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Improve peer polling in symmetric mode

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If the remote stratum is higher than ours, try to lock on the peer's
polling to minimize our response time by slightly extending our delay or
waiting for the peer to catch up with us as the random part in the
actual interval is reduced. If the remote stratum is equal to ours, try
to interleave evenly with the peer.
This commit is contained in:
Miroslav Lichvar 2013-06-04 19:20:37 +02:00
parent 288043c13b
commit cce7a5f15e
1 changed files with 20 additions and 1 deletions
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21
ntp_core.c
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@ -84,6 +84,8 @@ struct NCR_Instance_Record {
int local_poll; /* Log2 of polling interval at our end */
int remote_poll; /* Log2 of server/peer's polling interval (recovered
from received packets) */
int remote_stratum; /* Stratum of the server/peer (recovered from
received packets) */
int presend_minpoll; /* If the current polling interval is
at least this, an echo datagram
@ -178,6 +180,9 @@ struct NCR_Instance_Record {
/* Randomness added to spacing between samples for one server/peer */
#define SAMPLING_RANDOMNESS 0.02
/* Adjustment of the peer polling interval */
#define PEER_SAMPLING_ADJ 1.1
/* Spacing between samples in burst mode for one server/peer */
#define BURST_INTERVAL 2.0
@ -331,6 +336,7 @@ NCR_GetInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourcePar
result->local_poll = params->minpoll;
result->remote_poll = 0;
result->remote_stratum = 0;
/* Create a source instance for this NTP source */
result->source = SRC_CreateNewInstance(UTI_IPToRefid(&remote_addr->ip_addr), SRC_NTP, params->sel_option, &result->remote_addr.ip_addr);
@ -441,7 +447,7 @@ get_poll_adj(NCR_Instance inst, double error_in_estimate, double peer_distance)
static double
get_transmit_delay(NCR_Instance inst, int on_tx, double last_tx)
{
int poll_to_use;
int poll_to_use, stratum_diff;
double delay_time;
/* If we're in burst mode, queue for immediate dispatch.
@ -488,6 +494,18 @@ get_transmit_delay(NCR_Instance inst, int on_tx, double last_tx)
delay_time = (double) (1UL<<poll_to_use);
/* If the remote stratum is higher than ours, try to lock on the
peer's polling to minimize our response time by slightly extending
our delay or waiting for the peer to catch up with us as the
random part in the actual interval is reduced. If the remote
stratum is equal to ours, try to interleave evenly with the peer. */
stratum_diff = inst->remote_stratum - REF_GetOurStratum();
if ((stratum_diff > 0 && last_tx * PEER_SAMPLING_ADJ < delay_time) ||
(!on_tx && !stratum_diff &&
last_tx / delay_time > PEER_SAMPLING_ADJ - 0.5))
delay_time *= PEER_SAMPLING_ADJ;
/* Substract the already spend time */
if (last_tx > 0.0)
delay_time -= last_tx;
if (delay_time < 0.0)
@ -1116,6 +1134,7 @@ receive_packet(NTP_Packet *message, struct timeval *now, double now_err, NCR_Ins
if (valid_header && valid_data) {
inst->remote_poll = message->poll;
inst->remote_stratum = message->stratum;
inst->tx_count = 0;
SRC_UpdateReachability(inst->source, 1);