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18 * @brief functions related to load calculations
19 * @author Christian Grothoff
22 #include "gnunet_util_lib.h"
25 #define LOG(kind,...) GNUNET_log_from (kind, "util-load", __VA_ARGS__)
28 * Values we track for load calculations.
30 struct GNUNET_LOAD_Value
34 * How fast should the load decline if no values are added?
36 struct GNUNET_TIME_Relative autodecline;
39 * Last time this load value was updated by an event.
41 struct GNUNET_TIME_Absolute last_update;
44 * Sum of all datastore delays ever observed (in ms). Note that
45 * delays above 64k ms are excluded (to avoid overflow within
46 * first 4 billion requests).
48 uint64_t cummulative_delay;
51 * Sum of squares of all datastore delays ever observed (in ms). Note that
52 * delays above 64k ms are excluded (to avoid overflow within
53 * first 4 billion requests).
55 uint64_t cummulative_squared_delay;
58 * Total number of requests included in the cummulative datastore delay values.
60 uint64_t cummulative_request_count;
63 * Current running average datastore delay. Its relation to the
64 * average datastore delay and it std. dev. (as calcualted from the
65 * cummulative values) tells us our current load.
70 * How high is the load? 0 for below average, otherwise
71 * the number of std. devs we are above average, or 100 if the
72 * load is so high that we currently cannot calculate it.
80 internal_update (struct GNUNET_LOAD_Value *load)
82 struct GNUNET_TIME_Relative delta;
85 if (load->autodecline.rel_value_us == GNUNET_TIME_UNIT_FOREVER_REL.rel_value_us)
87 delta = GNUNET_TIME_absolute_get_duration (load->last_update);
88 if (delta.rel_value_us < load->autodecline.rel_value_us)
90 if (0 == load->autodecline.rel_value_us)
92 load->runavg_delay = 0.0;
96 n = delta.rel_value_us / load->autodecline.rel_value_us;
99 load->runavg_delay = 0.0;
106 load->runavg_delay = (load->runavg_delay * 7.0) / 8.0;
112 * Create a new load value.
114 * @param autodecline speed at which this value should automatically
115 * decline in the absence of external events; at the given
116 * frequency, 0-load values will be added to the load
117 * @return the new load value
119 struct GNUNET_LOAD_Value *
120 GNUNET_LOAD_value_init (struct GNUNET_TIME_Relative autodecline)
122 struct GNUNET_LOAD_Value *ret;
124 ret = GNUNET_new (struct GNUNET_LOAD_Value);
125 ret->autodecline = autodecline;
126 ret->last_update = GNUNET_TIME_absolute_get ();
132 * Change the value by which the load automatically declines.
134 * @param load load to update
135 * @param autodecline frequency of load decline
138 GNUNET_LOAD_value_set_decline (struct GNUNET_LOAD_Value *load,
139 struct GNUNET_TIME_Relative autodecline)
141 internal_update (load);
142 load->autodecline = autodecline;
147 * Recalculate our load value.
149 * @param load load to update
152 calculate_load (struct GNUNET_LOAD_Value *load)
160 if (load->cummulative_request_count <= 1)
162 /* calcuate std dev of latency; we have for n values of "i" that:
164 * avg = (sum val_i) / n
165 * stddev = (sum (val_i - avg)^2) / (n-1)
166 * = (sum (val_i^2 - 2 avg val_i + avg^2) / (n-1)
167 * = (sum (val_i^2) - 2 avg sum (val_i) + n * avg^2) / (n-1)
169 sum_val_i = (double) load->cummulative_delay;
170 n = ((double) load->cummulative_request_count);
172 avgdel = sum_val_i / n;
174 (((double) load->cummulative_squared_delay) - 2.0 * avgdel * sum_val_i +
175 n * avgdel * avgdel) / nm1;
177 stddev = 0.01; /* must have been rounding error or zero; prevent division by zero */
178 /* now calculate load based on how far out we are from
179 * std dev; or if we are below average, simply assume load zero */
180 if (load->runavg_delay < avgdel)
183 load->load = (load->runavg_delay - avgdel) / stddev;
188 * Get the current load.
190 * @param load load handle
191 * @return zero for below-average load, otherwise
192 * number of std. devs we are above average;
193 * 100 if the latest updates were so large
194 * that we could not do proper calculations
197 GNUNET_LOAD_get_load (struct GNUNET_LOAD_Value *load)
199 internal_update (load);
200 calculate_load (load);
206 * Get the average value given to update so far.
208 * @param load load handle
209 * @return zero if update was never called
212 GNUNET_LOAD_get_average (struct GNUNET_LOAD_Value *load)
217 internal_update (load);
218 if (load->cummulative_request_count == 0)
220 n = ((double) load->cummulative_request_count);
221 sum_val_i = (double) load->cummulative_delay;
222 return sum_val_i / n;
227 * Update the current load.
229 * @param load to update
230 * @param data latest measurement value (for example, delay)
233 GNUNET_LOAD_update (struct GNUNET_LOAD_Value *load, uint64_t data)
237 internal_update (load);
238 load->last_update = GNUNET_TIME_absolute_get ();
239 if (data > 64 * 1024)
245 dv = (uint32_t) data;
246 load->cummulative_delay += dv;
247 load->cummulative_squared_delay += dv * dv;
248 load->cummulative_request_count++;
249 load->runavg_delay = ((load->runavg_delay * 7.0) + dv) / 8.0;