X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=src%2Futils_latency.c;h=ca7d5fab3d582672554f344fb9ed60791fdbb1f1;hb=f14feb1eddfe5760a64640b98ab7bbc5c493f614;hp=91ddd5fd92485c0a02d6642b56ce346334f40b50;hpb=0febfbd11d87acd8a0f10bbcf5d4a58bb68b8dc0;p=collectd.git

diff --git a/src/utils_latency.c b/src/utils_latency.c
index 91ddd5fd..ca7d5fab 100644
--- a/src/utils_latency.c
+++ b/src/utils_latency.c
@@ -25,11 +25,24 @@
  **/
 
 #include "collectd.h"
+#include "plugin.h"
 #include "utils_latency.h"
 #include "common.h"
 
-#ifndef LATENCY_HISTOGRAM_SIZE
-# define LATENCY_HISTOGRAM_SIZE 1000
+#include <math.h>
+#include <limits.h>
+
+#ifndef LLONG_MAX
+# 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
 #endif
 
 struct latency_counter_s
@@ -42,18 +55,79 @@ struct latency_counter_s
   cdtime_t min;
   cdtime_t max;
 
-  int histogram[LATENCY_HISTOGRAM_SIZE];
+  cdtime_t bin_width;
+  int histogram[HISTOGRAM_NUM_BINS];
 };
 
-latency_counter_t *latency_counter_create () /* {{{ */
+/*
+* Histogram represents the distribution of data, it has a list of "bins".
+* Each bin represents an interval and has a count (frequency) of
+* number of values fall within its interval.
+*
+* Histogram's range is determined by the number of bins and the bin width,
+* There are 1000 bins and all bins have the same width of default 1 millisecond.
+* When a value above this range is added, Histogram's range is increased by
+* increasing the bin width (note that number of bins remains always at 1000).
+* This operation of increasing bin width is little expensive as each bin need
+* to be visited to update it's count. To reduce frequent change of bin width,
+* new bin width will be the next nearest power of 2. Example: 2, 4, 8, 16, 32,
+* 64, 128, 256, 512, 1024, 2048, 5086, ...
+*
+* So, if the required bin width is 300, then new bin width will be 512 as it is
+* the next nearest power of 2.
+*/
+static void change_bin_width (latency_counter_t *lc, cdtime_t latency) /* {{{ */
+{
+  /* This function is called because the new value is above histogram's range.
+   * First find the required bin width:
+   *           requiredBinWidth = (value + 1) / numBins
+   * then get the next nearest power of 2
+   *           newBinWidth = 2^(ceil(log2(requiredBinWidth)))
+   */
+  double required_bin_width = ((double) (latency + 1)) / ((double) HISTOGRAM_NUM_BINS);
+  double required_bin_width_logbase2 = log (required_bin_width) / log (2.0);
+  cdtime_t new_bin_width = (cdtime_t) (pow (2.0, ceil (required_bin_width_logbase2)) + .5);
+  cdtime_t old_bin_width = lc->bin_width;
+
+  lc->bin_width = new_bin_width;
+
+  /* bin_width has been increased, now iterate through all bins and move the
+   * old bin's count to new bin. */
+  if (lc->num > 0) // if the histogram has data then iterate else skip
+  {
+      double width_change_ratio = ((double) old_bin_width) / ((double) new_bin_width);
+      size_t i;
+
+      for (i = 0; i < HISTOGRAM_NUM_BINS; i++)
+      {
+         size_t new_bin = (size_t) (((double) i) * width_change_ratio);
+         if (i == new_bin)
+             continue;
+         assert (new_bin < i);
+
+         lc->histogram[new_bin] += lc->histogram[i];
+         lc->histogram[i] = 0;
+      }
+  }
+
+  DEBUG("utils_latency: change_bin_width: latency = %.3f; "
+      "old_bin_width = %.3f; new_bin_width = %.3f;",
+      CDTIME_T_TO_DOUBLE (latency),
+      CDTIME_T_TO_DOUBLE (old_bin_width),
+      CDTIME_T_TO_DOUBLE (new_bin_width));
+} /* }}} void change_bin_width */
+
+latency_counter_t *latency_counter_create (void) /* {{{ */
 {
   latency_counter_t *lc;
 
   lc = malloc (sizeof (*lc));
   if (lc == NULL)
     return (NULL);
+  memset (lc, 0, sizeof (*lc));
 
   latency_counter_reset (lc);
+  lc->bin_width = HISTOGRAM_DEFAULT_BIN_WIDTH;
   return (lc);
 } /* }}} latency_counter_t *latency_counter_create */
 
