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1 /*
2  *
3  * Copyright 2015 gRPC authors.
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  *     http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  *
17  */
18 
19 #include "test/core/util/histogram.h"
20 
21 #include <math.h>
22 #include <stddef.h>
23 #include <string.h>
24 
25 #include <grpc/support/alloc.h>
26 #include <grpc/support/log.h>
27 #include <grpc/support/port_platform.h>
28 
29 #include "src/core/lib/gpr/useful.h"
30 
31 /* Histograms are stored with exponentially increasing bucket sizes.
32    The first bucket is [0, m) where m = 1 + resolution
33    Bucket n (n>=1) contains [m**n, m**(n+1))
34    There are sufficient buckets to reach max_bucket_start */
35 
36 struct grpc_histogram {
37   /* Sum of all values seen so far */
38   double sum;
39   /* Sum of squares of all values seen so far */
40   double sum_of_squares;
41   /* number of values seen so far */
42   double count;
43   /* m in the description */
44   double multiplier;
45   double one_on_log_multiplier;
46   /* minimum value seen */
47   double min_seen;
48   /* maximum value seen */
49   double max_seen;
50   /* maximum representable value */
51   double max_possible;
52   /* number of buckets */
53   size_t num_buckets;
54   /* the buckets themselves */
55   uint32_t* buckets;
56 };
57 
58 /* determine a bucket index given a value - does no bounds checking */
bucket_for_unchecked(grpc_histogram * h,double x)59 static size_t bucket_for_unchecked(grpc_histogram* h, double x) {
60   return static_cast<size_t>(log(x) * h->one_on_log_multiplier);
61 }
62 
63 /* bounds checked version of the above */
bucket_for(grpc_histogram * h,double x)64 static size_t bucket_for(grpc_histogram* h, double x) {
65   size_t bucket = bucket_for_unchecked(h, GPR_CLAMP(x, 1.0, h->max_possible));
66   GPR_ASSERT(bucket < h->num_buckets);
67   return bucket;
68 }
69 
70 /* at what value does a bucket start? */
bucket_start(grpc_histogram * h,double x)71 static double bucket_start(grpc_histogram* h, double x) {
72   return pow(h->multiplier, x);
73 }
74 
grpc_histogram_create(double resolution,double max_bucket_start)75 grpc_histogram* grpc_histogram_create(double resolution,
76                                       double max_bucket_start) {
77   grpc_histogram* h =
78       static_cast<grpc_histogram*>(gpr_malloc(sizeof(grpc_histogram)));
79   GPR_ASSERT(resolution > 0.0);
80   GPR_ASSERT(max_bucket_start > resolution);
81   h->sum = 0.0;
82   h->sum_of_squares = 0.0;
83   h->multiplier = 1.0 + resolution;
84   h->one_on_log_multiplier = 1.0 / log(1.0 + resolution);
85   h->max_possible = max_bucket_start;
86   h->count = 0.0;
87   h->min_seen = max_bucket_start;
88   h->max_seen = 0.0;
89   h->num_buckets = bucket_for_unchecked(h, max_bucket_start) + 1;
90   GPR_ASSERT(h->num_buckets > 1);
91   GPR_ASSERT(h->num_buckets < 100000000);
92   h->buckets =
93       static_cast<uint32_t*>(gpr_zalloc(sizeof(uint32_t) * h->num_buckets));
94   return h;
95 }
96 
grpc_histogram_destroy(grpc_histogram * h)97 void grpc_histogram_destroy(grpc_histogram* h) {
98   gpr_free(h->buckets);
99   gpr_free(h);
100 }
101 
grpc_histogram_add(grpc_histogram * h,double x)102 void grpc_histogram_add(grpc_histogram* h, double x) {
103   h->sum += x;
104   h->sum_of_squares += x * x;
105   h->count++;
106   if (x < h->min_seen) {
107     h->min_seen = x;
108   }
109   if (x > h->max_seen) {
110     h->max_seen = x;
111   }
112   h->buckets[bucket_for(h, x)]++;
113 }
114 
grpc_histogram_merge(grpc_histogram * dst,const grpc_histogram * src)115 int grpc_histogram_merge(grpc_histogram* dst, const grpc_histogram* src) {
116   if ((dst->num_buckets != src->num_buckets) ||
117       (dst->multiplier != src->multiplier)) {
118     /* Fail because these histograms don't match */
119     return 0;
120   }
121   grpc_histogram_merge_contents(dst, src->buckets, src->num_buckets,
122                                 src->min_seen, src->max_seen, src->sum,
123                                 src->sum_of_squares, src->count);
124   return 1;
125 }
126 
