122 lines
3.8 KiB
C++
122 lines
3.8 KiB
C++
/*
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* Copyright (c) 2001, 2020, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#ifndef SHARE_GC_G1_G1MMUTRACKER_HPP
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#define SHARE_GC_G1_G1MMUTRACKER_HPP
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#include "gc/shared/gcId.hpp"
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#include "memory/allocation.hpp"
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#include "utilities/debug.hpp"
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class G1MMUTrackerElem {
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private:
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double _start_time;
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double _end_time;
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public:
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inline double start_time() { return _start_time; }
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inline double end_time() { return _end_time; }
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inline double duration() { return _end_time - _start_time; }
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G1MMUTrackerElem() {
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_start_time = 0.0;
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_end_time = 0.0;
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}
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G1MMUTrackerElem(double start_time, double end_time) {
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_start_time = start_time;
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_end_time = end_time;
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}
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};
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// Two major user controls over G1 behavior are setting a pause
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// time goal (MaxGCPauseMillis), over a time slice (GCPauseIntervalMillis).
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// This defines the Minimum Mutator Utilisation (MMU) goal.
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//
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// * Definitions *
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// Mutator Utilisation:
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// - for a given time slice duration "ts",
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// - mutator utilisation is the following fraction:
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// non_gc_time / ts
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//
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// Minimum Mutator Utilisation (MMU):
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// - the worst mutator utilisation across all time slices.
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//
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// The G1MMUTracker uses a fixed-size queue to keep track of all
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// recent pause times. The pause time data is used to avoid
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// breaking the MMU.
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//
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// ***** ALL TIMES ARE IN SECS!!!!!!! *****
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class G1MMUTracker: public CHeapObj<mtGC> {
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private:
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enum PrivateConstants {
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QueueLength = 64
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};
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double _time_slice;
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double _max_gc_time; // this is per time slice
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// The array keeps track of all the pauses that fall within a time
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// slice (the last time slice during which pauses took place).
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// The data structure implemented is a circular queue.
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// Head "points" to the most recent addition, tail to the oldest one.
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// The array is of fixed size and I don't think we'll need more than
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// two or three entries with the current behavior of G1 pauses.
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// If the array is full, an easy fix is to look for the pauses with
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// the shortest gap between them and consolidate them.
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// For now, we have taken the expedient alternative of forgetting
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// the oldest entry, thus potentially violating MMU specs for
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// some time thereafter.
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G1MMUTrackerElem _array[QueueLength];
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int _head_index;
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int _tail_index;
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int _no_entries;
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inline int trim_index(int index) {
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return (index + QueueLength) % QueueLength;
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}
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void remove_expired_entries(double current_time);
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double calculate_gc_time(double current_time);
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public:
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G1MMUTracker(double time_slice, double max_gc_time);
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void add_pause(double start, double end);
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double when_sec(double current_time, double pause_time);
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double max_gc_time() const {
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return _max_gc_time;
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}
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double when_max_gc_sec(double current_time) {
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return when_sec(current_time, max_gc_time());
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}
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};
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#endif // SHARE_GC_G1_G1MMUTRACKER_HPP
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