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d3fe96027

Denys Vlasenko

2014-09-27

SUCCESS Duration: 143s

Subject

ntpd: be less eager to use shorter poll intervals

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Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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Commit Diff GitHub →

networking/ntpd.c +41 -39

networking/ntpd.c+41 -39

@@ -109,35 +109,43 @@
	* datapoints after the step.
	*/

-	#define RETRY_INTERVAL 5 /* on error, retry in N secs */
-	#define RESPONSE_INTERVAL 15 /* wait for reply up to N secs */
	#define INITIAL_SAMPLES 4 /* how many samples do we want for init */
	#define BAD_DELAY_GROWTH 4 /* drop packet if its delay grew by more than this */

-	/* Clock discipline parameters and constants */
+	#define RETRY_INTERVAL 32 /* on send/recv error, retry in N secs (need to be power of 2) */
+	#define NOREPLY_INTERVAL 512 /* sent, but got no reply: cap next query by this many seconds */
+	#define RESPONSE_INTERVAL 16 /* wait for reply up to N secs */

	/* Step threshold (sec). std ntpd uses 0.128.
-	* Using exact power of 2 (1/8) results in smaller code */
+	* 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 (!)) */
+	/* Stepout threshold (sec). std ntpd uses 900 (11 mins (!)) */
+	#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
+	* for this peer by this many seconds:
+	*/
+	#define BIGOFF (STEP_THRESHOLD * 8)
+	#define BIGOFF_INTERVAL (1 << 7) /* 128 s */
+
	#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 we got largish offset from a peer, cap next query interval
-	* for this peer by this many seconds:
-	*/
-	#define BIGOFF_INTERVAL (1 << 6)
-	/* 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 10 /* 2^10 sec ~= 17 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 STEP_THRESHOLD = 0.125, it means we try to sync more aggressively
-	* if offset increases over ~0.04 sec */
+	* if offset increases over ~0.04 sec
+	*/
	#define POLLDOWN_OFFSET (STEP_THRESHOLD / 3)
	#define MINDISP 0.01 /* minimum dispersion (sec) */
	#define MAXDISP 16 /* maximum dispersion (sec) */
@@ -972,6 +980,16 @@ step_time(double offset)
	}
	}

+	static void clamp_pollexp_and_set_MAXSTRAT(void)
+	{
+	if (G.poll_exp < MINPOLL)
+	G.poll_exp = MINPOLL;
+	if (G.poll_exp >= BIGPOLL)
+	G.poll_exp = BIGPOLL - 1;
+	G.polladj_count = 0;
+	G.stratum = MAXSTRAT;
+	}
+

	/*
	* Selection and clustering, and their helpers
@@ -1453,9 +1471,7 @@ update_local_clock(peer_t *p)
	exit(0);
	}

-	G.polladj_count = 0;
-	G.poll_exp = MINPOLL;
-	G.stratum = MAXSTRAT;
+	clamp_pollexp_and_set_MAXSTRAT();

	run_script("step", offset);

@@ -1654,28 +1670,16 @@ update_local_clock(peer_t *p)
	* (helpers first)
	*/
	static unsigned
-	retry_interval(void)
-	{
-	/* Local problem, want to retry soon */
-	unsigned interval, r;
-	interval = RETRY_INTERVAL;
-	r = rand();
-	interval += r % (unsigned)(RETRY_INTERVAL / 4);
-	VERB4 bb_error_msg("chose retry interval:%u", interval);
-	return interval;
-	}
-	static unsigned
-	poll_interval(int exponent)
+	poll_interval(int upper_bound)
	{
	unsigned interval, r, mask;
-	exponent = G.poll_exp + exponent;
-	if (exponent < 0)
-	exponent = 0;
-	interval = 1 << exponent;
+	interval = 1 << G.poll_exp;
+	if (interval > upper_bound)
+	interval = upper_bound;
	mask = ((interval-1) >> 4) \| 1;
	r = rand();
	interval += r & mask; /* ~ random(0..1) * interval/16 */
-	VERB4 bb_error_msg("chose poll interval:%u (poll_exp:%d exp:%d)", interval, G.poll_exp, exponent);
+	VERB4 bb_error_msg("chose poll interval:%u (poll_exp:%d)", interval, G.poll_exp);
	return interval;
	}
	static NOINLINE void
@@ -1741,7 +1745,7 @@ recv_and_process_peer_pkt(peer_t *p)
	\|\| errno == EAGAIN
	) {
	//TODO: always do this?
-	interval = retry_interval();
+	interval = poll_interval(RETRY_INTERVAL);
	goto set_next_and_ret;
	}
	xfunc_die();
@@ -1897,8 +1901,8 @@ recv_and_process_peer_pkt(peer_t *p)

	/* Decide when to send new query for this peer */
	pick_normal_interval:
-	interval = poll_interval(0);
-	if (fabs(offset) >= STEP_THRESHOLD * 8 && interval > BIGOFF_INTERVAL) {
+	interval = poll_interval(INT_MAX);
+	if (fabs(offset) >= BIGOFF && interval > BIGOFF_INTERVAL) {
	/* If we are synced, offsets are less than STEP_THRESHOLD,
	* or at the very least not much larger than it.
	* Now we see a largish one.
@@ -2248,7 +2252,7 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
	/* Timed out waiting for reply */
	close(p->p_fd);
	p->p_fd = -1;
-	timeout = poll_interval(-2); /* -2: try a bit sooner */
+	timeout = poll_interval(NOREPLY_INTERVAL);
	bb_error_msg("timed out waiting for %s, reach 0x%02x, next query in %us",
	p->p_dotted, p->reachable_bits, timeout);
	set_next(p, timeout);
@@ -2339,9 +2343,7 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
	goto have_reachable_peer;
	}
	/* No peer responded for last 8 packets, panic */
-	G.polladj_count = 0;
-	G.poll_exp = MINPOLL;
-	G.stratum = MAXSTRAT;
+	clamp_pollexp_and_set_MAXSTRAT();
	run_script("unsync", 0.0);
	have_reachable_peer: ;
	}