1 /**
2 * collectd - src/utils_latency.c
3 * Copyright (C) 2013 Florian Forster
4 *
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:
11 *
12 * The above copyright notice and this permission notice shall be included in
13 * all copies or substantial portions of the Software.
14 *
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
18 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
21 * DEALINGS IN THE SOFTWARE.
22 *
23 * Authors:
24 * Florian Forster <ff at octo.it>
25 **/
27 #include "collectd.h"
28 #include "plugin.h"
29 #include "utils_latency.h"
30 #include "common.h"
32 #include <math.h>
33 #include <limits.h>
35 #ifndef LLONG_MAX
36 # define LLONG_MAX 9223372036854775807LL
37 #endif
39 #ifndef HISTOGRAM_NUM_BINS
40 # define HISTOGRAM_NUM_BINS 1000
41 #endif
43 #ifndef HISTOGRAM_DEFAULT_BIN_WIDTH
44 /* 1048576 = 2^20 ^= 1/1024 s */
45 # define HISTOGRAM_DEFAULT_BIN_WIDTH 1048576
46 #endif
48 struct latency_counter_s
49 {
50 cdtime_t start_time;
52 cdtime_t sum;
53 size_t num;
55 cdtime_t min;
56 cdtime_t max;
58 cdtime_t bin_width;
59 int histogram[HISTOGRAM_NUM_BINS];
60 };
62 /*
63 * Histogram represents the distribution of data, it has a list of "bins".
64 * Each bin represents an interval and has a count (frequency) of
65 * number of values fall within its interval.
66 *
67 * Histogram's range is determined by the number of bins and the bin width,
68 * There are 1000 bins and all bins have the same width of default 1 millisecond.
69 * When a value above this range is added, Histogram's range is increased by
70 * increasing the bin width (note that number of bins remains always at 1000).
71 * This operation of increasing bin width is little expensive as each bin need
72 * to be visited to update it's count. To reduce frequent change of bin width,
73 * new bin width will be the next nearest power of 2. Example: 2, 4, 8, 16, 32,
74 * 64, 128, 256, 512, 1024, 2048, 5086, ...
75 *
76 * So, if the required bin width is 300, then new bin width will be 512 as it is
77 * the next nearest power of 2.
78 */
79 static void change_bin_width (latency_counter_t *lc, cdtime_t latency) /* {{{ */
80 {
81 /* This function is called because the new value is above histogram's range.
82 * First find the required bin width:
83 * requiredBinWidth = (value + 1) / numBins
84 * then get the next nearest power of 2
85 * newBinWidth = 2^(ceil(log2(requiredBinWidth)))
86 */
87 double required_bin_width = ((double) (latency + 1)) / ((double) HISTOGRAM_NUM_BINS);
88 double required_bin_width_logbase2 = log (required_bin_width) / log (2.0);
89 cdtime_t new_bin_width = (cdtime_t) (pow (2.0, ceil (required_bin_width_logbase2)) + .5);
90 cdtime_t old_bin_width = lc->bin_width;
92 lc->bin_width = new_bin_width;
94 /* bin_width has been increased, now iterate through all bins and move the
95 * old bin's count to new bin. */
96 if (lc->num > 0) // if the histogram has data then iterate else skip
97 {
98 double width_change_ratio = ((double) old_bin_width) / ((double) new_bin_width);
99 size_t i;
101 for (i = 0; i < HISTOGRAM_NUM_BINS; i++)
102 {
103 size_t new_bin = (size_t) (((double) i) * width_change_ratio);
104 if (i == new_bin)
105 continue;
106 assert (new_bin < i);
108 lc->histogram[new_bin] += lc->histogram[i];
109 lc->histogram[i] = 0;
110 }
111 }
113 DEBUG("utils_latency: change_bin_width: latency = %.3f; "
114 "old_bin_width = %.3f; new_bin_width = %.3f;",
115 CDTIME_T_TO_DOUBLE (latency),
116 CDTIME_T_TO_DOUBLE (old_bin_width),
117 CDTIME_T_TO_DOUBLE (new_bin_width));
118 } /* }}} void change_bin_width */
120 latency_counter_t *latency_counter_create (void) /* {{{ */
121 {
122 latency_counter_t *lc;
124 lc = calloc (1, sizeof (*lc));
