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