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clientlog: undo clock adjustments in updated TX timestamps

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When the server clock was updated between saving of the RX timestamp and
updating the TX timestamp, a client using interleaved mode with the four
timestamps which minimize error in measured delay (e.g. chrony) had the
server clock adjustment included in the measured delay, which could
disrupt the sample filtering and weighting.

Add a handler to track the slew epoch and remember the last offset. Undo
the adjustment in TX timestamps which have their RX timestamp in the
previous epoch to fix the delay observed by the clients.

If an unknown clock step is detected, drop all timestamps.
This commit is contained in:
Miroslav Lichvar
2021-10-25 17:00:28 +02:00
parent 189bf9c536
commit bc33e1cda1
4 changed files with 94 additions and 6 deletions
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50
clientlog.c
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@@ -38,6 +38,7 @@
#include "array.h"
#include "clientlog.h"
#include "conf.h"
#include "local.h"
#include "memory.h"
#include "ntp.h"
#include "reports.h"
@@ -125,7 +126,8 @@ static int active;
/* RX and TX timestamp saved for clients using interleaved mode */
typedef struct {
uint64_t rx_ts;
uint32_t flags;
uint16_t flags;
uint16_t slew_epoch;
int32_t tx_ts_offset;
} NtpTimestamps;
@@ -141,6 +143,8 @@ typedef struct {
uint32_t max_size;
uint32_t cached_index;
uint64_t cached_rx_ts;
uint16_t slew_epoch;
double slew_offset;
} NtpTimestampMap;
static NtpTimestampMap ntp_ts_map;
@@ -163,6 +167,8 @@ static uint32_t total_record_drops;
/* ================================================== */
static int expand_hashtable(void);
static void handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
double doffset, LCL_ChangeType change_type, void *anything);
/* ================================================== */
@@ -407,6 +413,10 @@ CLG_Initialise(void)
ntp_ts_map.max_size = 1U << (slots2 + SLOT_BITS);
ntp_ts_map.cached_index = 0;
ntp_ts_map.cached_rx_ts = 0ULL;
ntp_ts_map.slew_epoch = 0;
ntp_ts_map.slew_offset = 0.0;
LCL_AddParameterChangeHandler(handle_slew, NULL);
}
/* ================================================== */
@@ -420,6 +430,8 @@ CLG_Finalise(void)
ARR_DestroyInstance(records);
if (ntp_ts_map.timestamps)
ARR_DestroyInstance(ntp_ts_map.timestamps);
LCL_RemoveParameterChangeHandler(handle_slew, NULL);
}
/* ================================================== */
@@ -864,6 +876,7 @@ CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts)
tss = get_ntp_tss(index);
tss->rx_ts = rx;
tss->flags = 0;
tss->slew_epoch = ntp_ts_map.slew_epoch;
set_ntp_tx_offset(tss, rx_ts, tx_ts);
DEBUG_LOG("Saved RX+TX index=%"PRIu32" first=%"PRIu32" size=%"PRIu32,
@@ -872,6 +885,41 @@ CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts)
/* ================================================== */
static void
handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
double doffset, LCL_ChangeType change_type, void *anything)
{
/* Drop all timestamps on unknown step */
if (change_type == LCL_ChangeUnknownStep) {
ntp_ts_map.size = 0;
ntp_ts_map.cached_rx_ts = 0ULL;
}
ntp_ts_map.slew_epoch++;
ntp_ts_map.slew_offset = doffset;
}
/* ================================================== */
void
CLG_UndoNtpTxTimestampSlew(NTP_int64 *rx_ts, struct timespec *tx_ts)
{
uint32_t index;
if (!ntp_ts_map.timestamps)
return;
if (!find_ntp_rx_ts(ntp64_to_int64(rx_ts), &index))
return;
/* If the RX timestamp was captured before the last correction of the clock,
remove the adjustment from the TX timestamp */
if ((uint16_t)(get_ntp_tss(index)->slew_epoch + 1U) == ntp_ts_map.slew_epoch)
UTI_AddDoubleToTimespec(tx_ts, ntp_ts_map.slew_offset, tx_ts);
}
/* ================================================== */
void
CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts)
{