Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * 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

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  */

 // 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();

 };