[git commit] ntpd: don't stay at short polling interval
Denys Vlasenko
vda.linux at googlemail.com
Thu Oct 2 15:24:34 UTC 2014
commit: http://git.busybox.net/busybox/commit/?id=b434ce70696879aad066fff67253e44e5f5b238e
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master
To avoid polling servers frequently slowly increase the interval up
to BIGPOLL when
- no replies are received from a peer
- no source can be selected
- peer claims to be unsynchronized (e.g. we are polling it too
frequently)
When recv() returns with an error, drop code to try to continue
on network errors: I'm not convinced those cases happen in real life.
function old new delta
recv_and_process_peer_pkt 919 838 -81
Signed-off-by: Miroslav Lichvar <mlichvar at redhat.com>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
networking/ntpd.c | 80 +++++++++++++++++++++++++++++++++++------------------
1 files changed, 53 insertions(+), 27 deletions(-)
diff --git a/networking/ntpd.c b/networking/ntpd.c
index b2b2791..838a367 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -136,17 +136,17 @@
#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,
- * then it is decreased _at once_. (If < 2^BIGPOLL, it will be decreased _eventually_).
+ * 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 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.
* With STEP_THRESHOLD = 0.125, it means we try to sync more aggressively
* 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 MAXDISP 16 /* maximum dispersion (sec) */
#define MAXSTRAT 16 /* maximum stratum (infinity metric) */
@@ -984,8 +984,8 @@ 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;
+ if (G.poll_exp > BIGPOLL)
+ G.poll_exp = BIGPOLL;
G.polladj_count = 0;
G.stratum = MAXSTRAT;
}
@@ -1682,7 +1682,7 @@ poll_interval(int upper_bound)
VERB4 bb_error_msg("chose poll interval:%u (poll_exp:%d)", interval, G.poll_exp);
return interval;
}
-static NOINLINE void
+static void
adjust_poll(int count)
{
G.polladj_count += count;
@@ -1693,7 +1693,7 @@ adjust_poll(int count)
VERB4 bb_error_msg("polladj: discipline_jitter:%f ++poll_exp=%d",
G.discipline_jitter, G.poll_exp);
}
- } else if (G.polladj_count < -POLLADJ_LIMIT || (count < 0 && G.poll_exp >= BIGPOLL)) {
+ } else if (G.polladj_count < -POLLADJ_LIMIT || (count < 0 && G.poll_exp > BIGPOLL)) {
G.polladj_count = 0;
if (G.poll_exp > MINPOLL) {
llist_t *item;
@@ -1736,19 +1736,23 @@ recv_and_process_peer_pkt(peer_t *p)
* ntp servers reply from their *other IP*.
* TODO: maybe we should check at least what we can: from.port == 123?
*/
+ recv_again:
size = recv(p->p_fd, &msg, sizeof(msg), MSG_DONTWAIT);
- if (size == -1) {
- bb_perror_msg("recv(%s) error", p->p_dotted);
- if (errno == EHOSTUNREACH || errno == EHOSTDOWN
- || errno == ENETUNREACH || errno == ENETDOWN
- || errno == ECONNREFUSED || errno == EADDRNOTAVAIL
- || errno == EAGAIN
- ) {
-//TODO: always do this?
- interval = poll_interval(RETRY_INTERVAL);
- goto set_next_and_ret;
- }
- xfunc_die();
+ if (size < 0) {
+ if (errno == EINTR)
+ /* Signal caught */
+ goto recv_again;
+ if (errno == EAGAIN)
+ /* There was no packet after all
+ * (poll() returning POLLIN for a fd
+ * is not a ironclad guarantee that data is there)
+ */
+ return;
+ /*
+ * If you need a different handling for a specific
+ * errno, always explain it in comment.
+ */
+ bb_perror_msg_and_die("recv(%s) error", p->p_dotted);
}
if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
@@ -1774,10 +1778,15 @@ recv_and_process_peer_pkt(peer_t *p)
|| msg.m_stratum == 0
|| msg.m_stratum > NTP_MAXSTRATUM
) {
-// TODO: stratum 0 responses may have commands in 32-bit m_refid field:
-// "DENY", "RSTR" - peer does not like us at all
-// "RATE" - peer is overloaded, reduce polling freq
bb_error_msg("reply from %s: peer is unsynced", p->p_dotted);
+ /*
+ * Stratum 0 responses may have commands in 32-bit m_refid field:
+ * "DENY", "RSTR" - peer does not like us at all,
+ * "RATE" - peer is overloaded, reduce polling freq.
+ * If poll interval is small, increase it.
+ */
+ if (G.poll_exp < BIGPOLL)
+ goto increase_interval;
goto pick_normal_interval;
}
@@ -1866,11 +1875,19 @@ recv_and_process_peer_pkt(peer_t *p)
/* Muck with statictics and update the clock */
filter_datapoints(p);
q = select_and_cluster();
- rc = -1;
+ rc = 0;
if (q) {
- rc = 0;
if (!(option_mask32 & OPT_w)) {
rc = update_local_clock(q);
+#if 0
+//Disabled this because there is a case where largish offsets
+//are unavoidable: if network round-trip delay is, say, ~0.6s,
+//error in offset estimation would be ~delay/2 ~= 0.3s.
+//Thus, offsets will be usually in -0.3...0.3s range.
+//In this case, this code would keep poll interval small,
+//but it won't be helping.
+//BIGOFF check below deals with a case of seeing multi-second offsets.
+
/* If drift is dangerously large, immediately
* drop poll interval one step down.
*/
@@ -1879,9 +1896,15 @@ recv_and_process_peer_pkt(peer_t *p)
adjust_poll(-POLLADJ_LIMIT * 3);
rc = 0;
}
+#endif
}
+ } else {
+ /* No peer selected.
+ * If poll interval is small, increase it.
+ */
+ if (G.poll_exp < BIGPOLL)
+ goto increase_interval;
}
- /* else: no peer selected, rc = -1: we want to poll more often */
if (rc != 0) {
/* Adjust the poll interval by comparing the current offset
@@ -1893,6 +1916,7 @@ recv_and_process_peer_pkt(peer_t *p)
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 */
+ increase_interval:
adjust_poll(MINPOLL);
} else {
adjust_poll(-G.poll_exp * 2);
@@ -1917,7 +1941,6 @@ recv_and_process_peer_pkt(peer_t *p)
interval = BIGOFF_INTERVAL;
}
- set_next_and_ret:
set_next(p, interval);
}
@@ -2252,6 +2275,9 @@ int ntpd_main(int argc UNUSED_PARAM, char **argv)
/* Timed out waiting for reply */
close(p->p_fd);
p->p_fd = -1;
+ /* If poll interval is small, increase it */
+ if (G.poll_exp < BIGPOLL)
+ adjust_poll(MINPOLL);
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);
More information about the busybox-cvs
mailing list