rev 7695 : 8069273: Reduce Hot Card Cache Lock contention
Reviewed-by: tschatzl
rev 7696 : [mq]: atomicadd

   1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP
  27 
  28 #include "gc_implementation/g1/g1_globals.hpp"
  29 #include "gc_implementation/g1/g1CardCounts.hpp"
  30 #include "memory/allocation.hpp"
  31 #include "runtime/safepoint.hpp"
  32 #include "runtime/thread.inline.hpp"
  33 #include "utilities/globalDefinitions.hpp"
  34 
  35 class DirtyCardQueue;
  36 class G1CollectedHeap;
  37 class G1RemSet;
  38 class HeapRegion;
  39 
  40 // An evicting cache of cards that have been logged by the G1 post
  41 // write barrier. Placing a card in the cache delays the refinement
  42 // of the card until the card is evicted, or the cache is drained
  43 // during the next evacuation pause.
  44 //
  45 // The first thing the G1 post write barrier does is to check whether
  46 // the card containing the updated pointer is already dirty and, if
  47 // so, skips the remaining code in the barrier.
  48 //
  49 // Delaying the refinement of a card will make the card fail the
  50 // first is_dirty check in the write barrier, skipping the remainder
  51 // of the write barrier.
  52 //
  53 // This can significantly reduce the overhead of the write barrier
  54 // code, increasing throughput.
  55 
  56 class G1HotCardCache: public CHeapObj<mtGC> {
  57 
  58   G1CollectedHeap*  _g1h;
  59 
  60   bool              _use_cache;
  61 
  62   G1CardCounts      _card_counts;
  63 
  64   // The card cache table
  65   jbyte**           _hot_cache;
  66 
  67   size_t            _hot_cache_size;


  68 
  69   int               _hot_cache_par_chunk_size;

  70 
  71   // Avoids false sharing when concurrently updating _hot_cache_idx or
  72   // _hot_cache_par_claimed_idx. These are never updated at the same time
  73   // thus it's not necessary to separate them as well
  74   char _pad_before[DEFAULT_CACHE_LINE_SIZE];
  75 
  76   volatile size_t _hot_cache_idx;
  77   
  78   volatile size_t _hot_cache_par_claimed_idx;
  79 
  80   char _pad_after[DEFAULT_CACHE_LINE_SIZE];
  81 
  82   // The number of cached cards a thread claims when flushing the cache
  83   static const int ClaimChunkSize = 32;
  84 
  85   bool default_use_cache() const {
  86     return (G1ConcRSLogCacheSize > 0);
  87   }
  88 
  89  public:
  90   G1HotCardCache(G1CollectedHeap* g1h);
  91   ~G1HotCardCache();
  92 
  93   void initialize(G1RegionToSpaceMapper* card_counts_storage);
  94 
  95   bool use_cache() { return _use_cache; }
  96 
  97   void set_use_cache(bool b) {
  98     _use_cache = (b ? default_use_cache() : false);
  99   }
 100 
 101   // Returns the card to be refined or NULL.
 102   //
 103   // Increments the count for given the card. if the card is not 'hot',
 104   // it is returned for immediate refining. Otherwise the card is
 105   // added to the hot card cache.
 106   // If there is enough room in the hot card cache for the card we're
 107   // adding, NULL is returned and no further action in needed.
 108   // If we evict a card from the cache to make room for the new card,
 109   // the evicted card is then returned for refinement.
 110   jbyte* insert(jbyte* card_ptr);
 111 
 112   // Refine the cards that have delayed as a result of
 113   // being in the cache.
 114   void drain(uint worker_i, G1RemSet* g1rs, DirtyCardQueue* into_cset_dcq);
 115 
 116   // Set up for parallel processing of the cards in the hot cache
 117   void reset_hot_cache_claimed_index() {
 118     _hot_cache_par_claimed_idx = 0;
 119   }
 120 
 121   // Resets the hot card cache and discards the entries.
 122   void reset_hot_cache() {
 123     assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
 124     assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
 125     _hot_cache_idx = 0;
 126     for (size_t i = 0; i < _hot_cache_size; i++) {
 127         _hot_cache[i] = NULL;
 128     }
 129   }
 130 
 131   bool hot_cache_is_empty() { return _hot_cache[0] == NULL; }
 132 
 133   // Zeros the values in the card counts table for entire committed heap
 134   void reset_card_counts();
 135 
 136   // Zeros the values in the card counts table for the given region
 137   void reset_card_counts(HeapRegion* hr);
 138 };
 139 
 140 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP
--- EOF ---