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/*
*
* Copyright 2015 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
#include "test/core/util/histogram.h"
#include <math.h>
#include <stddef.h>
#include <string.h>
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/port_platform.h>
#include "src/core/lib/gpr/useful.h"
/* Histograms are stored with exponentially increasing bucket sizes.
The first bucket is [0, m) where m = 1 + resolution
Bucket n (n>=1) contains [m**n, m**(n+1))
There are sufficient buckets to reach max_bucket_start */
struct grpc_histogram {
/* Sum of all values seen so far */
double sum;
/* Sum of squares of all values seen so far */
double sum_of_squares;
/* number of values seen so far */
double count;
/* m in the description */
double multiplier;
double one_on_log_multiplier;
/* minimum value seen */
double min_seen;
/* maximum value seen */
double max_seen;
/* maximum representable value */
double max_possible;
/* number of buckets */
size_t num_buckets;
/* the buckets themselves */
uint32_t* buckets;
};
/* determine a bucket index given a value - does no bounds checking */
static size_t bucket_for_unchecked(grpc_histogram* h, double x) {
return static_cast<size_t>(log(x) * h->one_on_log_multiplier);
}
/* bounds checked version of the above */
static size_t bucket_for(grpc_histogram* h, double x) {
size_t bucket = bucket_for_unchecked(h, GPR_CLAMP(x, 1.0, h->max_possible));
GPR_ASSERT(bucket < h->num_buckets);
return bucket;
}
/* at what value does a bucket start? */
static double bucket_start(grpc_histogram* h, double x) {
return pow(h->multiplier, x);
}
grpc_histogram* grpc_histogram_create(double resolution,
double max_bucket_start) {
grpc_histogram* h =
static_cast<grpc_histogram*>(gpr_malloc(sizeof(grpc_histogram)));
GPR_ASSERT(resolution > 0.0);
GPR_ASSERT(max_bucket_start > resolution);
h->sum = 0.0;
h->sum_of_squares = 0.0;
h->multiplier = 1.0 + resolution;
h->one_on_log_multiplier = 1.0 / log(1.0 + resolution);
h->max_possible = max_bucket_start;
h->count = 0.0;
h->min_seen = max_bucket_start;
h->max_seen = 0.0;
h->num_buckets = bucket_for_unchecked(h, max_bucket_start) + 1;
GPR_ASSERT(h->num_buckets > 1);
GPR_ASSERT(h->num_buckets < 100000000);
h->buckets =
static_cast<uint32_t*>(gpr_zalloc(sizeof(uint32_t) * h->num_buckets));
return h;
}
void grpc_histogram_destroy(grpc_histogram* h) {
gpr_free(h->buckets);
gpr_free(h);
}
void grpc_histogram_add(grpc_histogram* h, double x) {
h->sum += x;
h->sum_of_squares += x * x;
h->count++;
if (x < h->min_seen) {
h->min_seen = x;
}
if (x > h->max_seen) {
h->max_seen = x;
}
h->buckets[bucket_for(h, x)]++;
}
int grpc_histogram_merge(grpc_histogram* dst, const grpc_histogram* src) {
if ((dst->num_buckets != src->num_buckets) ||
(dst->multiplier != src->multiplier)) {
/* Fail because these histograms don't match */
return 0;
}
grpc_histogram_merge_contents(dst, src->buckets, src->num_buckets,
src->min_seen, src->max_seen, src->sum,
src->sum_of_squares, src->count);
return 1;
}
void grpc_histogram_merge_contents(grpc_histogram* histogram,
const uint32_t* data, size_t data_count,
double min_seen, double max_seen, double sum,
double sum_of_squares, double count) {
size_t i;
GPR_ASSERT(histogram->num_buckets == data_count);
histogram->sum += sum;
histogram->sum_of_squares += sum_of_squares;
histogram->count += count;
if (min_seen < histogram->min_seen) {
histogram->min_seen = min_seen;
}
if (max_seen > histogram->max_seen) {
histogram->max_seen = max_seen;
}
for (i = 0; i < histogram->num_buckets; i++) {
histogram->buckets[i] += data[i];
}
}
static double threshold_for_count_below(grpc_histogram* h, double count_below) {
double count_so_far;
double lower_bound;
double upper_bound;
size_t lower_idx;
size_t upper_idx;
if (h->count == 0) {
return 0.0;
}
if (count_below <= 0) {
return h->min_seen;
}
if (count_below >= h->count) {
return h->max_seen;
}
/* find the lowest bucket that gets us above count_below */
count_so_far = 0.0;
for (lower_idx = 0; lower_idx < h->num_buckets; lower_idx++) {
count_so_far += h->buckets[lower_idx];
if (count_so_far >= count_below) {
break;
}
}
if (count_so_far == count_below) {
/* this bucket hits the threshold exactly... we should be midway through
any run of zero values following the bucket */
for (upper_idx = lower_idx + 1; upper_idx < h->num_buckets; upper_idx++) {
if (h->buckets[upper_idx]) {
break;
}
}
return (bucket_start(h, static_cast<double>(lower_idx)) +
bucket_start(h, static_cast<double>(upper_idx))) /
2.0;
} else {
/* treat values as uniform throughout the bucket, and find where this value
should lie */
lower_bound = bucket_start(h, static_cast<double>(lower_idx));
upper_bound = bucket_start(h, static_cast<double>(lower_idx + 1));
return GPR_CLAMP(upper_bound - (upper_bound - lower_bound) *
(count_so_far - count_below) /
h->buckets[lower_idx],
h->min_seen, h->max_seen);
}
}
double grpc_histogram_percentile(grpc_histogram* h, double percentile) {
return threshold_for_count_below(h, h->count * percentile / 100.0);
}
double grpc_histogram_mean(grpc_histogram* h) {
GPR_ASSERT(h->count != 0);
return h->sum / h->count;
}
double grpc_histogram_stddev(grpc_histogram* h) {
return sqrt(grpc_histogram_variance(h));
}
double grpc_histogram_variance(grpc_histogram* h) {
if (h->count == 0) return 0.0;
return (h->sum_of_squares * h->count - h->sum * h->sum) /
(h->count * h->count);
}
double grpc_histogram_maximum(grpc_histogram* h) { return h->max_seen; }
double grpc_histogram_minimum(grpc_histogram* h) { return h->min_seen; }
double grpc_histogram_count(grpc_histogram* h) { return h->count; }
double grpc_histogram_sum(grpc_histogram* h) { return h->sum; }
double grpc_histogram_sum_of_squares(grpc_histogram* h) {
return h->sum_of_squares;
}
const uint32_t* grpc_histogram_get_contents(grpc_histogram* histogram,
size_t* count) {
*count = histogram->num_buckets;
return histogram->buckets;
}
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