2 * collectd - src/utils_latency.c
3 * Copyright (C) 2013 Florian Forster
5 * Permission is hereby granted, free of charge, to any person obtaining a
6 * copy of this software and associated documentation files (the "Software"),
7 * to deal in the Software without restriction, including without limitation
8 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
9 * and/or sell copies of the Software, and to permit persons to whom the
10 * Software is furnished to do so, subject to the following conditions:
12 * The above copyright notice and this permission notice shall be included in
13 * all copies or substantial portions of the Software.
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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21 * DEALINGS IN THE SOFTWARE.
24 * Florian Forster <ff at octo.it>
29 #include "utils_latency.h"
34 #ifndef HISTOGRAM_NUM_BINS
35 # define HISTOGRAM_NUM_BINS 1000
38 static const int HISTOGRAM_DEFAULT_BIN_WIDTH = 1;
40 struct latency_counter_s
51 int histogram[HISTOGRAM_NUM_BINS];
55 * Histogram represents the distribution of data, it has a list of "bins".
56 * Each bin represents an interval and has a count (frequency) of
57 * number of values fall within its interval.
59 * Histogram's range is determined by the number of bins and the bin width,
60 * There are 1000 bins and all bins have the same width of default 1 millisecond.
61 * When a value above this range is added, Histogram's range is increased by
62 * increasing the bin width (note that number of bins remains always at 1000).
63 * This operation of increasing bin width is little expensive as each bin need
64 * to be visited to update it's count. To reduce frequent change of bin width,
65 * new bin width will be the next nearest power of 2. Example: 2, 4, 8, 16, 32,
66 * 64, 128, 256, 512, 1024, 2048, 5086, ...
68 * So, if the required bin width is 300, then new bin width will be 512 as it is
69 * the next nearest power of 2.
71 void change_bin_width (latency_counter_t *lc, size_t val) /* {{{ */
73 /* This function is called because the new value is above histogram's range.
74 * First find the required bin width:
75 * requiredBinWidth = (value + 1) / numBins
76 * then get the next nearest power of 2
77 * newBinWidth = 2^(ceil(log2(requiredBinWidth)))
79 double required_bin_width = (double)(val + 1) / HISTOGRAM_NUM_BINS;
80 double required_bin_width_logbase2 = log(required_bin_width) / log(2.0);
81 int new_bin_width = (int)(pow(2.0, ceil( required_bin_width_logbase2)));
82 int old_bin_width = lc->bin_width;
84 lc->bin_width = new_bin_width;
87 * bin width has been increased, now iterate through all bins and move the
88 * old bin's count to new bin.
90 if (lc->num > 0) // if the histogram has data then iterate else skip
92 double width_change_ratio = ((double) old_bin_width) / ((double) new_bin_width);
95 for (i = 0; i < HISTOGRAM_NUM_BINS; i++)
97 size_t new_bin = (size_t) (((double) i) * width_change_ratio);
100 assert (new_bin < i);
102 if (lc->histogram[i] != 0) {
103 DEBUG ("utils_latency: moving %d from %zu to %zu.", lc->histogram[i], i, new_bin);
105 lc->histogram[new_bin] += lc->histogram[i];
106 lc->histogram[i] = 0;
110 DEBUG("utils_latency: change_bin_width: val-[%zu], oldBinWidth-[%d], "
111 "newBinWidth-[%d], required_bin_width-[%f], "
112 "required_bin_width_logbase2-[%f]",
113 val, old_bin_width, new_bin_width, required_bin_width,
