2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
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23 * @brief functions related to load calculations
24 * @author Christian Grothoff
27 #include "gnunet_load_lib.h"
29 #define DEBUG_LOAD GNUNET_NO
32 * Values we track for load calculations.
34 struct GNUNET_LOAD_Value
38 * How fast should the load decline if no values are added?
40 struct GNUNET_TIME_Relative autodecline;
43 * Last time this load value was updated by an event.
45 struct GNUNET_TIME_Absolute last_update;
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).
52 uint64_t cummulative_delay;
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).
59 uint64_t cummulative_squared_delay;
62 * Total number of requests included in the cummulative datastore delay values.
64 uint64_t cummulative_request_count;
67 * Current running average datastore delay. Its relation to the
68 * average datastore delay and it std. dev. (as calcualted from the
69 * cummulative values) tells us our current load.
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.
84 internal_update (struct GNUNET_LOAD_Value *load)
86 struct GNUNET_TIME_Relative delta;
89 if (load->autodecline.rel_value == GNUNET_TIME_UNIT_FOREVER_REL.rel_value)
91 delta = GNUNET_TIME_absolute_get_duration (load->last_update);
92 if (delta.rel_value < load->autodecline.rel_value)
94 if (load->autodecline.rel_value == 0)
96 load->runavg_delay = 0.0;
100 n = delta.rel_value / load->autodecline.rel_value;
103 load->runavg_delay = 0.0;
110 load->runavg_delay = (load->runavg_delay * 7.0) / 8.0;
116 * Create a new load value.
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
123 struct GNUNET_LOAD_Value *
124 GNUNET_LOAD_value_init (struct GNUNET_TIME_Relative autodecline)
126 struct GNUNET_LOAD_Value *ret;
128 ret = GNUNET_malloc (sizeof (struct GNUNET_LOAD_Value));
129 ret->autodecline = autodecline;
130 ret->last_update = GNUNET_TIME_absolute_get ();
136 * Change the value by which the load automatically declines.
138 * @param load load to update
139 * @param autodecline frequency of load decline
142 GNUNET_LOAD_value_set_decline (struct GNUNET_LOAD_Value *load,
143 struct GNUNET_TIME_Relative autodecline)
145 internal_update (load);
146 load->autodecline = autodecline;
151 * Recalculate our load value.
153 * @param load load to update
156 calculate_load (struct GNUNET_LOAD_Value *load)
164 if (load->cummulative_request_count <= 1)
166 /* calcuate std dev of latency; we have for n values of "i" that:
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)
173 sum_val_i = (double) load->cummulative_delay;
174 n = ((double) load->cummulative_request_count);
176 avgdel = sum_val_i / n;
178 (((double) load->cummulative_squared_delay) - 2.0 * avgdel * sum_val_i +
179 n * avgdel * avgdel) / nm1;
181 stddev = 0.01; /* must have been rounding error or zero; prevent division by zero */
182 /* now calculate load based on how far out we are from
183 * std dev; or if we are below average, simply assume load zero */
184 if (load->runavg_delay < avgdel)
187 load->load = (load->runavg_delay - avgdel) / stddev;
192 * Get the current load.
194 * @param load load handle
195 * @return zero for below-average load, otherwise
196 * number of std. devs we are above average;
197 * 100 if the latest updates were so large
198 * that we could not do proper calculations
201 GNUNET_LOAD_get_load (struct GNUNET_LOAD_Value *load)
203 internal_update (load);
204 calculate_load (load);
210 * Get the average value given to update so far.
212 * @param load load handle
213 * @return zero if update was never called
216 GNUNET_LOAD_get_average (struct GNUNET_LOAD_Value *load)
221 internal_update (load);
222 if (load->cummulative_request_count == 0)
224 n = ((double) load->cummulative_request_count);
225 sum_val_i = (double) load->cummulative_delay;
226 return sum_val_i / n;
231 * Update the current load.
233 * @param load to update
234 * @param data latest measurement value (for example, delay)
237 GNUNET_LOAD_update (struct GNUNET_LOAD_Value *load, uint64_t data)
241 internal_update (load);
242 load->last_update = GNUNET_TIME_absolute_get ();
243 if (data > 64 * 1024)
249 dv = (uint32_t) data;
250 load->cummulative_delay += dv;
251 load->cummulative_squared_delay += dv * dv;
252 load->cummulative_request_count++;
253 load->runavg_delay = ((load->runavg_delay * 7.0) + dv) / 8.0;