**/
#include "collectd.h"
+
+#include "common.h"
#include "plugin.h"
#include "utils_latency.h"
-#include "common.h"
+#include <limits.h>
#include <math.h>
-#ifndef HISTOGRAM_NUM_BINS
-# define HISTOGRAM_NUM_BINS 1000
+#ifndef LLONG_MAX
+#define LLONG_MAX 9223372036854775807LL
#endif
-static const int HISTOGRAM_DEFAULT_BIN_WIDTH = 1;
+#ifndef HISTOGRAM_DEFAULT_BIN_WIDTH
+/* 1048576 = 2^20 ^= 1/1024 s */
+#define HISTOGRAM_DEFAULT_BIN_WIDTH 1048576
+#endif
-struct latency_counter_s
-{
+struct latency_counter_s {
cdtime_t start_time;
cdtime_t sum;
cdtime_t min;
cdtime_t max;
- int bin_width;
+ cdtime_t bin_width;
int histogram[HISTOGRAM_NUM_BINS];
};
*
* So, if the required bin width is 300, then new bin width will be 512 as it is
* the next nearest power of 2.
-*
*/
-void change_bin_width (latency_counter_t *lc, size_t val) /* {{{ */
+static void change_bin_width(latency_counter_t *lc, cdtime_t latency) /* {{{ */
{
- int i=0;
/* 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)(val + 1) / HISTOGRAM_NUM_BINS;
+ double required_bin_width =
+ ((double)(latency + 1)) / ((double)HISTOGRAM_NUM_BINS);
double required_bin_width_logbase2 = log(required_bin_width) / log(2.0);
- int new_bin_width = (int)(pow(2.0, ceil( required_bin_width_logbase2)));
- int old_bin_width = lc->bin_width;
+ 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.
- */
+ /* 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 = old_bin_width / new_bin_width;
- for (i=0; i<HISTOGRAM_NUM_BINS; i++)
- {
- int new_bin = (int)(i * width_change_ratio);
- if (i == new_bin)
- continue;
- lc->histogram[new_bin] += lc->histogram[i];
- lc->histogram[i] = 0;
- }
- DEBUG("utils_latency: change_bin_width: fixed all bins");
+ 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: val-[%zu], oldBinWidth-[%d], "
- "newBinWidth-[%d], required_bin_width-[%f], "
- "required_bin_width_logbase2-[%f]",
- val, old_bin_width, new_bin_width, required_bin_width,
- required_bin_width_logbase2);
-
+ 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 () /* {{{ */
+latency_counter_t *latency_counter_create(void) /* {{{ */
{
latency_counter_t *lc;
- lc = malloc (sizeof (*lc));
+ lc = calloc(1, sizeof(*lc));
if (lc == NULL)
return (NULL);
- memset (lc, 0, sizeof (*lc));
- latency_counter_reset (lc);
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) /* {{{ */
+void latency_counter_destroy(latency_counter_t *lc) /* {{{ */
{
- sfree (lc);
+ sfree(lc);
} /* }}} void latency_counter_destroy */
-void latency_counter_add (latency_counter_t *lc, cdtime_t latency) /* {{{ */
+void latency_counter_add(latency_counter_t *lc, cdtime_t latency) /* {{{ */
{
- size_t latency_ms;
+ cdtime_t bin;
- if ((lc == NULL) || (latency == 0))
+ if ((lc == NULL) || (latency == 0) || (latency > ((cdtime_t)LLONG_MAX)))
return;
lc->sum += latency;
if (lc->max < latency)
lc->max = latency;
- /* A latency of _exactly_ 1.0 ms should be stored in the buffer 0, so
+ /* 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. */
- latency_ms = (size_t) CDTIME_T_TO_MS (latency - 1);
-
- int bin = (int)(latency_ms / lc->bin_width);
- if (bin >= HISTOGRAM_NUM_BINS)
- {
- change_bin_width(lc, latency_ms);
- bin = (int)(latency_ms / lc->bin_width);
- if (bin >= HISTOGRAM_NUM_BINS)
- {
- ERROR("utils_latency: latency_counter_add: Invalid bin %d", bin);
- return;
- }
+ 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) /* {{{ */
+void latency_counter_reset(latency_counter_t *lc) /* {{{ */
{
if (lc == NULL)
return;
- int bin_width = lc->bin_width;
- memset (lc, 0, sizeof (*lc));
+ 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 ();
+ lc->start_time = cdtime();
} /* }}} void latency_counter_reset */
-cdtime_t latency_counter_get_min (latency_counter_t *lc) /* {{{ */
+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) /* {{{ */
+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) /* {{{ */
+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) /* {{{ */
+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) /* {{{ */
+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));
+ 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)
-{
+cdtime_t latency_counter_get_percentile(latency_counter_t *lc, /* {{{ */
+ double percent) {
double percent_upper;
double percent_lower;
- double ms_upper;
- double ms_lower;
- double ms_interpolated;
+ double p;
+ cdtime_t latency_lower;
+ cdtime_t latency_interpolated;
int sum;
size_t i;
percent_upper = 0.0;
percent_lower = 0.0;
sum = 0;
- for (i = 0; i < HISTOGRAM_NUM_BINS; i++)
- {
+ 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);
+ 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);
+ assert(percent_upper >= percent);
+ assert(percent_lower < percent);
- ms_upper = (double) ( (i + 1) * lc->bin_width );
- ms_lower = (double) ( i * lc->bin_width );
if (i == 0)
- return (MS_TO_CDTIME_T (ms_upper));
+ return (lc->bin_width);
- ms_interpolated = (((percent_upper - percent) * ms_lower)
- + ((percent - percent_lower) * ms_upper))
- / (percent_upper - percent_lower);
+ latency_lower = ((cdtime_t)i) * lc->bin_width;
+ p = (percent - percent_lower) / (percent_upper - percent_lower);
- return (MS_TO_CDTIME_T (ms_interpolated));
+ 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 : */