+++ /dev/null
-/**
- * collectd - src/utils_latency.c
- * Copyright (C) 2013 Florian Forster
- *
- * Permission is hereby granted, free of charge, to any person obtaining a
- * copy of this software and associated documentation files (the "Software"),
- * to deal in the Software without restriction, including without limitation
- * the rights to use, copy, modify, merge, publish, distribute, sublicense,
- * and/or sell copies of the Software, and to permit persons to whom the
- * Software is furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
- * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
- * DEALINGS IN THE SOFTWARE.
- *
- * Authors:
- * Florian Forster <ff at octo.it>
- **/
-
-#include "collectd.h"
-
-#include "common.h"
-#include "plugin.h"
-#include "utils_latency.h"
-
-#include <limits.h>
-#include <math.h>
-
-#ifndef LLONG_MAX
-#define LLONG_MAX 9223372036854775807LL
-#endif
-
-#ifndef HISTOGRAM_DEFAULT_BIN_WIDTH
-/* 1048576 = 2^20 ^= 1/1024 s */
-#define HISTOGRAM_DEFAULT_BIN_WIDTH 1048576
-#endif
-
-struct latency_counter_s {
- cdtime_t start_time;
-
- cdtime_t sum;
- size_t num;
-
- cdtime_t min;
- cdtime_t max;
-
- cdtime_t bin_width;
- int histogram[HISTOGRAM_NUM_BINS];
-};
-
-/*
-* Histogram represents the distribution of data, it has a list of "bins".
-* Each bin represents an interval and has a count (frequency) of
-* number of values fall within its interval.
-*
-* Histogram's range is determined by the number of bins and the bin width,
-* There are 1000 bins and all bins have the same width of default 1 millisecond.
-* When a value above this range is added, Histogram's range is increased by
-* increasing the bin width (note that number of bins remains always at 1000).
-* This operation of increasing bin width is little expensive as each bin need
-* to be visited to update it's count. To reduce frequent change of bin width,
-* new bin width will be the next nearest power of 2. Example: 2, 4, 8, 16, 32,
-* 64, 128, 256, 512, 1024, 2048, 5086, ...
-*
-* So, if the required bin width is 300, then new bin width will be 512 as it is
-* the next nearest power of 2.
-*/
-static void change_bin_width(latency_counter_t *lc, cdtime_t latency) /* {{{ */
-{
- /* This function is called because the new value is above histogram's range.
- * First find the required bin width:
- * requiredBinWidth = (value + 1) / numBins
- * then get the next nearest power of 2
- * newBinWidth = 2^(ceil(log2(requiredBinWidth)))
- */
- double required_bin_width =
- ((double)(latency + 1)) / ((double)HISTOGRAM_NUM_BINS);
- double required_bin_width_logbase2 = log(required_bin_width) / log(2.0);
- cdtime_t new_bin_width =
- (cdtime_t)(pow(2.0, ceil(required_bin_width_logbase2)) + .5);
- cdtime_t old_bin_width = lc->bin_width;
-
- lc->bin_width = new_bin_width;
-
- /* bin_width has been increased, now iterate through all bins and move the
- * old bin's count to new bin. */
- if (lc->num > 0) // if the histogram has data then iterate else skip
- {
- double width_change_ratio =
- ((double)old_bin_width) / ((double)new_bin_width);
-
- for (size_t i = 0; i < HISTOGRAM_NUM_BINS; i++) {
- size_t new_bin = (size_t)(((double)i) * width_change_ratio);
- if (i == new_bin)
- continue;
- assert(new_bin < i);
-
- lc->histogram[new_bin] += lc->histogram[i];
- lc->histogram[i] = 0;
- }
- }
-
- DEBUG("utils_latency: change_bin_width: latency = %.3f; "
- "old_bin_width = %.3f; new_bin_width = %.3f;",
