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Add test for ratio of increase in delay to stddev

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Require that the ratio of the increase in delay from the minimum one in
the stats data register to the standard deviation of the offsets in the
register is less than maxdelaydevratio or the difference between
measured offset and predicted offset is larger than the increase in
delay. In the allowed delay increase is included also skew and maximum
clock frequency error.

maxdelaydevratio is 10.0 by default.
This commit is contained in:
Miroslav Lichvar
2010-12-03 18:35:33 +01:00
parent feb8811f37
commit b977c95be4
12 changed files with 112 additions and 9 deletions
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39
sourcestats.c
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@@ -693,6 +693,45 @@ SST_MinRoundTripDelay(SST_Stats inst)
return inst->peer_delays[inst->min_delay_sample];
}
/* ================================================== */
int
SST_IsGoodSample(SST_Stats inst, double offset, double delay,
double max_delay_dev_ratio, double clock_error, struct timeval *when)
{
double elapsed, allowed_increase, delay_increase;
if (inst->n_samples < 3)
return 1;
UTI_DiffTimevalsToDouble(&elapsed, when, &inst->offset_time);
/* Require that the ratio of the increase in delay from the minimum to the
standard deviation is less than max_delay_dev_ratio. In the allowed
increase in delay include also skew and clock_error. */
allowed_increase = sqrt(inst->variance) * max_delay_dev_ratio +
elapsed * (inst->skew + clock_error);
delay_increase = (delay - SST_MinRoundTripDelay(inst)) / 2.0;
if (delay_increase < allowed_increase)
return 1;
offset -= inst->estimated_offset + elapsed * inst->estimated_frequency;
/* Before we decide to drop the sample, make sure the difference between
measured offset and predicted offset is not significantly larger than
the increase in delay */
if (fabs(offset) - delay_increase > allowed_increase)
return 1;
#if 0
LOG(LOGS_INFO, LOGF_SourceStats, "bad sample: offset=%f delay=%f incr_delay=%f allowed=%f", offset, delay, allowed_increase, delay_increase);
#endif
return 0;
}
/* ================================================== */
/* This is used to save the register to a file, so that we can reload
it after restarting the daemon */