servo: discard some clear outliers

This commit makes the servo engine discard events where "one way delay" is over one second (this will be documented). The management was never tested and likely wrong anyways. It also ignores events where the trip time appears to be negative. In this case the calculation is brought forward with the current value for one way delay (the current average). This happens when the slave is running a faster clock than the master during recovery. Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

servo: discard some clear outliers
This commit makes the servo engine discard events where "one way delay" is over one second (this will be documented). The management was never tested and likely wrong anyways. It also ignores events where the trip time appears to be negative. In this case the calculation is brought forward with the current value for one way delay (the current average). This happens when the slave is running a faster clock than the master during recovery. Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
47b6baab · Alessandro Rubini · a79b0d7f · 47b6baab
Commit 47b6baab authored Sep 15, 2013 by Alessandro Rubini
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Showing with 17 additions and 10 deletions

servo.c proto-standard/servo.c +17 -10

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--- a/proto-standard/servo.c
+++ b/proto-standard/servo.c
@@ -58,6 +58,11 @@ static int pp_servo_bad_event(struct pp_instance *ppi)
 {
 	TimeInternal *m_to_s_dly = &SRV(ppi)->m_to_s_dly;
 	TimeInternal *s_to_m_dly = &SRV(ppi)->s_to_m_dly;
+	TimeInternal *owd = &DSCUR(ppi)->oneWayDelay;
+
+	/* Discard one-way delays that overflow a second (makes no sense) */
+	if (owd->seconds)
+		return 1;

 	if (OPTS(ppi)->max_dly) { /* If maxDelay is 0 then it's OFF */
 		if (m_to_s_dly->seconds || s_to_m_dly->seconds) {
@@ -114,11 +119,14 @@ void pp_servo_got_resp(struct pp_instance *ppi)
 	if(pp_servo_bad_event(ppi))
 		return;

-	if (owd->seconds) {
-		/* cannot filter with secs, clear filter */
-		owd_fltr->s_exp = 0;
-		owd_fltr->nsec_prev = 0;
-	} else {
+	/*
+	 * It may happen that owd appears as negative. This happens when
+	 * the slave clock is running fast to recover a late time: the
+	 * (t3 - t2) measured in the slave appears longer than the (t4 - t1)
+	 * measured in the master.  Ignore such values, by skipping
+	 * the filter and keeping the current average instead.
+	 */
+	if (owd->nanoseconds > 0) {
 		/* avoid overflowing filter */
 		s = OPTS(ppi)->s;
 		while (abs(owd_fltr->y) >> (31 - s))
@@ -136,12 +144,11 @@ void pp_servo_got_resp(struct pp_instance *ppi)
 		owd_fltr->y = (owd_fltr->y * (owd_fltr->s_exp - 1)
 			       + owd->nanoseconds)
 			/ owd_fltr->s_exp;
-
-		owd->nanoseconds = owd_fltr->y;
-
-		pp_diag(ppi, servo, 1, "After avg(%i), one-way delay: %i\n",
-			(int)owd_fltr->s_exp, owd->nanoseconds);
 	}
+	owd->nanoseconds = owd_fltr->y;
+
+	pp_diag(ppi, servo, 1, "After avg(%i), one-way delay: %i\n",
+		(int)owd_fltr->s_exp, owd->nanoseconds);

 	/* update 'offsetFromMaster', (End to End mode) */
 	sub_TimeInternal(ofm, m_to_s_dly, owd);