114 required_bin_width_logbase2);
115 } /* }}} void change_bin_width */
117 latency_counter_t *latency_counter_create () /* {{{ */
119 latency_counter_t *lc;
121 lc = malloc (sizeof (*lc));
124 memset (lc, 0, sizeof (*lc));
126 latency_counter_reset (lc);
127 lc->bin_width = HISTOGRAM_DEFAULT_BIN_WIDTH;
129 } /* }}} latency_counter_t *latency_counter_create */
131 void latency_counter_destroy (latency_counter_t *lc) /* {{{ */
134 } /* }}} void latency_counter_destroy */
136 void latency_counter_add (latency_counter_t *lc, cdtime_t latency) /* {{{ */
140 if ((lc == NULL) || (latency == 0))
146 if ((lc->min == 0) && (lc->max == 0))
147 lc->min = lc->max = latency;
148 if (lc->min > latency)
150 if (lc->max < latency)
153 /* A latency of _exactly_ 1.0 ms should be stored in the buffer 0, so
154 * subtract one from the cdtime_t value so that exactly 1.0 ms get sorted
156 latency_ms = (size_t) CDTIME_T_TO_MS (latency - 1);
158 int bin = (int)(latency_ms / lc->bin_width);
159 if (bin >= HISTOGRAM_NUM_BINS)
161 change_bin_width(lc, latency_ms);
162 bin = (int)(latency_ms / lc->bin_width);
163 if (bin >= HISTOGRAM_NUM_BINS)
165 ERROR("utils_latency: latency_counter_add: Invalid bin %d", bin);
169 lc->histogram[bin]++;
170 } /* }}} void latency_counter_add */
172 void latency_counter_reset (latency_counter_t *lc) /* {{{ */
177 int bin_width = lc->bin_width;
178 memset (lc, 0, sizeof (*lc));
180 /* preserve bin width */
181 lc->bin_width = bin_width;
182 lc->start_time = cdtime ();
183 } /* }}} void latency_counter_reset */
185 cdtime_t latency_counter_get_min (latency_counter_t *lc) /* {{{ */
190 } /* }}} cdtime_t latency_counter_get_min */
192 cdtime_t latency_counter_get_max (latency_counter_t *lc) /* {{{ */
197 } /* }}} cdtime_t latency_counter_get_max */
199 cdtime_t latency_counter_get_sum (latency_counter_t *lc) /* {{{ */
204 } /* }}} cdtime_t latency_counter_get_sum */
206 size_t latency_counter_get_num (latency_counter_t *lc) /* {{{ */
211 } /* }}} size_t latency_counter_get_num */
213 cdtime_t latency_counter_get_average (latency_counter_t *lc) /* {{{ */
217 if ((lc == NULL) || (lc->num == 0))
220 average = CDTIME_T_TO_DOUBLE (lc->sum) / ((double) lc->num);
221 return (DOUBLE_TO_CDTIME_T (average));
222 } /* }}} cdtime_t latency_counter_get_average */
224 cdtime_t latency_counter_get_percentile (latency_counter_t *lc,
227 double percent_upper;
228 double percent_lower;
231 double ms_interpolated;
235 if ((lc == NULL) || (lc->num == 0) || !((percent > 0.0) && (percent < 100.0)))
238 /* Find index i so that at least "percent" events are within i+1 ms. */
242 for (i = 0; i < HISTOGRAM_NUM_BINS; i++)
244 percent_lower = percent_upper;
245 sum += lc->histogram[i];
249 percent_upper = 100.0 * ((double) sum) / ((double) lc->num);
251 if (percent_upper >= percent)
255 if (i >= HISTOGRAM_NUM_BINS)
258 assert (percent_upper >= percent);
259 assert (percent_lower < percent);
261 ms_upper = (double) ( (i + 1) * lc->bin_width );
262 ms_lower = (double) ( i * lc->bin_width );
264 return (MS_TO_CDTIME_T (ms_upper));
266 ms_interpolated = (((percent_upper - percent) * ms_lower)
267 + ((percent - percent_lower) * ms_upper))
268 / (percent_upper - percent_lower);
270 return (MS_TO_CDTIME_T (ms_interpolated));
271 } /* }}} cdtime_t latency_counter_get_percentile */
273 /* vim: set sw=2 sts=2 et fdm=marker : */