Mercurial > hg > truffle
comparison src/share/vm/gc_implementation/shared/coTracker.hpp @ 362:f8199438385b
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author | apetrusenko |
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date | Wed, 17 Sep 2008 16:49:18 +0400 |
parents | 37f87013dfd8 |
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1 /* | |
2 * Copyright 2001-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
20 * CA 95054 USA or visit www.sun.com if you need additional information or | |
21 * have any questions. | |
22 * | |
23 */ | |
24 | |
25 // COTracker keeps track of the concurrent overhead of a GC thread. | |
26 | |
27 // A thread that needs to be tracked must, itself, start up its | |
28 // tracker with the start() method and then call the update() method | |
29 // at regular intervals. What the tracker does is to calculate the | |
30 // concurrent overhead of a process at a given update period. The | |
31 // tracker starts and when is detects that it has exceeded the given | |
32 // period, it calculates the duration of the period in wall-clock time | |
33 // and the duration of the period in vtime (i.e. how much time the | |
34 // concurrent processes really took up during this period). The ratio | |
35 // of the latter over the former is the concurrent overhead of that | |
36 // process for that period over a single CPU. This overhead is stored | |
37 // on the tracker, "timestamped" with the wall-clock time of the end | |
38 // of the period. When the concurrent overhead of this process needs | |
39 // to be queried, this last "reading" provides a good approximation | |
40 // (we assume that the concurrent overhead of a particular thread | |
41 // stays largely constant over time). The timestamp is necessary to | |
42 // detect when the process has stopped working and the recorded | |
43 // reading hasn't been updated for some time. | |
44 | |
45 // Each concurrent GC thread is considered to be part of a "group" | |
46 // (i.e. any available concurrent marking threads are part of the | |
47 // "concurrent marking thread group"). A COTracker is associated with | |
48 // a single group at construction-time. It's up to each collector to | |
49 // decide how groups will be mapped to such an id (ids should start | |
50 // from 0 and be consecutive; there's a hardcoded max group num | |
51 // defined on the GCOverheadTracker class). The notion of a group has | |
52 // been introduced to be able to identify how much overhead was | |
53 // imposed by each group, instead of getting a single value that | |
54 // covers all concurrent overhead. | |
55 | |
56 class COTracker { | |
57 private: | |
58 // It indicates whether this tracker is enabled or not. When the | |
59 // tracker is disabled, then it returns 0.0 as the latest concurrent | |
60 // overhead and several methods (reset, start, and update) are not | |
61 // supposed to be called on it. This enabling / disabling facility | |
62 // is really provided to make a bit more explicit in the code when a | |
63 // particulary tracker of a processes that doesn't run all the time | |
64 // (e.g. concurrent marking) is supposed to be used and not it's not. | |
65 bool _enabled; | |
66 | |
67 // The ID of the group associated with this tracker. | |
68 int _group; | |
69 | |
70 // The update period of the tracker. A new value for the concurrent | |
71 // overhead of the associated process will be made at intervals no | |
72 // smaller than this. | |
73 double _update_period_sec; | |
74 | |
75 // The start times (both wall-block time and vtime) of the current | |
76 // interval. | |
77 double _period_start_time_sec; | |
78 double _period_start_vtime_sec; | |
79 | |
80 // Number seq of the concurrent overhead readings within a period | |
81 NumberSeq _conc_overhead_seq; | |
82 | |
83 // The latest reading of the concurrent overhead (over a single CPU) | |
84 // imposed by the associated concurrent thread, made available at | |
85 // the indicated wall-clock time. | |
86 double _conc_overhead; | |
87 double _time_stamp_sec; | |
88 | |
89 // The number of CPUs that the host machine has (for convenience | |
90 // really, as we'd have to keep translating it into a double) | |
91 static double _cpu_number; | |
92 | |
93 // Fields that keep a list of all trackers created. This is useful, | |
94 // since it allows us to sum up the concurrent overhead without | |
95 // having to write code for a specific collector to broadcast a | |
96 // request to all its concurrent processes. | |
97 COTracker* _next; | |
98 static COTracker* _head; | |
99 | |
100 // It indicates that a new period is starting by updating the | |
101 // _period_start_time_sec and _period_start_vtime_sec fields. | |
102 void resetPeriod(double now_sec, double vnow_sec); | |
103 // It updates the latest concurrent overhead reading, taken at a | |
104 // given wall-clock time. | |
105 void setConcOverhead(double time_stamp_sec, double conc_overhead); | |
106 | |
107 // It determines whether the time stamp of the latest concurrent | |
108 // overhead reading is out of date or not. | |
109 bool outOfDate(double now_sec) { | |
110 // The latest reading is considered out of date, if it was taken | |
111 // 1.2x the update period. | |
112 return (now_sec - _time_stamp_sec) > 1.2 * _update_period_sec; | |
113 } | |
114 | |
115 public: | |
116 // The constructor which associates the tracker with a group ID. | |
117 COTracker(int group); | |
118 | |
119 // Methods to enable / disable the tracker and query whether it is enabled. | |
120 void enable() { _enabled = true; } | |
121 void disable() { _enabled = false; } | |
122 bool enabled() { return _enabled; } | |
123 | |
124 // It resets the tracker and sets concurrent overhead reading to be | |
125 // the given parameter and the associated time stamp to be now. | |
126 void reset(double starting_conc_overhead = 0.0); | |
127 // The tracker starts tracking. IT should only be called from the | |
128 // concurrent thread that is tracked by this tracker. | |
129 void start(); | |
130 // It updates the tracker and, if the current period is longer than | |
131 // the update period, the concurrent overhead reading will be | |
132 // updated. force_end being true indicates that it's the last call | |
133 // to update() by this process before the tracker is disabled (the | |
134 // tracker can be re-enabled later if necessary). It should only be | |
135 // called from the concurrent thread that is tracked by this tracker | |
136 // and while the thread has joined the STS. | |
137 void update(bool force_end = false); | |
138 // It adjusts the contents of the tracker to take into account a STW | |
139 // pause. | |
140 void updateForSTW(double start_sec, double end_sec); | |
141 | |
142 // It returns the last concurrent overhead reading over a single | |
143 // CPU. If the reading is out of date, or the tracker is disabled, | |
144 // it returns 0.0. | |
145 double concCPUOverhead(double now_sec) { | |
146 if (!_enabled || outOfDate(now_sec)) | |
147 return 0.0; | |
148 else | |
149 return _conc_overhead; | |
150 } | |
151 | |
152 // It returns the last concurrent overhead reading over all CPUs | |
153 // that the host machine has. If the reading is out of date, or the | |
154 // tracker is disabled, it returns 0.0. | |
155 double concOverhead(double now_sec) { | |
156 return concCPUOverhead(now_sec) / _cpu_number; | |
157 } | |
158 | |
159 double predConcOverhead(); | |
160 | |
161 void resetPred(); | |
162 | |
163 // statics | |
164 | |
165 // It notifies all trackers about a STW pause. | |
166 static void updateAllForSTW(double start_sec, double end_sec); | |
167 | |
168 // It returns the sum of the concurrent overhead readings of all | |
169 // available (and enabled) trackers for the given time stamp. The | |
170 // overhead is over all the CPUs of the host machine. | |
171 | |
172 static double totalConcOverhead(double now_sec); | |
173 // Like the previous method, but it also sums up the overheads per | |
174 // group number. The length of the co_per_group array must be at | |
175 // least as large group_num | |
176 static double totalConcOverhead(double now_sec, | |
177 size_t group_num, | |
178 double* co_per_group); | |
179 | |
180 static double totalPredConcOverhead(); | |
181 }; |