll interval is > 2^BIGPOLL,
+/* If offset > discipline_jitter * POLLADJ_GATE, and poll interval is > 2^BIGPOLL,
* then it is decreased _at once_. (If <= 2^BIGPOLL, it will be decreased _eventually_).
*/
#define BIGPOLL 9 /* 2^9 sec ~= 8.5 min */
#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.
+/* Actively lower poll when we see such big offsets.
* With SLEW_THRESHOLD = 0.125, it means we try to sync more aggressively
* if offset increases over ~0.04 sec
*/
-//#define POLLDOWN_OFFSET (SLEW_THRESHOLD / 3)
+// #define POLLDOWN_OFFSET (SLEW_THRESHOLD / 3)
#define MINDISP 0.01 /* minimum dispersion (sec) */
#define MAXDISP 16 /* maximum dispersion (sec) */
#define MAXSTRAT 16 /* maximum stratum (infinity metric) */