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ntpd: be less eager to use shorter poll intervals

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* on step, poll interval drops to 8.5 mins instead of 32 seconds
* on total loss of all replies (no replies from any peer
  for last 8 requests), also drop poll interval to 8.5 mins
  instead of 32 seconds
* on send abd recv errors, RETRY_INTERVAL is now 32 seconds,
  not 5 seconds
* on timing out listening to reply, instead of unconditional
  shortening poll interval by x4, clamp it to NOREPLY_INTERVAL
  (512 seconds)
* if a largish offset is seen, clamp nexp poll interval
  to 128 seconds, not 64 seconds

function                                             old     new   delta
clamp_pollexp_and_set_MAXSTRAT                         -      37     +37
recv_and_process_peer_pkt                            861     869      +8
poll_interval                                         52      48      -4
update_local_clock                                   762     752     -10
ntpd_main                                           1063    1050     -13
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/3 up/down: 45/-27)             Total: 18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2014-09-27 22:56:09 +02:00
parent 186b98a86f
commit d3fe960271
1 changed files with 41 additions and 39 deletions
Download Patch File Download Diff File Expand all files Collapse all files

80
networking/ntpd.c
View File

@@ -109,35 +109,43 @@
* datapoints after the step. * 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 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 */ #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. /* 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 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) */ /* NB: set WATCH_THRESHOLD to ~60 when debugging to save time) */
//UNUSED: #define PANIC_THRESHOLD 1000 /* panic threshold (sec) */ //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 FREQ_TOLERANCE 0.000015 /* frequency tolerance (15 PPM) */
#define BURSTPOLL 0 /* initial poll */ #define BURSTPOLL 0 /* initial poll */
#define MINPOLL 5 /* minimum poll interval. std ntpd uses 6 (6: 64 sec) */ #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: * If offset > discipline_jitter * POLLADJ_GATE, and poll interval is >= 2^BIGPOLL,
*/
#define BIGOFF_INTERVAL (1 << 6)
/* 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_). * then it is decreased _at once_. (If < 2^BIGPOLL, it will be decreased _eventually_).
*/ */
#define BIGPOLL 10 /* 2^10 sec ~= 17 min */ #define BIGPOLL 10 /* 2^10 sec ~= 17 min */
#define MAXPOLL 12 /* maximum poll interval (12: 1.1h, 17: 36.4h). std ntpd uses 17 */ #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 * 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 POLLDOWN_OFFSET (STEP_THRESHOLD / 3)
#define MINDISP 0.01 /* minimum dispersion (sec) */ #define MINDISP 0.01 /* minimum dispersion (sec) */
#define MAXDISP 16 /* maximum 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 * Selection and clustering, and their helpers
@@ -1453,9 +1471,7 @@ update_local_clock(peer_t *p)
exit(0); exit(0);
} }
G.polladj_count = 0; clamp_pollexp_and_set_MAXSTRAT();
G.poll_exp = MINPOLL;
G.stratum = MAXSTRAT;
run_script("step", offset); run_script("step", offset);
@@ -1654,28 +1670,16 @@ update_local_clock(peer_t *p)
* (helpers first) * (helpers first)
*/ */
static unsigned static unsigned
retry_interval(void) poll_interval(int upper_bound)
{
/* 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)
{ {
unsigned interval, r, mask; unsigned interval, r, mask;
exponent = G.poll_exp + exponent; interval = 1 << G.poll_exp;
if (exponent < 0) if (interval > upper_bound)
exponent = 0; interval = upper_bound;
interval = 1 << exponent;
mask = ((interval-1) >> 4) | 1; mask = ((interval-1) >> 4) | 1;
r = rand(); r = rand();
interval += r & mask; /* ~ random(0..1) * interval/16 */ 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; return interval;
} }
static NOINLINE void static NOINLINE void
@@ -1741,7 +1745,7 @@ recv_and_process_peer_pkt(peer_t *p)
|| errno == EAGAIN || errno == EAGAIN
) { ) {
//TODO: always do this? //TODO: always do this?
interval = retry_interval(); interval = poll_interval(RETRY_INTERVAL);
goto set_next_and_ret; goto set_next_and_ret;
} }
xfunc_die(); xfunc_die();
@@ -1897,8 +1901,8 @@ recv_and_process_peer_pkt(peer_t *p)
/* Decide when to send new query for this peer */ /* Decide when to send new query for this peer */
pick_normal_interval: pick_normal_interval:
interval = poll_interval(0); interval = poll_interval(INT_MAX);
if (fabs(offset) >= STEP_THRESHOLD * 8 && interval > BIGOFF_INTERVAL) { if (fabs(offset) >= BIGOFF && interval > BIGOFF_INTERVAL) {
/* If we are synced, offsets are less than STEP_THRESHOLD, /* If we are synced, offsets are less than STEP_THRESHOLD,
* or at the very least not much larger than it. * or at the very least not much larger than it.
* Now we see a largish one. * Now we see a largish one.
@@ -2248,7 +2252,7 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
/* Timed out waiting for reply */ /* Timed out waiting for reply */
close(p->p_fd); close(p->p_fd);
p->p_fd = -1; 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", bb_error_msg("timed out waiting for %s, reach 0x%02x, next query in %us",
p->p_dotted, p->reachable_bits, timeout); p->p_dotted, p->reachable_bits, timeout);
set_next(p, timeout); set_next(p, timeout);
@@ -2339,9 +2343,7 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
goto have_reachable_peer; goto have_reachable_peer;
} }
/* No peer responded for last 8 packets, panic */ /* No peer responded for last 8 packets, panic */
G.polladj_count = 0; clamp_pollexp_and_set_MAXSTRAT();
G.poll_exp = MINPOLL;
G.stratum = MAXSTRAT;
run_script("unsync", 0.0); run_script("unsync", 0.0);
have_reachable_peer: ; have_reachable_peer: ;
} }