src/utils_latency.[ch]: Improve accuracy, update unit test.

[collectd.git] / src / utils_latency.c

diff --git a/src/utils_latency.c b/src/utils_latency.c
index c67752a..1a82eab 100644 (file)
--- a/src/utils_latency.c
+++ b/src/utils_latency.c
@@ -37,10 +37,6 @@
 # define LLONG_MAX 9223372036854775807LL
 #endif
 
-#ifndef HISTOGRAM_NUM_BINS
-# define HISTOGRAM_NUM_BINS 1000
-#endif
-
 #ifndef HISTOGRAM_DEFAULT_BIN_WIDTH
 /* 1048576 = 2^20 ^= 1/1024 s */
 # define HISTOGRAM_DEFAULT_BIN_WIDTH 1048576
@@ -152,7 +148,7 @@ void latency_counter_add (latency_counter_t *lc, cdtime_t latency) /* {{{ */
   if (lc->max < latency)
     lc->max = latency;
 
-  /* A latency of _exactly_ 1.0 ms should be stored in the buffer 0, so
+  /* A latency of _exactly_ 1.0 ms is stored in the buffer 0, so
    * subtract one from the cdtime_t value so that exactly 1.0 ms get sorted
    * accordingly. */
   bin = (latency - 1) / lc->bin_width;
@@ -294,4 +290,76 @@ cdtime_t latency_counter_get_percentile (latency_counter_t *lc, /* {{{ */
   return (latency_interpolated);
 } /* }}} cdtime_t latency_counter_get_percentile */
 
+cdtime_t latency_counter_get_start_time (const latency_counter_t *lc) /* {{{ */
+{
+  if (lc == NULL)
+    return (0);
+
+  return lc->start_time;
+} /* }}} cdtime_t latency_counter_get_start_time */
+
+
+double latency_counter_get_rate (const latency_counter_t *lc, /* {{{ */
+        cdtime_t lower, cdtime_t upper, const cdtime_t now)
+{
+  cdtime_t lower_bin;
+  cdtime_t upper_bin;
+  double sum = 0;
+
+  if ((lc == NULL) || (lc->num == 0))
+    return (0);
+
+  if (upper && (upper < lower))
+    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 lower==bin_width needs to result in lower_bin=0, hence the -1. */
+  if (lower)
+    lower_bin = (lower - 1) / lc->bin_width;
+  else
+    lower_bin = 0;
+
+  if (upper)
+    upper_bin = (upper - 1) / lc->bin_width;
+  else
+    upper_bin = HISTOGRAM_NUM_BINS - 1;
+
+  if (lower_bin >= HISTOGRAM_NUM_BINS)
+    lower_bin = HISTOGRAM_NUM_BINS - 1;
+
+  if (upper_bin >= HISTOGRAM_NUM_BINS) {
+    upper_bin = HISTOGRAM_NUM_BINS - 1;
+    upper = 0;
+  }
+
+  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 - 1) / ((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 */
+
 /* vim: set sw=2 sts=2 et fdm=marker : */