grpc_histogram_merge_contents(grpc_histogram * dst,const uint32_t * data,size_t data_count,double min_seen,double max_seen,double sum,double sum_of_squares,double count)127 void grpc_histogram_merge_contents(grpc_histogram* dst, const uint32_t* data,
128                                    size_t data_count, double min_seen,
129                                    double max_seen, double sum,
130                                    double sum_of_squares, double count) {
131   size_t i;
132   GPR_ASSERT(dst->num_buckets == data_count);
133   dst->sum += sum;
134   dst->sum_of_squares += sum_of_squares;
135   dst->count += count;
136   if (min_seen < dst->min_seen) {
137     dst->min_seen = min_seen;
138   }
139   if (max_seen > dst->max_seen) {
140     dst->max_seen = max_seen;
141   }
142   for (i = 0; i < dst->num_buckets; i++) {
143     dst->buckets[i] += data[i];
144   }
145 }
146 
threshold_for_count_below(grpc_histogram * h,double count_below)147 static double threshold_for_count_below(grpc_histogram* h, double count_below) {
148   double count_so_far;
149   double lower_bound;
150   double upper_bound;
151   size_t lower_idx;
152   size_t upper_idx;
153 
154   if (h->count == 0) {
155     return 0.0;
156   }
157 
158   if (count_below <= 0) {
159     return h->min_seen;
160   }
161   if (count_below >= h->count) {
162     return h->max_seen;
163   }
164 
165   /* find the lowest bucket that gets us above count_below */
166   count_so_far = 0.0;
167   for (lower_idx = 0; lower_idx < h->num_buckets; lower_idx++) {
168     count_so_far += h->buckets[lower_idx];
169     if (count_so_far >= count_below) {
170       break;
171     }
172   }
173   if (count_so_far == count_below) {
174     /* this bucket hits the threshold exactly... we should be midway through
175        any run of zero values following the bucket */
176     for (upper_idx = lower_idx + 1; upper_idx < h->num_buckets; upper_idx++) {
177       if (h->buckets[upper_idx]) {
178         break;
179       }
180     }
181     return (bucket_start(h, static_cast<double>(lower_idx)) +
182             bucket_start(h, static_cast<double>(upper_idx))) /
183            2.0;
184   } else {
185     /* treat values as uniform throughout the bucket, and find where this value
186        should lie */
187     lower_bound = bucket_start(h, static_cast<double>(lower_idx));
188     upper_bound = bucket_start(h, static_cast<double>(lower_idx + 1));
189     return GPR_CLAMP(upper_bound - (upper_bound - lower_bound) *
190                                        (count_so_far - count_below) /
191                                        h->buckets[lower_idx],
192                      h->min_seen, h->max_seen);
193   }
194 }
195 
grpc_histogram_percentile(grpc_histogram * h,double percentile)196 double grpc_histogram_percentile(grpc_histogram* h, double percentile) {
197   return threshold_for_count_below(h, h->count * percentile / 100.0);
198 }
199 
grpc_histogram_mean(grpc_histogram * h)200 double grpc_histogram_mean(grpc_histogram* h) {
201   GPR_ASSERT(h->count != 0);
202   return h->sum / h->count;
203 }
204 
grpc_histogram_stddev(grpc_histogram * h)205 double grpc_histogram_stddev(grpc_histogram* h) {
206   return sqrt(grpc_histogram_variance(h));
207 }
208 
grpc_histogram_variance(grpc_histogram * h)209 double grpc_histogram_variance(grpc_histogram* h) {
210   if (h->count == 0) return 0.0;
211   return (h->sum_of_squares * h->count - h->sum * h->sum) /
212          (h->count * h->count);
213 }
214 
grpc_histogram_maximum(grpc_histogram * h)215 double grpc_histogram_maximum(grpc_histogram* h) { return h->max_seen; }
216 
grpc_histogram_minimum(grpc_histogram * h)217 double grpc_histogram_minimum(grpc_histogram* h) { return h->min_seen; }
218 
grpc_histogram_count(grpc_histogram * h)219 double grpc_histogram_count(grpc_histogram* h) { return h->count; }
220 
grpc_histogram_sum(grpc_histogram * h)221 double grpc_histogram_sum(grpc_histogram* h) { return h->sum; }
222 
grpc_histogram_sum_of_squares(grpc_histogram * h)223 double grpc_histogram_sum_of_squares(grpc_histogram* h) {
224   return h->sum_of_squares;
225 }
226 
grpc_histogram_get_contents(grpc_histogram * h,size_t * size)227 const uint32_t* grpc_histogram_get_contents(grpc_histogram* h, size_t* size) {
228   *size = h->num_buckets;
229   return h->buckets;
230 }
231