125 if (lc == NULL)
126 return (NULL);
128 latency_counter_reset (lc);
129 lc->bin_width = HISTOGRAM_DEFAULT_BIN_WIDTH;
130 return (lc);
131 } /* }}} latency_counter_t *latency_counter_create */
133 void latency_counter_destroy (latency_counter_t *lc) /* {{{ */
134 {
135 sfree (lc);
136 } /* }}} void latency_counter_destroy */
138 void latency_counter_add (latency_counter_t *lc, cdtime_t latency) /* {{{ */
139 {
140 cdtime_t bin;
142 if ((lc == NULL) || (latency == 0) || (latency > ((cdtime_t) LLONG_MAX)))
143 return;
145 lc->sum += latency;
146 lc->num++;
148 if ((lc->min == 0) && (lc->max == 0))
149 lc->min = lc->max = latency;
150 if (lc->min > latency)
151 lc->min = latency;
152 if (lc->max < latency)
153 lc->max = latency;
155 /* A latency of _exactly_ 1.0 ms should be stored in the buffer 0, so
156 * subtract one from the cdtime_t value so that exactly 1.0 ms get sorted
157 * accordingly. */
158 bin = (latency - 1) / lc->bin_width;
159 if (bin >= HISTOGRAM_NUM_BINS)
160 {
161 change_bin_width (lc, latency);
162 bin = (latency - 1) / lc->bin_width;
163 if (bin >= HISTOGRAM_NUM_BINS)
164 {
165 ERROR ("utils_latency: latency_counter_add: Invalid bin: %"PRIu64, bin);
166 return;
167 }
168 }
169 lc->histogram[bin]++;
170 } /* }}} void latency_counter_add */
172 void latency_counter_reset (latency_counter_t *lc) /* {{{ */
173 {
174 if (lc == NULL)
175 return;
177 cdtime_t 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) /* {{{ */
186 {
187 if (lc == NULL)
188 return (0);
189 return (lc->min);
190 } /* }}} cdtime_t latency_counter_get_min */
192 cdtime_t latency_counter_get_max (latency_counter_t *lc) /* {{{ */
193 {
194 if (lc == NULL)
195 return (0);
196 return (lc->max);
197 } /* }}} cdtime_t latency_counter_get_max */
199 cdtime_t latency_counter_get_sum (latency_counter_t *lc) /* {{{ */
200 {
201 if (lc == NULL)
202 return (0);
203 return (lc->sum);
204 } /* }}} cdtime_t latency_counter_get_sum */
206 size_t latency_counter_get_num (latency_counter_t *lc) /* {{{ */
207 {
208 if (lc == NULL)
209 return (0);
210 return (lc->num);
211 } /* }}} size_t latency_counter_get_num */
213 cdtime_t latency_counter_get_average (latency_counter_t *lc) /* {{{ */
214 {
215 double average;
217 if ((lc == NULL) || (lc->num == 0))
218 return (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, /* {{{ */
225 double percent)
226 {
227 double percent_upper;
228 double percent_lower;
229 double p;
230 cdtime_t latency_lower;
231 cdtime_t latency_interpolated;
232 int sum;
233 size_t i;
235 if ((lc == NULL) || (lc->num == 0) || !((percent > 0.0) && (percent < 100.0)))
236 return (0);
238 /* Find index i so that at least "percent" events are within i+1 ms. */
239 percent_upper = 0.0;
240 percent_lower = 0.0;
241 sum = 0;
242 for (i = 0; i < HISTOGRAM_NUM_BINS; i++)
243 {
244 percent_lower = percent_upper;
245 sum += lc->histogram[i];
246 if (sum == 0)
247 percent_upper = 0.0;
248 else
249 percent_upper = 100.0 * ((double) sum) / ((double) lc->num);
251 if (percent_upper >= percent)
252 break;
253 }
255 if (i >= HISTOGRAM_NUM_BINS)
256 return (0);
258 assert (percent_upper >= percent);
259 assert (percent_lower < percent);
261 if (i == 0)
262 return (lc->bin_width);
264 latency_lower = ((cdtime_t) i) * lc->bin_width;
265 p = (percent - percent_lower) / (percent_upper - percent_lower);
267 latency_interpolated = latency_lower
268 + DOUBLE_TO_CDTIME_T (p * CDTIME_T_TO_DOUBLE (lc->bin_width));
270 DEBUG ("latency_counter_get_percentile: latency_interpolated = %.3f",
271 CDTIME_T_TO_DOUBLE (latency_interpolated));
272 return (latency_interpolated);
273 } /* }}} cdtime_t latency_counter_get_percentile */
275 /* vim: set sw=2 sts=2 et fdm=marker : */