On Wed, Jan 20, 2016 at 05:00:33PM +0100, Daniel Lezcano wrote:

+		variance = stats_variance(&w->stats, mean);
+		/*
+		 * We want to check the last interval is:
+		 *
+		 *  mean - stddev < interval < mean + stddev
+		 *
+		 * That simplifies to:
+		 *
+		 * -stddev < interval - mean < stddev
+		 *
+		 * abs(interval - mean) < stddev
+		 *
+		 * The standard deviation is the sqrt of the variance:
+		 *
+		 * abs(interval - mean) < sqrt(variance)
+		 *
+		 * and we want to prevent to do an sqrt, so we square
+		 * the equation:
+		 *
+		 * (interval - mean)^2 < variance
+		 *
+		 * So if the latest value of the stats complies with
+		 * this condition, then the wakeup source is
+		 * considered predictable and can be used to predict
+		 * the next event.
+		 */
+		interval = w->stats.values[w->stats.w_ptr];
+		if ((u64)((interval - mean) * (interval - mean)) > variance)
+			continue;
+

Cute :-)

You could consider putting a simple 3 point median filter in front of
stat_add() to get rid of the worst input noise.

(I know, improving all this was a point for later)