1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/gc_implementation/shared/coTracker.hpp Thu Jun 05 15:57:56 2008 -0700
1.3 @@ -0,0 +1,181 @@
1.4 +/*
1.5 + * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
1.23 + * CA 95054 USA or visit www.sun.com if you need additional information or
1.24 + * have any questions.
1.25 + *
1.26 + */
1.27 +
1.28 +// COTracker keeps track of the concurrent overhead of a GC thread.
1.29 +
1.30 +// A thread that needs to be tracked must, itself, start up its
1.31 +// tracker with the start() method and then call the update() method
1.32 +// at regular intervals. What the tracker does is to calculate the
1.33 +// concurrent overhead of a process at a given update period. The
1.34 +// tracker starts and when is detects that it has exceeded the given
1.35 +// period, it calculates the duration of the period in wall-clock time
1.36 +// and the duration of the period in vtime (i.e. how much time the
1.37 +// concurrent processes really took up during this period). The ratio
1.38 +// of the latter over the former is the concurrent overhead of that
1.39 +// process for that period over a single CPU. This overhead is stored
1.40 +// on the tracker, "timestamped" with the wall-clock time of the end
1.41 +// of the period. When the concurrent overhead of this process needs
1.42 +// to be queried, this last "reading" provides a good approximation
1.43 +// (we assume that the concurrent overhead of a particular thread
1.44 +// stays largely constant over time). The timestamp is necessary to
1.45 +// detect when the process has stopped working and the recorded
1.46 +// reading hasn't been updated for some time.
1.47 +
1.48 +// Each concurrent GC thread is considered to be part of a "group"
1.49 +// (i.e. any available concurrent marking threads are part of the
1.50 +// "concurrent marking thread group"). A COTracker is associated with
1.51 +// a single group at construction-time. It's up to each collector to
1.52 +// decide how groups will be mapped to such an id (ids should start
1.53 +// from 0 and be consecutive; there's a hardcoded max group num
1.54 +// defined on the GCOverheadTracker class). The notion of a group has
1.55 +// been introduced to be able to identify how much overhead was
1.56 +// imposed by each group, instead of getting a single value that
1.57 +// covers all concurrent overhead.
1.58 +
1.59 +class COTracker {
1.60 +private:
1.61 + // It indicates whether this tracker is enabled or not. When the
1.62 + // tracker is disabled, then it returns 0.0 as the latest concurrent
1.63 + // overhead and several methods (reset, start, and update) are not
1.64 + // supposed to be called on it. This enabling / disabling facility
1.65 + // is really provided to make a bit more explicit in the code when a
1.66 + // particulary tracker of a processes that doesn't run all the time
1.67 + // (e.g. concurrent marking) is supposed to be used and not it's not.
1.68 + bool _enabled;
1.69 +
1.70 + // The ID of the group associated with this tracker.
1.71 + int _group;
1.72 +
1.73 + // The update period of the tracker. A new value for the concurrent
1.74 + // overhead of the associated process will be made at intervals no
1.75 + // smaller than this.
1.76 + double _update_period_sec;
1.77 +
1.78 + // The start times (both wall-block time and vtime) of the current
1.79 + // interval.
1.80 + double _period_start_time_sec;
1.81 + double _period_start_vtime_sec;
1.82 +
1.83 + // Number seq of the concurrent overhead readings within a period
1.84 + NumberSeq _conc_overhead_seq;
1.85 +
1.86 + // The latest reading of the concurrent overhead (over a single CPU)
1.87 + // imposed by the associated concurrent thread, made available at
1.88 + // the indicated wall-clock time.
1.89 + double _conc_overhead;
1.90 + double _time_stamp_sec;
1.91 +
1.92 + // The number of CPUs that the host machine has (for convenience
1.93 + // really, as we'd have to keep translating it into a double)
1.94 + static double _cpu_number;
1.95 +
1.96 + // Fields that keep a list of all trackers created. This is useful,
1.97 + // since it allows us to sum up the concurrent overhead without
1.98 + // having to write code for a specific collector to broadcast a
1.99 + // request to all its concurrent processes.
