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. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 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 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 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. 31 class 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