/**
* collectd - src/utils_latency.c
- * Copyright (C) 2013 Florian Forster
+ * Copyright (C) 2013 Florian Forster
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
**/
#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
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 */
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;
/* 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) /* {{{ */
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 */
{
double average;
- if (lc == NULL)
+ if ((lc == NULL) || (lc->num == 0))
return (0);
average = CDTIME_T_TO_DOUBLE (lc->sum) / ((double) lc->num);
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;
- if ((lc == NULL) || !((percent > 0.0) && (percent < 100.0)))
+ if ((lc == NULL) || (lc->num == 0) || !((percent > 0.0) && (percent < 100.0)))
return (0);
/* Find index i so that at least "percent" events are within i+1 ms. */
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];
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 : */
projects / collectd.git / blobdiff