+double latency_counter_get_rate(const latency_counter_t *lc, /* {{{ */
+ cdtime_t lower, cdtime_t upper,
+ const cdtime_t now) {
+ if ((lc == NULL) || (lc->num == 0))
+ return (NAN);
+
+ if (upper && (upper < lower))
+ return (NAN);
+ if (lower == upper)
+ return (0);
+
+ /* Buckets have an exclusive lower bound and an inclusive upper bound. That
+ * means that the first bucket, index 0, represents (0-bin_width]. That means
+ * that latency==bin_width needs to result in bin=0, that's why we need to
+ * subtract one before dividing by bin_width. */
+ cdtime_t lower_bin = 0;
+ if (lower)
+ /* lower is *exclusive* => determine bucket for lower+1 */
+ lower_bin = ((lower + 1) - 1) / lc->bin_width;
+
+ /* lower is greater than the longest latency observed => rate is zero. */
+ if (lower_bin >= HISTOGRAM_NUM_BINS)
+ return (0);
+
+ cdtime_t upper_bin = HISTOGRAM_NUM_BINS - 1;
+ if (upper)
+ upper_bin = (upper - 1) / lc->bin_width;
+
+ if (upper_bin >= HISTOGRAM_NUM_BINS) {
+ upper_bin = HISTOGRAM_NUM_BINS - 1;
+ upper = 0;
+ }
+
+ double sum = 0;
+ for (size_t i = lower_bin; i <= upper_bin; i++)
+ sum += lc->histogram[i];
+
+ if (lower) {
+ /* Approximate ratio of requests in lower_bin, that fall between
+ * lower_bin_boundary and lower. This ratio is then subtracted from sum to
+ * increase accuracy. */
+ cdtime_t lower_bin_boundary = lower_bin * lc->bin_width;
+ assert(lower >= lower_bin_boundary);
+ double lower_ratio =
+ (double)(lower - lower_bin_boundary) / ((double)lc->bin_width);
+ sum -= lower_ratio * lc->histogram[lower_bin];
+ }
+
+ if (upper) {
+ /* As above: approximate ratio of requests in upper_bin, that fall between
+ * upper and upper_bin_boundary. */
+ cdtime_t upper_bin_boundary = (upper_bin + 1) * lc->bin_width;
+ assert(upper <= upper_bin_boundary);
+ double ratio = (double)(upper_bin_boundary - upper) / (double)lc->bin_width;
+ sum -= ratio * lc->histogram[upper_bin];
+ }
+
+ return sum / (CDTIME_T_TO_DOUBLE(now - lc->start_time));
+} /* }}} double latency_counter_get_rate */
+