- CDTIME_T_TO_DOUBLE(latency), CDTIME_T_TO_DOUBLE(old_bin_width),
- CDTIME_T_TO_DOUBLE(new_bin_width));
-} /* }}} void change_bin_width */
-
-latency_counter_t *latency_counter_create(void) /* {{{ */
-{
- latency_counter_t *lc;
-
- lc = calloc(1, sizeof(*lc));
- if (lc == NULL)
- return (NULL);
-
- lc->bin_width = HISTOGRAM_DEFAULT_BIN_WIDTH;
- latency_counter_reset(lc);
- return (lc);
-} /* }}} latency_counter_t *latency_counter_create */
-
-void latency_counter_destroy(latency_counter_t *lc) /* {{{ */
-{
- sfree(lc);
-} /* }}} void latency_counter_destroy */
-
-void latency_counter_add(latency_counter_t *lc, cdtime_t latency) /* {{{ */
-{
- cdtime_t bin;
-
- if ((lc == NULL) || (latency == 0) || (latency > ((cdtime_t)LLONG_MAX)))
- return;
-
- lc->sum += latency;
- lc->num++;
-
- if ((lc->min == 0) && (lc->max == 0))
- lc->min = lc->max = latency;
- if (lc->min > latency)
- lc->min = latency;
- if (lc->max < latency)
- lc->max = latency;
-
- /* A latency of _exactly_ 1.0 ms is stored in the buffer 0, so
- * subtract one from the cdtime_t value so that exactly 1.0 ms get sorted
- * accordingly. */
- bin = (latency - 1) / lc->bin_width;
- if (bin >= HISTOGRAM_NUM_BINS) {
- change_bin_width(lc, latency);
- bin = (latency - 1) / lc->bin_width;
- if (bin >= HISTOGRAM_NUM_BINS) {
- ERROR("utils_latency: latency_counter_add: Invalid bin: %" PRIu64, bin);
- return;
- }
- }
- lc->histogram[bin]++;
-} /* }}} void latency_counter_add */
-
-void latency_counter_reset(latency_counter_t *lc) /* {{{ */
-{
- if (lc == NULL)
- return;
-
- cdtime_t bin_width = lc->bin_width;
- cdtime_t max_bin = (lc->max - 1) / lc->bin_width;
-
-/*
- If max latency is REDUCE_THRESHOLD times less than histogram's range,
- then cut it in half. REDUCE_THRESHOLD must be >= 2.
- Value of 4 is selected to reduce frequent changes of bin width.
-*/
-#define REDUCE_THRESHOLD 4
- if ((lc->num > 0) && (lc->bin_width >= HISTOGRAM_DEFAULT_BIN_WIDTH * 2) &&
- (max_bin < HISTOGRAM_NUM_BINS / REDUCE_THRESHOLD)) {
- /* new bin width will be the previous power of 2 */
- bin_width = bin_width / 2;
-
- DEBUG("utils_latency: latency_counter_reset: max_latency = %.3f; "
- "max_bin = %" PRIu64 "; old_bin_width = %.3f; new_bin_width = %.3f;",
- CDTIME_T_TO_DOUBLE(lc->max), max_bin,
- CDTIME_T_TO_DOUBLE(lc->bin_width), CDTIME_T_TO_DOUBLE(bin_width));
- }
-
- memset(lc, 0, sizeof(*lc));
-
- /* preserve bin width */
- lc->bin_width = bin_width;
- lc->start_time = cdtime();
-} /* }}} void latency_counter_reset */
-
-cdtime_t latency_counter_get_min(latency_counter_t *lc) /* {{{ */
-{
- if (lc == NULL)
- return (0);
- return (lc->min);
-} /* }}} cdtime_t latency_counter_get_min */
-
-cdtime_t latency_counter_get_max(latency_counter_t *lc) /* {{{ */
-{
- if (lc == NULL)
- return (0);
- return (lc->max);
-} /* }}} cdtime_t latency_counter_get_max */
-
-cdtime_t latency_counter_get_sum(latency_counter_t *lc) /* {{{ */
-{
- if (lc == NULL)
- return (0);
- return (lc->sum);
-} /* }}} cdtime_t latency_counter_get_sum */
-
-size_t latency_counter_get_num(latency_counter_t *lc) /* {{{ */
-{
- if (lc == NULL)
- return (0);
- return (lc->num);
-} /* }}} size_t latency_counter_get_num */
-
-cdtime_t latency_counter_get_average(latency_counter_t *lc) /* {{{ */
-{
- double average;
-
- if ((lc == NULL) || (lc->num == 0))
- return (0);
-
- average = CDTIME_T_TO_DOUBLE(lc->sum) / ((double)lc->num);
- return (DOUBLE_TO_CDTIME_T(average));
-} /* }}} cdtime_t latency_counter_get_average */
