g1MMUTracker.cpp revision 8413:92457dfb91bd 
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.
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
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23 */
24
25#include "precompiled.hpp"
26#include "gc/g1/g1MMUTracker.hpp"
27#include "runtime/mutexLocker.hpp"
28#include "utilities/ostream.hpp"
29
30#define _DISABLE_MMU                             0
31
32// can't rely on comparing doubles with tolerating a small margin for error
33#define SMALL_MARGIN 0.0000001
34#define is_double_leq_0(_value) ( (_value) < SMALL_MARGIN )
35#define is_double_leq(_val1, _val2) is_double_leq_0((_val1) - (_val2))
36#define is_double_geq(_val1, _val2) is_double_leq_0((_val2) - (_val1))
37
38/***** ALL TIMES ARE IN SECS!!!!!!! *****/
39
40G1MMUTracker::G1MMUTracker(double time_slice, double max_gc_time) :
41  _time_slice(time_slice),
42  _max_gc_time(max_gc_time) { }
43
44G1MMUTrackerQueue::G1MMUTrackerQueue(double time_slice, double max_gc_time) :
45  G1MMUTracker(time_slice, max_gc_time),
46  _head_index(0),
47  _tail_index(trim_index(_head_index+1)),
48  _no_entries(0) { }
49
50void G1MMUTrackerQueue::remove_expired_entries(double current_time) {
51  double limit = current_time - _time_slice;
52  while (_no_entries > 0) {
53    if (is_double_geq(limit, _array[_tail_index].end_time())) {
54      _tail_index = trim_index(_tail_index + 1);
55      --_no_entries;
56    } else
57      return;
58  }
59  guarantee(_no_entries == 0, "should have no entries in the array");
60}
61
62double G1MMUTrackerQueue::calculate_gc_time(double current_time) {
63  double gc_time = 0.0;
64  double limit = current_time - _time_slice;
65  for (int i = 0; i < _no_entries; ++i) {
66    int index = trim_index(_tail_index + i);
67    G1MMUTrackerQueueElem *elem = &_array[index];
68    if (elem->end_time() > limit) {
69      if (elem->start_time() > limit)
70        gc_time += elem->duration();
71      else
72        gc_time += elem->end_time() - limit;
73    }
74  }
75  return gc_time;
76}
77
78void G1MMUTrackerQueue::add_pause(double start, double end, bool gc_thread) {
79  double duration = end - start;
80
81  remove_expired_entries(end);
82  if (_no_entries == QueueLength) {
83    // OK, we've filled up the queue. There are a few ways
84    // of dealing with this "gracefully"
85    //   increase the array size (:-)
86    //   remove the oldest entry (this might allow more GC time for
87    //     the time slice than what's allowed) - this is what we
88    //     currently do
89    //   consolidate the two entries with the minimum gap between them
90    //     (this might allow less GC time than what's allowed)
91
92    // In the case where ScavengeALot is true, such overflow is not
93    // uncommon; in such cases, we can, without much loss of precision
94    // or performance (we are GC'ing most of the time anyway!),
95    // simply overwrite the oldest entry in the tracker.
96
97    _head_index = trim_index(_head_index + 1);
98    assert(_head_index == _tail_index, "Because we have a full circular buffer");
99    _tail_index = trim_index(_tail_index + 1);
100  } else {
101    _head_index = trim_index(_head_index + 1);
102    ++_no_entries;
103  }
104  _array[_head_index] = G1MMUTrackerQueueElem(start, end);
105}
106
107// basically the _internal call does not remove expired entries
108// this is for trying things out in the future and a couple
109// of other places (debugging)
110
111double G1MMUTrackerQueue::when_sec(double current_time, double pause_time) {
112  if (_DISABLE_MMU)
113    return 0.0;
114
115  MutexLockerEx x(MMUTracker_lock, Mutex::_no_safepoint_check_flag);
116  remove_expired_entries(current_time);
117
118  return when_internal(current_time, pause_time);
119}
120
121double G1MMUTrackerQueue::when_internal(double current_time,
122                                        double pause_time) {
123  // if the pause is over the maximum, just assume that it's the maximum
124  double adjusted_pause_time =
125    (pause_time > max_gc_time()) ? max_gc_time() : pause_time;
126  double earliest_end = current_time + adjusted_pause_time;
127  double limit = earliest_end - _time_slice;
128  double gc_time = calculate_gc_time(earliest_end);
129  double diff = gc_time + adjusted_pause_time - max_gc_time();
130  if (is_double_leq_0(diff))
131    return 0.0;
132
133  int index = _tail_index;
134  while ( 1 ) {
135    G1MMUTrackerQueueElem *elem = &_array[index];
136    if (elem->end_time() > limit) {
137      if (elem->start_time() > limit)
138        diff -= elem->duration();
139      else
140        diff -= elem->end_time() - limit;
141      if (is_double_leq_0(diff))
142        return  elem->end_time() + diff + _time_slice - adjusted_pause_time - current_time;
143    }
144    index = trim_index(index+1);
145    guarantee(index != trim_index(_head_index + 1), "should not go past head");
146  }
147}
148