1 /*
2  * Copyright (C) 2013 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 #ifndef ART_LIBARTBASE_BASE_HISTOGRAM_H_
17 #define ART_LIBARTBASE_BASE_HISTOGRAM_H_
18 
19 #include <string>
20 #include <vector>
21 
22 #include <android-base/macros.h>
23 
24 namespace art {
25 
26 // Creates a data histogram  for a better understanding of statistical data.
27 // Histogram analysis goes beyond simple mean and standard deviation to provide
28 // percentiles values, describing where the $% of the input data lies.
29 // Designed to be simple and used with timing logger in art.
30 
31 template <class Value> class Histogram {
32   const double kAdjust;
33   const size_t kInitialBucketCount;
34 
35  public:
36   class CumulativeData {
37     friend class Histogram<Value>;
38     std::vector<uint64_t> freq_;
39     std::vector<double> perc_;
40   };
41 
42   // Used by the cumulative timing logger to search the histogram set using for an existing split
43   // with the same name using CumulativeLogger::HistogramComparator.
44   explicit Histogram(const char* name);
45   // This is the expected constructor when creating new Histograms.
46   Histogram(const char* name, Value initial_bucket_width, size_t max_buckets = 100);
47   void AddValue(Value);
48   void AdjustAndAddValue(Value);  // Add a value after dividing it by kAdjust.
49   // Builds the cumulative distribution function from the frequency data.
50   // Accumulative summation of frequencies.
51   // cumulative_freq[i] = sum(frequency[j] : 0 < j < i )
52   // Accumulative summation of percentiles; which is the frequency / SampleSize
53   // cumulative_perc[i] = sum(frequency[j] / SampleSize : 0 < j < i )
54   void CreateHistogram(CumulativeData* data) const;
55   // Reset the cumulative values, next time CreateHistogram is called it will recreate the cache.
56   void Reset();
57   double Mean() const;
58   double Variance() const;
59   double Percentile(double per, const CumulativeData& data) const;
60   void PrintConfidenceIntervals(std::ostream& os, double interval,
61                                 const CumulativeData& data) const;
62   void PrintMemoryUse(std::ostream& os) const;
63   void PrintBins(std::ostream& os, const CumulativeData& data) const;
64   void DumpBins(std::ostream& os) const;
65   Value GetRange(size_t bucket_idx) const;
66   size_t GetBucketCount() const;
67 
SampleSize()68   uint64_t SampleSize() const {
69     return sample_size_;
70   }
71 
Sum()72   Value Sum() const {
73     return sum_;
74   }
75 
AdjustedSum()76   Value AdjustedSum() const {
77     return sum_ * kAdjust;
78   }
79 
Min()80   Value Min() const {
81     return min_value_added_;
82   }
83 
Max()84   Value Max() const {
85     return max_value_added_;
86   }
87 
BucketWidth()88   Value BucketWidth() const {
89     return bucket_width_;
90   }
91 
Name()92   const std::string& Name() const {
93     return name_;
94   }
95 
96  private:
97   void Initialize();
98   size_t FindBucket(Value val) const;
99   void BucketiseValue(Value val);
100   // Add more buckets to the histogram to fill in a new value that exceeded
101   // the max_read_value_.
102   void GrowBuckets(Value val);
103   std::string name_;
104   // Maximum number of buckets.
105   const size_t max_buckets_;
106   // Number of samples placed in histogram.
107   size_t sample_size_;
108   // Width of the bucket range. The lower the value is the more accurate
109   // histogram percentiles are. Grows adaptively when we hit max buckets.
110   Value bucket_width_;
111   // How many occurrences of values fall within a bucket at index i where i covers the range
112   // starting at  min_ + i * bucket_width_ with size bucket_size_.
113   std::vector<uint32_t> frequency_;
114   // Summation of all the elements inputed by the user.
115   Value sum_;
116   // Minimum value that can fit in the histogram. Fixed to zero for now.
117   Value min_;
118   // Maximum value that can fit in the histogram, grows adaptively.
119   Value max_;
120   // Summation of the values entered. Used to calculate variance.
121   Value sum_of_squares_;
122   // Maximum value entered in the histogram.
123   Value min_value_added_;
124   // Minimum value entered in the histogram.
125   Value max_value_added_;
126 
127   DISALLOW_COPY_AND_ASSIGN(Histogram);
128 };
129 }  // namespace art
130 
131 #endif  // ART_LIBARTBASE_BASE_HISTOGRAM_H_
132