view src/share/vm/gc_implementation/g1/g1MMUTracker.cpp @ 2034:7e37af9d69ef

7011379: G1: overly long concurrent marking cycles Summary: This changeset introduces filtering of SATB buffers at the point when they are about to be enqueued. If this filtering clears enough entries on each buffer, the buffer can then be re-used and not enqueued. This cuts down the number of SATB buffers that need to be processed by the concurrent marking threads. Reviewed-by: johnc, ysr
author tonyp
date Wed, 19 Jan 2011 09:35:17 -0500
parents b9bc732be7c0
children 20213c8a3c40
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/*
 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 *
 */

#include "precompiled.hpp"
#include "gc_implementation/g1/g1MMUTracker.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/ostream.hpp"

#define _DISABLE_MMU                             0

// can't rely on comparing doubles with tolerating a small margin for error
#define SMALL_MARGIN 0.0000001
#define is_double_leq_0(_value) ( (_value) < SMALL_MARGIN )
#define is_double_leq(_val1, _val2) is_double_leq_0((_val1) - (_val2))
#define is_double_geq(_val1, _val2) is_double_leq_0((_val2) - (_val1))

/***** ALL TIMES ARE IN SECS!!!!!!! *****/

G1MMUTracker::G1MMUTracker(double time_slice, double max_gc_time) :
  _time_slice(time_slice),
  _max_gc_time(max_gc_time) { }

G1MMUTrackerQueue::G1MMUTrackerQueue(double time_slice, double max_gc_time) :
  G1MMUTracker(time_slice, max_gc_time),
  _head_index(0),
  _tail_index(trim_index(_head_index+1)),
  _no_entries(0) { }

void G1MMUTrackerQueue::remove_expired_entries(double current_time) {
  double limit = current_time - _time_slice;
  while (_no_entries > 0) {
    if (is_double_geq(limit, _array[_tail_index].end_time())) {
      _tail_index = trim_index(_tail_index + 1);
      --_no_entries;
    } else
      return;
  }
  guarantee(_no_entries == 0, "should have no entries in the array");
}

double G1MMUTrackerQueue::calculate_gc_time(double current_time) {
  double gc_time = 0.0;
  double limit = current_time - _time_slice;
  for (int i = 0; i < _no_entries; ++i) {
    int index = trim_index(_tail_index + i);
    G1MMUTrackerQueueElem *elem = &_array[index];
    if (elem->end_time() > limit) {
      if (elem->start_time() > limit)
        gc_time += elem->duration();
      else
        gc_time += elem->end_time() - limit;
    }
  }
  return gc_time;
}

void G1MMUTrackerQueue::add_pause(double start, double end, bool gc_thread) {
  double longest_allowed = longest_pause_internal(start);
  if (longest_allowed < 0.0)
    longest_allowed = 0.0;
  double duration = end - start;

  remove_expired_entries(end);
  if (_no_entries == QueueLength) {
    // OK, we've filled up the queue. There are a few ways
    // of dealing with this "gracefully"
    //   increase the array size (:-)
    //   remove the oldest entry (this might allow more GC time for
    //     the time slice than what's allowed) - this is what we
    //     currently do
    //   consolidate the two entries with the minimum gap between them
    //     (this might allow less GC time than what's allowed)

    // In the case where ScavengeALot is true, such overflow is not
    // uncommon; in such cases, we can, without much loss of precision
    // or performance (we are GC'ing most of the time anyway!),
    // simply overwrite the oldest entry in the tracker.

    if (G1PolicyVerbose > 1) {
      warning("MMU Tracker Queue overflow. Replacing earliest entry.");
    }

    _head_index = trim_index(_head_index + 1);
    assert(_head_index == _tail_index, "Because we have a full circular buffer");
    _tail_index = trim_index(_tail_index + 1);
  } else {
    _head_index = trim_index(_head_index + 1);
    ++_no_entries;
  }
  _array[_head_index] = G1MMUTrackerQueueElem(start, end);
}

// basically the _internal call does not remove expired entries
// this is for trying things out in the future and a couple
// of other places (debugging)

double G1MMUTrackerQueue::longest_pause(double current_time) {
  if (_DISABLE_MMU)
    return _max_gc_time;

  MutexLockerEx x(MMUTracker_lock, Mutex::_no_safepoint_check_flag);
  remove_expired_entries(current_time);

  return longest_pause_internal(current_time);
}

double G1MMUTrackerQueue::longest_pause_internal(double current_time) {
  double target_time = _max_gc_time;

  while( 1 ) {
    double gc_time =
      calculate_gc_time(current_time + target_time);
    double diff = target_time + gc_time - _max_gc_time;
    if (!is_double_leq_0(diff)) {
      target_time -= diff;
      if (is_double_leq_0(target_time)) {
        target_time = -1.0;
        break;
      }
    } else {
      break;
    }
  }

  return target_time;
}

// basically the _internal call does not remove expired entries
// this is for trying things out in the future and a couple
// of other places (debugging)

double G1MMUTrackerQueue::when_sec(double current_time, double pause_time) {
  if (_DISABLE_MMU)
    return 0.0;

  MutexLockerEx x(MMUTracker_lock, Mutex::_no_safepoint_check_flag);
  remove_expired_entries(current_time);

  return when_internal(current_time, pause_time);
}

double G1MMUTrackerQueue::when_internal(double current_time,
                                        double pause_time) {
  // if the pause is over the maximum, just assume that it's the maximum
  double adjusted_pause_time =
    (pause_time > max_gc_time()) ? max_gc_time() : pause_time;
  double earliest_end = current_time + adjusted_pause_time;
  double limit = earliest_end - _time_slice;
  double gc_time = calculate_gc_time(earliest_end);
  double diff = gc_time + adjusted_pause_time - max_gc_time();
  if (is_double_leq_0(diff))
    return 0.0;

  int index = _tail_index;
  while ( 1 ) {
    G1MMUTrackerQueueElem *elem = &_array[index];
    if (elem->end_time() > limit) {
      if (elem->start_time() > limit)
        diff -= elem->duration();
      else
        diff -= elem->end_time() - limit;
      if (is_double_leq_0(diff))
        return  elem->end_time() + diff + _time_slice - adjusted_pause_time - current_time;
    }
    index = trim_index(index+1);
    guarantee(index != trim_index(_head_index + 1), "should not go past head");
  }
}