-
-cdtime_t latency_counter_get_percentile(latency_counter_t *lc, /* {{{ */
- double percent) {
- double percent_upper;
- double percent_lower;
- double p;
- cdtime_t latency_lower;
- cdtime_t latency_interpolated;
- int sum;
- size_t i;
-
- if ((lc == NULL) || (lc->num == 0) || !((percent > 0.0) && (percent < 100.0)))
- return (0);
-
- /* Find index i so that at least "percent" events are within i+1 ms. */
- percent_upper = 0.0;
- percent_lower = 0.0;
- sum = 0;
- for (i = 0; i < HISTOGRAM_NUM_BINS; i++) {
- percent_lower = percent_upper;
- sum += lc->histogram[i];
- if (sum == 0)
- percent_upper = 0.0;
- else
- percent_upper = 100.0 * ((double)sum) / ((double)lc->num);
-
- if (percent_upper >= percent)
- break;
- }
-
- if (i >= HISTOGRAM_NUM_BINS)
- return (0);
-
- assert(percent_upper >= percent);
- assert(percent_lower < percent);
-
- if (i == 0)
- return (lc->bin_width);
-
- latency_lower = ((cdtime_t)i) * lc->bin_width;
- p = (percent - percent_lower) / (percent_upper - percent_lower);
-
- latency_interpolated =
- latency_lower + DOUBLE_TO_CDTIME_T(p * CDTIME_T_TO_DOUBLE(lc->bin_width));
-
- DEBUG("latency_counter_get_percentile: latency_interpolated = %.3f",
- CDTIME_T_TO_DOUBLE(latency_interpolated));
- return (latency_interpolated);
-} /* }}} cdtime_t latency_counter_get_percentile */
-
-double latency_counter_get_rate(const latency_counter_t *lc, /* {{{ */
- cdtime_t lower, cdtime_t upper,
- const cdtime_t now) {
- if ((lc == NULL) || (lc->num == 0))
- return (NAN);
-
- if (upper && (upper < lower))
- return (NAN);
- if (lower == upper)
- return (0);
-
- /* Buckets have an exclusive lower bound and an inclusive upper bound. That
- * means that the first bucket, index 0, represents (0-bin_width]. That means
- * that latency==bin_width needs to result in bin=0, that's why we need to
- * subtract one before dividing by bin_width. */
- cdtime_t lower_bin = 0;
- if (lower)
- /* lower is *exclusive* => determine bucket for lower+1 */
- lower_bin = ((lower + 1) - 1) / lc->bin_width;
-
- /* lower is greater than the longest latency observed => rate is zero. */
- if (lower_bin >= HISTOGRAM_NUM_BINS)
- return (0);
-
- cdtime_t upper_bin = HISTOGRAM_NUM_BINS - 1;
- if (upper)
- upper_bin = (upper - 1) / lc->bin_width;
-
- if (upper_bin >= HISTOGRAM_NUM_BINS) {
- upper_bin = HISTOGRAM_NUM_BINS - 1;
- upper = 0;
- }
-
- double sum = 0;
- for (size_t i = lower_bin; i <= upper_bin; i++)
- sum += lc->histogram[i];
-
- if (lower) {
- /* Approximate ratio of requests in lower_bin, that fall between
- * lower_bin_boundary and lower. This ratio is then subtracted from sum to
- * increase accuracy. */
- cdtime_t lower_bin_boundary = lower_bin * lc->bin_width;
- assert(lower >= lower_bin_boundary);
- double lower_ratio =
- (double)(lower - lower_bin_boundary) / ((double)lc->bin_width);
- sum -= lower_ratio * lc->histogram[lower_bin];
- }
-
- if (upper) {
- /* As above: approximate ratio of requests in upper_bin, that fall between
- * upper and upper_bin_boundary. */
- cdtime_t upper_bin_boundary = (upper_bin + 1) * lc->bin_width;
- assert(upper <= upper_bin_boundary);
- double ratio = (double)(upper_bin_boundary - upper) / (double)lc->bin_width;
- sum -= ratio * lc->histogram[upper_bin];
- }
-
- return sum / (CDTIME_T_TO_DOUBLE(now - lc->start_time));
-} /* }}} double latency_counter_get_rate */
-
-/* vim: set sw=2 sts=2 et fdm=marker : */
projects / collectd.git / blobdiff