src/share/vm/gc_implementation/g1/g1HotCardCache.hpp

rev 7695 : 8069273: Reduce Hot Card Cache Lock contention
Reviewed-by: tschatzl

*** 52,76 ****
  //
  // This can significantly reduce the overhead of the write barrier
  // code, increasing throughput.
  
  class G1HotCardCache: public CHeapObj<mtGC> {
    G1CollectedHeap*   _g1h;
  
    // The card cache table
    jbyte**      _hot_cache;
  
!   int          _hot_cache_size;
!   int          _n_hot;
!   int          _hot_cache_idx;
  
    int          _hot_cache_par_chunk_size;
-   volatile int _hot_cache_par_claimed_idx;
  
!   bool         _use_cache;
  
!   G1CardCounts _card_counts;
  
    // The number of cached cards a thread claims when flushing the cache
    static const int ClaimChunkSize = 32;
  
    bool default_use_cache() const {
--- 52,85 ----
  //
  // This can significantly reduce the overhead of the write barrier
  // code, increasing throughput.
  
  class G1HotCardCache: public CHeapObj<mtGC> {
+ 
    G1CollectedHeap*  _g1h;
  
+   bool              _use_cache;
+ 
+   G1CardCounts      _card_counts;
+ 
    // The card cache table
    jbyte**           _hot_cache;
  
!   intptr_t          _hot_cache_size;
  
    int               _hot_cache_par_chunk_size;
  
!   // Avoids false sharing when concurrently updating _hot_cache_idx or
!   // _hot_cache_par_claimed_idx. These are never updated at the same time
!   // thus it's not necessary to separate them as well
!   char _pad_before[DEFAULT_CACHE_LINE_SIZE];
  
!   volatile intptr_t _hot_cache_idx;
!   
!   volatile intptr_t _hot_cache_par_claimed_idx;
! 
!   char _pad_after[DEFAULT_CACHE_LINE_SIZE];
  
    // The number of cached cards a thread claims when flushing the cache
    static const int ClaimChunkSize = 32;
  
    bool default_use_cache() const {
*** 111,124 ****
  
    // Resets the hot card cache and discards the entries.
    void reset_hot_cache() {
      assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
      assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
!     _hot_cache_idx = 0; _n_hot = 0;
    }
  
!   bool hot_cache_is_empty() { return _n_hot == 0; }
  
    // Zeros the values in the card counts table for entire committed heap
    void reset_card_counts();
  
    // Zeros the values in the card counts table for the given region
--- 120,136 ----
  
    // Resets the hot card cache and discards the entries.
    void reset_hot_cache() {
      assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
      assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
!     _hot_cache_idx = 0;
!     for (intptr_t i = 0; i < _hot_cache_size; i++) {
!         _hot_cache[i] = NULL;
!     }
    }
  
!   bool hot_cache_is_empty() { return _hot_cache[0] == NULL; }
  
    // Zeros the values in the card counts table for entire committed heap
    void reset_card_counts();
  
    // Zeros the values in the card counts table for the given region