1.100 + COTracker* _next;
1.101 + static COTracker* _head;
1.102 +
1.103 + // It indicates that a new period is starting by updating the
1.104 + // _period_start_time_sec and _period_start_vtime_sec fields.
1.105 + void resetPeriod(double now_sec, double vnow_sec);
1.106 + // It updates the latest concurrent overhead reading, taken at a
1.107 + // given wall-clock time.
1.108 + void setConcOverhead(double time_stamp_sec, double conc_overhead);
1.109 +
1.110 + // It determines whether the time stamp of the latest concurrent
1.111 + // overhead reading is out of date or not.
1.112 + bool outOfDate(double now_sec) {
1.113 + // The latest reading is considered out of date, if it was taken
1.114 + // 1.2x the update period.
1.115 + return (now_sec - _time_stamp_sec) > 1.2 * _update_period_sec;
1.116 + }
1.117 +
1.118 +public:
1.119 + // The constructor which associates the tracker with a group ID.
1.120 + COTracker(int group);
1.121 +
1.122 + // Methods to enable / disable the tracker and query whether it is enabled.
1.123 + void enable() { _enabled = true; }
1.124 + void disable() { _enabled = false; }
1.125 + bool enabled() { return _enabled; }
1.126 +
1.127 + // It resets the tracker and sets concurrent overhead reading to be
1.128 + // the given parameter and the associated time stamp to be now.
1.129 + void reset(double starting_conc_overhead = 0.0);
1.130 + // The tracker starts tracking. IT should only be called from the
1.131 + // concurrent thread that is tracked by this tracker.
1.132 + void start();
1.133 + // It updates the tracker and, if the current period is longer than
1.134 + // the update period, the concurrent overhead reading will be
1.135 + // updated. force_end being true indicates that it's the last call
1.136 + // to update() by this process before the tracker is disabled (the
1.137 + // tracker can be re-enabled later if necessary). It should only be
1.138 + // called from the concurrent thread that is tracked by this tracker
1.139 + // and while the thread has joined the STS.
1.140 + void update(bool force_end = false);
1.141 + // It adjusts the contents of the tracker to take into account a STW
1.142 + // pause.
1.143 + void updateForSTW(double start_sec, double end_sec);
1.144 +
1.145 + // It returns the last concurrent overhead reading over a single
1.146 + // CPU. If the reading is out of date, or the tracker is disabled,
1.147 + // it returns 0.0.
1.148 + double concCPUOverhead(double now_sec) {
1.149 + if (!_enabled || outOfDate(now_sec))
1.150 + return 0.0;
1.151 + else
1.152 + return _conc_overhead;
1.153 + }
1.154 +
1.155 + // It returns the last concurrent overhead reading over all CPUs
1.156 + // that the host machine has. If the reading is out of date, or the
1.157 + // tracker is disabled, it returns 0.0.
1.158 + double concOverhead(double now_sec) {
1.159 + return concCPUOverhead(now_sec) / _cpu_number;
1.160 + }
1.161 +
1.162 + double predConcOverhead();
1.163 +
1.164 + void resetPred();
1.165 +
1.166 + // statics
1.167 +
1.168 + // It notifies all trackers about a STW pause.
1.169 + static void updateAllForSTW(double start_sec, double end_sec);
1.170 +
1.171 + // It returns the sum of the concurrent overhead readings of all
1.172 + // available (and enabled) trackers for the given time stamp. The
1.173 + // overhead is over all the CPUs of the host machine.
1.174 +
1.175 + static double totalConcOverhead(double now_sec);
1.176 + // Like the previous method, but it also sums up the overheads per
1.177 + // group number. The length of the co_per_group array must be at
1.178 + // least as large group_num
1.179 + static double totalConcOverhead(double now_sec,
1.180 + size_t group_num,
1.181 + double* co_per_group);
1.182 +
1.183 + static double totalPredConcOverhead();
1.184 +};
