On Wed, 20 Jan 2016, Peter Zijlstra wrote:

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

quoted

+static inline u32 stats_mean(struct stats *s)
+{
+	/*
+	 * gcc is smart enough to convert to a bits shift when the
+	 * divisor is constant and multiple of 2^x.
+	 *
+	 * The number of values could have not reached STATS_NR_VALUES
+	 * yet, but we can consider it acceptable as the situation is
+	 * only at the beginning of the burst of irqs.
+	 */
+	return s->sum / STATS_NR_VALUES;
+}

Note that ->sum is u64, so you're very prone to truncation.

It won't.  It is the sum of u32 values, so the mean of those values 
can't exceed 32 bits.


Nicolas