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

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

*** 34,47 ****
  
  void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
    if (default_use_cache()) {
      _use_cache = true;
  
!     _hot_cache_size = (1 << G1ConcRSLogCacheSize);
      _hot_cache = NEW_C_HEAP_ARRAY(jbyte*, _hot_cache_size, mtGC);
  
-     _n_hot = 0;
      _hot_cache_idx = 0;
  
      // For refining the cards in the hot cache in parallel
      _hot_cache_par_chunk_size = ClaimChunkSize;
      _hot_cache_par_claimed_idx = 0;
--- 34,49 ----
  
  void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
    if (default_use_cache()) {
      _use_cache = true;
  
!     _hot_cache_size = (size_t)1 << G1ConcRSLogCacheSize;
      _hot_cache = NEW_C_HEAP_ARRAY(jbyte*, _hot_cache_size, mtGC);
+     for (size_t i = 0; i < _hot_cache_size; i++) {
+       _hot_cache[i] = NULL;
+     }
  
      _hot_cache_idx = 0;
  
      // For refining the cards in the hot cache in parallel
      _hot_cache_par_chunk_size = ClaimChunkSize;
      _hot_cache_par_claimed_idx = 0;
*** 62,91 ****
    if (!_card_counts.is_hot(count)) {
      // The card is not hot so do not store it in the cache;
      // return it for immediate refining.
      return card_ptr;
    }
- 
    // Otherwise, the card is hot.
!   jbyte* res = NULL;
!   MutexLockerEx x(HotCardCache_lock, Mutex::_no_safepoint_check_flag);
!   if (_n_hot == _hot_cache_size) {
!     res = _hot_cache[_hot_cache_idx];
!     _n_hot--;
!   }
! 
!   // Now _n_hot < _hot_cache_size, and we can insert at _hot_cache_idx.
!   _hot_cache[_hot_cache_idx] = card_ptr;
!   _hot_cache_idx++;
! 
!   if (_hot_cache_idx == _hot_cache_size) {
!     // Wrap around
!     _hot_cache_idx = 0;
!   }
!   _n_hot++;
! 
!   return res;
  }
  
  void G1HotCardCache::drain(uint worker_i,
                             G1RemSet* g1rs,
                             DirtyCardQueue* into_cset_dcq) {
--- 64,88 ----
    if (!_card_counts.is_hot(count)) {
      // The card is not hot so do not store it in the cache;
      // return it for immediate refining.
      return card_ptr;
    }
    // Otherwise, the card is hot.
!   size_t index = Atomic::add(1, &_hot_cache_idx) - 1;
!   size_t masked_index = index & (_hot_cache_size - 1);
!   jbyte* current_ptr = _hot_cache[masked_index];
!   
!   // Try to store the new card pointer into the cache. Compare-and-swap to guard
!   // against the unlikely event of a race resulting in another card pointer to
!   // have already been written to the cache. In this case we will return
!   // card_ptr in favor of the other option, which would be starting over. This
!   // should be OK since card_ptr will likely be the older card already when/if
!   // this ever happens.
!   jbyte* previous_ptr = (jbyte*)Atomic::cmpxchg_ptr(card_ptr,
!                                                     &_hot_cache[masked_index],
!                                                     current_ptr);
!   return (previous_ptr == current_ptr) ? previous_ptr : card_ptr;
  }
  
  void G1HotCardCache::drain(uint worker_i,
                             G1RemSet* g1rs,
                             DirtyCardQueue* into_cset_dcq) {
*** 94,113 ****
      return;
    }
  
    assert(_hot_cache != NULL, "Logic");
    assert(!use_cache(), "cache should be disabled");
-   int start_idx;
- 
-   while ((start_idx = _hot_cache_par_claimed_idx) < _n_hot) { // read once
-     int end_idx = start_idx + _hot_cache_par_chunk_size;
  
!     if (start_idx ==
!         Atomic::cmpxchg(end_idx, &_hot_cache_par_claimed_idx, start_idx)) {
        // The current worker has successfully claimed the chunk [start_idx..end_idx)
!       end_idx = MIN2(end_idx, _n_hot);
!       for (int i = start_idx; i < end_idx; i++) {
          jbyte* card_ptr = _hot_cache[i];
          if (card_ptr != NULL) {
            if (g1rs->refine_card(card_ptr, worker_i, true)) {
              // The part of the heap spanned by the card contains references
              // that point into the current collection set.
--- 91,108 ----
      return;
    }
  
    assert(_hot_cache != NULL, "Logic");
    assert(!use_cache(), "cache should be disabled");
  
!   while (_hot_cache_par_claimed_idx < _hot_cache_size) {
!     size_t end_idx = Atomic::add(_hot_cache_par_chunk_size,
!                                  &_hot_cache_par_claimed_idx);
!     size_t start_idx = end_idx - _hot_cache_par_chunk_size;
      // The current worker has successfully claimed the chunk [start_idx..end_idx)
!     end_idx = MIN2(end_idx, _hot_cache_size);
!     for (size_t i = start_idx; i < end_idx; i++) {
        jbyte* card_ptr = _hot_cache[i];
        if (card_ptr != NULL) {
          if (g1rs->refine_card(card_ptr, worker_i, true)) {
            // The part of the heap spanned by the card contains references
            // that point into the current collection set.
*** 122,135 ****
              assert(worker_i < ParallelGCThreads,
                     err_msg("incorrect worker id: %u", worker_i));
  
              into_cset_dcq->enqueue(card_ptr);
            }
          }
        }
      }
!   }
    // The existing entries in the hot card cache, which were just refined
    // above, are discarded prior to re-enabling the cache near the end of the GC.
  }
  
  void G1HotCardCache::reset_card_counts(HeapRegion* hr) {
--- 117,132 ----
            assert(worker_i < ParallelGCThreads,
                   err_msg("incorrect worker id: %u", worker_i));
  
            into_cset_dcq->enqueue(card_ptr);
          }
+       } else {
+         break;
        }
      }
    }
!   
    // The existing entries in the hot card cache, which were just refined
    // above, are discarded prior to re-enabling the cache near the end of the GC.
  }
  
  void G1HotCardCache::reset_card_counts(HeapRegion* hr) {