1 /*
2 * Copyright (c) 2001, 2015, 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
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.
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23 */
24
25 #ifndef SHARE_VM_GC_G1_G1MMUTRACKER_HPP
26 #define SHARE_VM_GC_G1_G1MMUTRACKER_HPP
27
28 #include "gc/shared/gcId.hpp"
29 #include "memory/allocation.hpp"
30 #include "utilities/debug.hpp"
31
32 // Two major user controls over G1 behavior are setting a pause time goal (MaxGCPauseMillis),
33 // over a time slice (GCPauseIntervalMillis). This defines the Minimum Mutator
34 // Utilisation (MMU) goal.
35 //
36 // * Definitions *
37 // Mutator Utilisation:
38 // - for a given time slice duration "ts",
39 // - mutator utilisation is the following fraction:
40 // non_gc_time / ts
41 //
42 // Minimum Mutator Utilisation (MMU):
43 // - the worst mutator utilisation across all time slices.
44 //
45 // G1MMUTracker keeps track of the GC work and decides when it is OK to do GC work
46 // and for how long so that the MMU invariants are maintained.
47 //
48 // ***** ALL TIMES ARE IN SECS!!!!!!! *****
49 // this is the "interface"
50 class G1MMUTracker: public CHeapObj<mtGC> {
51 protected:
52 double _time_slice;
53 double _max_gc_time; // this is per time slice
54
55 public:
56 G1MMUTracker(double time_slice, double max_gc_time);
57
58 virtual void add_pause(double start, double end) = 0;
59 virtual double when_sec(double current_time, double pause_time) = 0;
60
61 double max_gc_time() const {
62 return _max_gc_time;
63 }
64
65 inline bool now_max_gc(double current_time) {
66 return when_sec(current_time, max_gc_time()) < 0.00001;
67 }
68
69 inline double when_max_gc_sec(double current_time) {
70 return when_sec(current_time, max_gc_time());
71 }
72
73 inline jlong when_max_gc_ms(double current_time) {
74 double when = when_max_gc_sec(current_time);
75 return (jlong) (when * 1000.0);
76 }
77
78 inline jlong when_ms(double current_time, double pause_time) {
79 double when = when_sec(current_time, pause_time);
80 return (jlong) (when * 1000.0);
81 }
82 };
83
84 class G1MMUTrackerQueueElem {
85 private:
86 double _start_time;
87 double _end_time;
88
89 public:
90 inline double start_time() { return _start_time; }
91 inline double end_time() { return _end_time; }
92 inline double duration() { return _end_time - _start_time; }
93
94 G1MMUTrackerQueueElem() {
95 _start_time = 0.0;
96 _end_time = 0.0;
97 }
98
99 G1MMUTrackerQueueElem(double start_time, double end_time) {
100 _start_time = start_time;
101 _end_time = end_time;
102 }
103 };
104
105 // this is an implementation of the MMUTracker using a (fixed-size) queue
106 // that keeps track of all the recent pause times
107 class G1MMUTrackerQueue: public G1MMUTracker {
108 private:
109 enum PrivateConstants {
110 QueueLength = 64
111 };
112
113 // The array keeps track of all the pauses that fall within a time
114 // slice (the last time slice during which pauses took place).
115 // The data structure implemented is a circular queue.
116 // Head "points" to the most recent addition, tail to the oldest one.
117 // The array is of fixed size and I don't think we'll need more than
118 // two or three entries with the current behavior of G1 pauses.
119 // If the array is full, an easy fix is to look for the pauses with
120 // the shortest gap between them and consolidate them.
121 // For now, we have taken the expedient alternative of forgetting
122 // the oldest entry in the event that +G1UseFixedWindowMMUTracker, thus
123 // potentially violating MMU specs for some time thereafter.
124
125 G1MMUTrackerQueueElem _array[QueueLength];
126 int _head_index;
127 int _tail_index;
128 int _no_entries;
129
130 inline int trim_index(int index) {
131 return (index + QueueLength) % QueueLength;
132 }
133
134 void remove_expired_entries(double current_time);
135 double calculate_gc_time(double current_time);
136
137 public:
138 G1MMUTrackerQueue(double time_slice, double max_gc_time);
139
140 virtual void add_pause(double start, double end);
141
142 virtual double when_sec(double current_time, double pause_time);
143 };
144
145 #endif // SHARE_VM_GC_G1_G1MMUTRACKER_HPP