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conf: add clockprecision directive

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Make the precision of the system clock configurable. This can be useful
on servers using hardware timestamping to reduce the amount of noise
added to the NTP timestamps and improve stability of NTP measurements.
This commit is contained in:
Miroslav Lichvar
2020-09-01 11:21:46 +02:00
parent 9ca250755f
commit b7c7c293e5
4 changed files with 46 additions and 15 deletions
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28
local.c
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@@ -108,8 +108,8 @@ static double max_clock_error;
#define NSEC_PER_SEC 1000000000
static void
calculate_sys_precision(void)
static double
measure_clock_precision(void)
{
struct timespec ts, old_ts;
int iters, diff, best;
@@ -135,18 +135,7 @@ calculate_sys_precision(void)
assert(best > 0);
precision_quantum = 1.0e-9 * best;
/* Get rounded log2 value of the measured precision */
precision_log = 0;
while (best < 707106781) {
precision_log--;
best *= 2;
}
assert(precision_log >= -30);
DEBUG_LOG("Clock precision %.9f (%d)", precision_quantum, precision_log);
return 1.0e-9 * best;
}
/* ================================================== */
@@ -170,7 +159,16 @@ LCL_Initialise(void)
current_freq_ppm = 0.0;
temp_comp_ppm = 0.0;
calculate_sys_precision();
precision_quantum = CNF_GetClockPrecision();
if (precision_quantum <= 0.0)
precision_quantum = measure_clock_precision();
precision_quantum = CLAMP(1.0e-9, precision_quantum, 1.0);
precision_log = round(log(precision_quantum) / log(2.0));
/* NTP code doesn't support smaller log than -30 */
assert(precision_log >= -30);
DEBUG_LOG("Clock precision %.9f (%d)", precision_quantum, precision_log);
/* This is the maximum allowed frequency offset in ppm, the time must
never stop or run backwards */