X-Git-Url: https://git.verplant.org/?a=blobdiff_plain;f=src%2Futils_latency.c;h=5749f10da199700c0b18e0c36020e6f2f9c072a1;hb=936c450a86c841eea89888c8550c9118fae90c25;hp=dfdef6115f249f1c9f66a74467192a667e94a325;hpb=51612a1b2f96f6e360f874f6da0b20eac94f48b3;p=collectd.git diff --git a/src/utils_latency.c b/src/utils_latency.c index dfdef611..5749f10d 100644 --- a/src/utils_latency.c +++ b/src/utils_latency.c @@ -1,6 +1,6 @@ /** * collectd - src/utils_latency.c - * Copyright (C) 2013 Florian Forster + * 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"), @@ -25,17 +25,22 @@ **/ #include "collectd.h" + #include "plugin.h" #include "utils_latency.h" #include "common.h" #include +#include -#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 { @@ -47,7 +52,7 @@ struct latency_counter_s cdtime_t min; cdtime_t max; - int bin_width; + cdtime_t bin_width; int histogram[HISTOGRAM_NUM_BINS]; }; @@ -67,59 +72,57 @@ struct latency_counter_s * * 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_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; + 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. - */ + /* 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; ihistogram[new_bin] += lc->histogram[i]; lc->histogram[i] = 0; } - DEBUG("utils_latency: change_bin_width: fixed all bins"); } - 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); - latency_counter_reset (lc); lc->bin_width = HISTOGRAM_DEFAULT_BIN_WIDTH; + latency_counter_reset (lc); return (lc); } /* }}} latency_counter_t *latency_counter_create */ @@ -130,9 +133,9 @@ void latency_counter_destroy (latency_counter_t *lc) /* {{{ */ 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; @@ -145,19 +148,17 @@ void latency_counter_add (latency_counter_t *lc, cdtime_t 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); + bin = (latency - 1) / lc->bin_width; if (bin >= HISTOGRAM_NUM_BINS) { - change_bin_width(lc, latency_ms); - bin = (int)(latency_ms / lc->bin_width); + change_bin_width (lc, latency); + bin = (latency - 1) / lc->bin_width; if (bin >= HISTOGRAM_NUM_BINS) { - ERROR("utils_latency: latency_counter_add: Invalid bin %d", bin); + ERROR ("utils_latency: latency_counter_add: Invalid bin: %"PRIu64, bin); return; } } @@ -169,7 +170,29 @@ void latency_counter_reset (latency_counter_t *lc) /* {{{ */ if (lc == NULL) return; - int bin_width = lc->bin_width; + 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 */ @@ -216,14 +239,14 @@ cdtime_t latency_counter_get_average (latency_counter_t *lc) /* {{{ */ return (DOUBLE_TO_CDTIME_T (average)); } /* }}} cdtime_t latency_counter_get_average */ -cdtime_t latency_counter_get_percentile (latency_counter_t *lc, +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; @@ -253,16 +276,78 @@ cdtime_t latency_counter_get_percentile (latency_counter_t *lc, 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 : */