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1/*
2 This file is part of GNUnet.
3 Copyright (C) 2010, 2013 GNUnet e.V.
4
5 GNUnet is free software: you can redistribute it and/or modify it
6 under the terms of the GNU Affero General Public License as published
7 by the Free Software Foundation, either version 3 of the License,
8 or (at your option) any later version.
9
10 GNUnet is distributed in the hope that it will be useful, but
11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Affero General Public License for more details.
14
15 You should have received a copy of the GNU Affero General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
17
18 SPDX-License-Identifier: AGPL3.0-or-later
19 */
20
21/**
22 * @file util/load.c
23 * @brief functions related to load calculations
24 * @author Christian Grothoff
25 */
26#include "platform.h"
27#include "gnunet_util_lib.h"
28
29
30#define LOG(kind, ...) GNUNET_log_from (kind, "util-load", __VA_ARGS__)
31
32/**
33 * Values we track for load calculations.
34 */
35struct GNUNET_LOAD_Value
36{
37 /**
38 * How fast should the load decline if no values are added?
39 */
40 struct GNUNET_TIME_Relative autodecline;
41
42 /**
43 * Last time this load value was updated by an event.
44 */
45 struct GNUNET_TIME_Absolute last_update;
46
47 /**
48 * Sum of all datastore delays ever observed (in ms). Note that
49 * delays above 64k ms are excluded (to avoid overflow within
50 * first 4 billion requests).
51 */
52 uint64_t cummulative_delay;
53
54 /**
55 * Sum of squares of all datastore delays ever observed (in ms). Note that
56 * delays above 64k ms are excluded (to avoid overflow within
57 * first 4 billion requests).
58 */
59 uint64_t cummulative_squared_delay;
60
61 /**
62 * Total number of requests included in the cumulative datastore delay values.
63 */
64 uint64_t cummulative_request_count;
65
66 /**
67 * Current running average datastore delay. Its relation to the
68 * average datastore delay and it std. dev. (as calculated from the
69 * cumulative values) tells us our current load.
70 */
71 double runavg_delay;
72
73 /**
74 * How high is the load? 0 for below average, otherwise
75 * the number of std. devs we are above average, or 100 if the
76 * load is so high that we currently cannot calculate it.
77 */
78 double load;
79};
80
81
82static void
83internal_update (struct GNUNET_LOAD_Value *load)
84{
85 struct GNUNET_TIME_Relative delta;
86 unsigned int n;
87
88 if (load->autodecline.rel_value_us ==
89 GNUNET_TIME_UNIT_FOREVER_REL.rel_value_us)
90 return;
91 delta = GNUNET_TIME_absolute_get_duration (load->last_update);
92 if (delta.rel_value_us < load->autodecline.rel_value_us)
93 return;
94 if (0 == load->autodecline.rel_value_us)
95 {
96 load->runavg_delay = 0.0;
97 load->load = 0;
98 return;
99 }
100 n = delta.rel_value_us / load->autodecline.rel_value_us;
101 if (n > 16)
102 {
103 load->runavg_delay = 0.0;
104 load->load = 0;
105 return;
106 }
107 while (n > 0)
108 {
109 n--;
110 load->runavg_delay = (load->runavg_delay * 7.0) / 8.0;
111 }
112}
113
114
115/**
116 * Create a new load value.
117 *
118 * @param autodecline speed at which this value should automatically
119 * decline in the absence of external events; at the given
120 * frequency, 0-load values will be added to the load
121 * @return the new load value
122 */
123struct GNUNET_LOAD_Value *
124GNUNET_LOAD_value_init (struct GNUNET_TIME_Relative autodecline)
125{
126 struct GNUNET_LOAD_Value *ret;
127
128 ret = GNUNET_new (struct GNUNET_LOAD_Value);
129 ret->autodecline = autodecline;
130 ret->last_update = GNUNET_TIME_absolute_get ();
131 return ret;
132}
133
134
135/**
136 * Change the value by which the load automatically declines.
137 *
138 * @param load load to update
139 * @param autodecline frequency of load decline
140 */
141void
142GNUNET_LOAD_value_set_decline (struct GNUNET_LOAD_Value *load,
143 struct GNUNET_TIME_Relative autodecline)
144{
145 internal_update (load);
146 load->autodecline = autodecline;
147}
148
149
150/**
151 * Recalculate our load value.
152 *
153 * @param load load to update
154 */
155static void
156calculate_load (struct GNUNET_LOAD_Value *load)
157{
158 double stddev;
159 double avgdel;
160 double sum_val_i;
161 double n;
162 double nm1;
163
164 if (load->cummulative_request_count <= 1)
165 return;
166 /* calculate std dev of latency; we have for n values of "i" that:
167 *
168 * avg = (sum val_i) / n
169 * stddev = (sum (val_i - avg)^2) / (n-1)
170 * = (sum (val_i^2 - 2 avg val_i + avg^2) / (n-1)
171 * = (sum (val_i^2) - 2 avg sum (val_i) + n * avg^2) / (n-1)
172 */sum_val_i = (double) load->cummulative_delay;
173 n = ((double) load->cummulative_request_count);
174 nm1 = n - 1.0;
175 avgdel = sum_val_i / n;
176 stddev =
177 (((double) load->cummulative_squared_delay) - 2.0 * avgdel * sum_val_i
178 + n * avgdel * avgdel) / nm1;
179 if (stddev <= 0)
180 stddev = 0.01; /* must have been rounding error or zero; prevent division by zero */
181 /* now calculate load based on how far out we are from
182 * std dev; or if we are below average, simply assume load zero */
183 if (load->runavg_delay < avgdel)
184 load->load = 0.0;
185 else
186 load->load = (load->runavg_delay - avgdel) / stddev;
187}
188
189
190/**
191 * Get the current load.
192 *
193 * @param load load handle
194 * @return zero for below-average load, otherwise
195 * number of std. devs we are above average;
196 * 100 if the latest updates were so large
197 * that we could not do proper calculations
198 */
199double
200GNUNET_LOAD_get_load (struct GNUNET_LOAD_Value *load)
201{
202 internal_update (load);
203 calculate_load (load);
204 return load->load;
205}
206
207
208/**
209 * Get the average value given to update so far.
210 *
211 * @param load load handle
212 * @return zero if update was never called
213 */
214double
215GNUNET_LOAD_get_average (struct GNUNET_LOAD_Value *load)
216{
217 double n;
218 double sum_val_i;
219
220 internal_update (load);
221 if (load->cummulative_request_count == 0)
222 return 0.0;
223 n = ((double) load->cummulative_request_count);
224 sum_val_i = (double) load->cummulative_delay;
225 return sum_val_i / n;
226}
227
228
229/**
230 * Update the current load.
231 *
232 * @param load to update
233 * @param data latest measurement value (for example, delay)
234 */
235void
236GNUNET_LOAD_update (struct GNUNET_LOAD_Value *load, uint64_t data)
237{
238 uint32_t dv;
239
240 internal_update (load);
241 load->last_update = GNUNET_TIME_absolute_get ();
242 if (data > 64 * 1024)
243 {
244 /* very large */
245 load->load = 100.0;
246 return;
247 }
248 dv = (uint32_t) data;
249 load->cummulative_delay += dv;
250 load->cummulative_squared_delay += dv * dv;
251 load->cummulative_request_count++;
252 load->runavg_delay = ((load->runavg_delay * 7.0) + dv) / 8.0;
253}
254
255
256/* end of load.c */
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