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view src/share/vm/gc_implementation/shared/coTracker.hpp @ 771:a77eddcd510c jdk7-b60
6843041: Remove duplicate README files in repositories (make/README)
Reviewed-by: robilad
author | ohair |
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date | Tue, 19 May 2009 17:40:10 -0700 |
parents | 37f87013dfd8 |
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/* * Copyright 2001-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, * CA 95054 USA or visit www.sun.com if you need additional information or * have any questions. * */ // COTracker keeps track of the concurrent overhead of a GC thread. // A thread that needs to be tracked must, itself, start up its // tracker with the start() method and then call the update() method // at regular intervals. What the tracker does is to calculate the // concurrent overhead of a process at a given update period. The // tracker starts and when is detects that it has exceeded the given // period, it calculates the duration of the period in wall-clock time // and the duration of the period in vtime (i.e. how much time the // concurrent processes really took up during this period). The ratio // of the latter over the former is the concurrent overhead of that // process for that period over a single CPU. This overhead is stored // on the tracker, "timestamped" with the wall-clock time of the end // of the period. When the concurrent overhead of this process needs // to be queried, this last "reading" provides a good approximation // (we assume that the concurrent overhead of a particular thread // stays largely constant over time). The timestamp is necessary to // detect when the process has stopped working and the recorded // reading hasn't been updated for some time. // Each concurrent GC thread is considered to be part of a "group" // (i.e. any available concurrent marking threads are part of the // "concurrent marking thread group"). A COTracker is associated with // a single group at construction-time. It's up to each collector to // decide how groups will be mapped to such an id (ids should start // from 0 and be consecutive; there's a hardcoded max group num // defined on the GCOverheadTracker class). The notion of a group has // been introduced to be able to identify how much overhead was // imposed by each group, instead of getting a single value that // covers all concurrent overhead. class COTracker { private: // It indicates whether this tracker is enabled or not. When the // tracker is disabled, then it returns 0.0 as the latest concurrent // overhead and several methods (reset, start, and update) are not // supposed to be called on it. This enabling / disabling facility // is really provided to make a bit more explicit in the code when a // particulary tracker of a processes that doesn't run all the time // (e.g. concurrent marking) is supposed to be used and not it's not. bool _enabled; // The ID of the group associated with this tracker. int _group; // The update period of the tracker. A new value for the concurrent // overhead of the associated process will be made at intervals no // smaller than this. double _update_period_sec; // The start times (both wall-block time and vtime) of the current // interval. double _period_start_time_sec; double _period_start_vtime_sec; // Number seq of the concurrent overhead readings within a period NumberSeq _conc_overhead_seq; // The latest reading of the concurrent overhead (over a single CPU) // imposed by the associated concurrent thread, made available at // the indicated wall-clock time. double _conc_overhead; double _time_stamp_sec; // The number of CPUs that the host machine has (for convenience // really, as we'd have to keep translating it into a double) static double _cpu_number; // Fields that keep a list of all trackers created. This is useful, // since it allows us to sum up the concurrent overhead without // having to write code for a specific collector to broadcast a // request to all its concurrent processes. COTracker* _next; static COTracker* _head; // It indicates that a new period is starting by updating the // _period_start_time_sec and _period_start_vtime_sec fields. void resetPeriod(double now_sec, double vnow_sec); // It updates the latest concurrent overhead reading, taken at a // given wall-clock time. void setConcOverhead(double time_stamp_sec, double conc_overhead); // It determines whether the time stamp of the latest concurrent // overhead reading is out of date or not. bool outOfDate(double now_sec) { // The latest reading is considered out of date, if it was taken // 1.2x the update period. return (now_sec - _time_stamp_sec) > 1.2 * _update_period_sec; } public: // The constructor which associates the tracker with a group ID. COTracker(int group); // Methods to enable / disable the tracker and query whether it is enabled. void enable() { _enabled = true; } void disable() { _enabled = false; } bool enabled() { return _enabled; } // It resets the tracker and sets concurrent overhead reading to be // the given parameter and the associated time stamp to be now. void reset(double starting_conc_overhead = 0.0); // The tracker starts tracking. IT should only be called from the // concurrent thread that is tracked by this tracker. void start(); // It updates the tracker and, if the current period is longer than // the update period, the concurrent overhead reading will be // updated. force_end being true indicates that it's the last call // to update() by this process before the tracker is disabled (the // tracker can be re-enabled later if necessary). It should only be // called from the concurrent thread that is tracked by this tracker // and while the thread has joined the STS. void update(bool force_end = false); // It adjusts the contents of the tracker to take into account a STW // pause. void updateForSTW(double start_sec, double end_sec); // It returns the last concurrent overhead reading over a single // CPU. If the reading is out of date, or the tracker is disabled, // it returns 0.0. double concCPUOverhead(double now_sec) { if (!_enabled || outOfDate(now_sec)) return 0.0; else return _conc_overhead; } // It returns the last concurrent overhead reading over all CPUs // that the host machine has. If the reading is out of date, or the // tracker is disabled, it returns 0.0. double concOverhead(double now_sec) { return concCPUOverhead(now_sec) / _cpu_number; } double predConcOverhead(); void resetPred(); // statics // It notifies all trackers about a STW pause. static void updateAllForSTW(double start_sec, double end_sec); // It returns the sum of the concurrent overhead readings of all // available (and enabled) trackers for the given time stamp. The // overhead is over all the CPUs of the host machine. static double totalConcOverhead(double now_sec); // Like the previous method, but it also sums up the overheads per // group number. The length of the co_per_group array must be at // least as large group_num static double totalConcOverhead(double now_sec, size_t group_num, double* co_per_group); static double totalPredConcOverhead(); };