@@ -64,9 +138,9 @@ void latency_counter_destroy (latency_counter_t *lc) /* {{{ */
 
 void latency_counter_add (latency_counter_t *lc, cdtime_t latency) /* {{{ */
 {
-  size_t latency_ms;
+  cdtime_t bin;
 
-  if ((lc == NULL) || (latency == 0))
+  if ((lc == NULL) || (latency == 0) || (latency > ((cdtime_t) LLONG_MAX)))
     return;
 
   lc->sum += latency;
@@ -82,9 +156,18 @@ void latency_counter_add (latency_counter_t *lc, cdtime_t latency) /* {{{ */
   /* A latency of _exactly_ 1.0 ms should be stored in the buffer 0, so
    * subtract one from the cdtime_t value so that exactly 1.0 ms get sorted
    * accordingly. */
-  latency_ms = (size_t) CDTIME_T_TO_MS (latency - 1);
-  if (latency_ms < STATIC_ARRAY_SIZE (lc->histogram))
-    lc->histogram[latency_ms]++;
+  bin = (latency - 1) / lc->bin_width;
+  if (bin >= HISTOGRAM_NUM_BINS)
+  {
+      change_bin_width (lc, latency);
+      bin = (latency - 1) / lc->bin_width;
+      if (bin >= HISTOGRAM_NUM_BINS)
+      {
+          ERROR ("utils_latency: latency_counter_add: Invalid bin: %"PRIu64, bin);
+          return;
+      }
+  }
+  lc->histogram[bin]++;
 } /* }}} void latency_counter_add */
 
 void latency_counter_reset (latency_counter_t *lc) /* {{{ */
@@ -92,7 +175,11 @@ void latency_counter_reset (latency_counter_t *lc) /* {{{ */
   if (lc == NULL)
     return;
 
+  cdtime_t bin_width = lc->bin_width;
   memset (lc, 0, sizeof (*lc));
+
+  /* preserve bin width */
+  lc->bin_width = bin_width;
   lc->start_time = cdtime ();
 } /* }}} void latency_counter_reset */
 
@@ -135,14 +222,14 @@ cdtime_t latency_counter_get_average (latency_counter_t *lc) /* {{{ */
   return (DOUBLE_TO_CDTIME_T (average));
 } /* }}} cdtime_t latency_counter_get_average */
 
-cdtime_t latency_counter_get_percentile (latency_counter_t *lc,
+cdtime_t latency_counter_get_percentile (latency_counter_t *lc, /* {{{ */
     double percent)
 {
   double percent_upper;
   double percent_lower;
-  double ms_upper;
-  double ms_lower;
-  double ms_interpolated;
+  double p;
+  cdtime_t latency_lower;
+  cdtime_t latency_interpolated;
   int sum;
   size_t i;
 
@@ -153,7 +240,7 @@ cdtime_t latency_counter_get_percentile (latency_counter_t *lc,
   percent_upper = 0.0;
   percent_lower = 0.0;
   sum = 0;
-  for (i = 0; i < LATENCY_HISTOGRAM_SIZE; i++)
+  for (i = 0; i < HISTOGRAM_NUM_BINS; i++)
   {
     percent_lower = percent_upper;
     sum += lc->histogram[i];
@@ -166,22 +253,24 @@ cdtime_t latency_counter_get_percentile (latency_counter_t *lc,
       break;
   }
 
-  if (i >= LATENCY_HISTOGRAM_SIZE)
+  if (i >= HISTOGRAM_NUM_BINS)
     return (0);
 
   assert (percent_upper >= percent);
   assert (percent_lower < percent);
 
-  ms_upper = (double) (i + 1);
-  ms_lower = (double) i;
   if (i == 0)
-    return (MS_TO_CDTIME_T (ms_upper));
+    return (lc->bin_width);
+
+  latency_lower = ((cdtime_t) i) * lc->bin_width;
+  p = (percent - percent_lower) / (percent_upper - percent_lower);
 
-  ms_interpolated = (((percent_upper - percent) * ms_lower)
-      + ((percent - percent_lower) * ms_upper))
-    / (percent_upper - percent_lower);
+  latency_interpolated = latency_lower
+    + DOUBLE_TO_CDTIME_T (p * CDTIME_T_TO_DOUBLE (lc->bin_width));
 
-  return (MS_TO_CDTIME_T (ms_interpolated));
+  DEBUG ("latency_counter_get_percentile: latency_interpolated = %.3f",
+      CDTIME_T_TO_DOUBLE (latency_interpolated));
+  return (latency_interpolated);
 } /* }}} cdtime_t latency_counter_get_percentile */
 
 /* vim: set sw=2 sts=2 et fdm=marker : */