1/*
2 * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
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24
25#ifndef SHARE_VM_GC_G1_G1PREDICTIONS_HPP
26#define SHARE_VM_GC_G1_G1PREDICTIONS_HPP
27
28#include "utilities/numberSeq.hpp"
29
30// Utility class containing various helper methods for prediction.
31class G1Predictions VALUE_OBJ_CLASS_SPEC {
32 private:
33  double _sigma;
34
35  // This function is used to estimate the stddev of sample sets. There is some
36  // special consideration of small sample sets: the actual stddev for them is
37  // not very useful, so we calculate some value based on the sample average.
38  // Five or more samples yields zero (at that point we use the stddev); fewer
39  // scale the sample set average linearly from two times the average to 0.5 times
40  // it.
41  double stddev_estimate(TruncatedSeq const* seq) const {
42    double estimate = seq->dsd();
43    int const samples = seq->num();
44    if (samples < 5) {
45      estimate = MAX2(seq->davg() * (5 - samples) / 2.0, estimate);
46    }
47    return estimate;
48  }
49 public:
50  G1Predictions(double sigma) : _sigma(sigma) {
51    assert(sigma >= 0.0, "Confidence must be larger than or equal to zero");
52  }
53
54  // Confidence factor.
55  double sigma() const { return _sigma; }
56
57  double get_new_prediction(TruncatedSeq const* seq) const {
58    return seq->davg() + _sigma * stddev_estimate(seq);
59  }
60};
61
62#endif // SHARE_VM_GC_G1_G1PREDICTIONS_HPP
63