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/*
This file is part of GNUnet.
(C) 2010 Christian Grothoff (and other contributing authors)
GNUnet is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 2, or (at your
option) any later version.
GNUnet is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNUnet; see the file COPYING. If not, write to the
Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
*/
/**
* @file util/load.c
* @brief functions related to load calculations
* @author Christian Grothoff
*/
#include "platform.h"
#include "gnunet_load_lib.h"
#define DEBUG_LOAD GNUNET_NO
/**
* Values we track for load calculations.
*/
struct GNUNET_LOAD_Value
{
/**
* Sum of all datastore delays ever observed (in ms). Note that
* delays above 64k ms are excluded (to avoid overflow within
* first 4 billion requests).
*/
uint64_t cummulative_delay;
/**
* Sum of squares of all datastore delays ever observed (in ms). Note that
* delays above 64k ms are excluded (to avoid overflow within
* first 4 billion requests).
*/
uint64_t cummulative_squared_delay;
/**
* Total number of requests included in the cummulative datastore delay values.
*/
uint64_t cummulative_request_count;
/**
* Current running average datastore delay. Its relation to the
* average datastore delay and it std. dev. (as calcualted from the
* cummulative values) tells us our current load.
*/
double runavg_delay;
/**
* How high is the load? 0 for below average, otherwise
* the number of std. devs we are above average, or 100 if the
* load is so high that we currently cannot calculate it.
*/
double load;
};
/**
* Create a new load value.
*
* @return the new load value
*/
struct GNUNET_LOAD_Value *
GNUNET_LOAD_value_init ()
{
return GNUNET_malloc (sizeof (struct GNUNET_LOAD_Value));
}
/**
* Get the current load.
*
* @param load load handle
* @return zero for below-average load, otherwise
* number of std. devs we are above average;
* 100 if the latest updates were so large
* that we could not do proper calculations
*/
double
GNUNET_LOAD_get_load (const struct GNUNET_LOAD_Value *load)
{
return load->load;
}
/**
* Get the average value given to update so far.
*
* @param load load handle
* @return zero if update was never called
*/
double
GNUNET_LOAD_get_average (const struct GNUNET_LOAD_Value *load)
{
double n;
double avg;
double sum_val_i;
if (load->cummulative_request_count == 0)
return 0.0;
n = ((double) load->cummulative_request_count);
sum_val_i = (double) load->cummulative_delay;
return sum_val_i / n;
}
/**
* Update the current load.
*
* @param load to update
* @param data latest measurement value (for example, delay)
*/
void
GNUNET_LOAD_update (struct GNUNET_LOAD_Value *load,
uint64_t data)
{
uint32_t dv;
double stddev;
double avgdel;
double sum_val_i;
double n;
double nm1;
if (data > 64 * 1024)
{
/* very large */
load->load = 100.0;
return;
}
dv = (uint32_t) data;
load->cummulative_delay += dv;
load->cummulative_squared_delay += dv * dv;
load->cummulative_request_count++;
load->runavg_delay = ((load->runavg_delay * 7.0) + dv) / 8.0;
if (load->cummulative_request_count > 1)
{
/* calcuate std dev of latency; we have for n values of "i" that:
avg = (sum val_i) / n
stddev = (sum (val_i - avg)^2) / (n-1)
= (sum (val_i^2 - 2 avg val_i + avg^2) / (n-1)
= (sum (val_i^2) - 2 avg sum (val_i) + n * avg^2) / (n-1)
*/
sum_val_i = (double) load->cummulative_delay;
n = ((double) load->cummulative_request_count);
nm1 = n - 1.0;
avgdel = sum_val_i / n;
stddev = (((double) load->cummulative_squared_delay) - 2.0 * avgdel * sum_val_i + n * avgdel * avgdel) / nm1;
if (stddev <= 0)
stddev = 0.01; /* must have been rounding error or zero; prevent division by zero */
/* now calculate load based on how far out we are from
std dev; or if we are below average, simply assume load zero */
if (load->runavg_delay < avgdel)
load->load = 0.0;
else
load->load = (load->runavg_delay - avgdel) / stddev;
}
}
/* end of load.c */
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