8342382: Implement JEP 522: G1 GC: Improve Throughput by Reducing Synchronization

src/hotspot/share/gc/g1/g1ConcurrentRefine.cpp

@@ -220,11 +220,11 @@ bool G1ConcurrentRefineSweepState::swap_java_threads_ct() {
     Handshake::execute(&cl);
   }
 
-  return advance_state(State::SwapGCThreadsCT);
+  return advance_state(State::SynchronizeGCThreads);
 }
 
 bool G1ConcurrentRefineSweepState::swap_gc_threads_ct() {
-  assert_state(State::SwapGCThreadsCT);
+  assert_state(State::SynchronizeGCThreads);
 
   set_state_start_time();
 

src/hotspot/share/gc/g1/g1ConcurrentRefine.hpp

@@ -113,7 +113,7 @@ class G1ConcurrentRefineSweepState {
     Idle,                        // Refinement is doing nothing.
     SwapGlobalCT,                // Swap global card table.
     SwapJavaThreadsCT,           // Swap java thread's card tables.
-    SwapGCThreadsCT,             // Swap GC thread's card tables.
+    SynchronizeGCThreads,        // Synchronize GC thread's memory view.
     SnapshotHeap,                // Take a snapshot of the region's top() values.
     SweepRT,                     // Sweep the refinement table for pending (dirty) cards.
     CompleteRefineWork,          // Cleanup of refinement work, reset to idle.

src/hotspot/share/gc/g1/g1ConcurrentRefineThread.hpp

@@ -33,8 +33,8 @@
 // Forward Decl.
 class G1ConcurrentRefine;
 
-// One or more G1 Concurrent Refinement Threads may be active if concurrent
-// refinement is in progress.
+// Concurrent refinement control thread watching card mark accrual on the card
+// and starting refinement work.
 class G1ConcurrentRefineThread: public ConcurrentGCThread {
   friend class VMStructs;
   friend class G1CollectedHeap;

src/hotspot/share/gc/g1/g1ConcurrentRefineWorkTask.cpp

@@ -53,29 +53,38 @@
     assert(refinement_i == card_i, "indexes are not same %zu %zu", refinement_i, card_i);
 #endif
     G1RemSet::RefineResult res = _rem_set->refine_card_concurrently(source_card, _worker_id);
-    // Gather statistics.
-    if (res == G1RemSet::CouldNotParse) {
-      // Could not refine - redirty with the original value.
-      *dest_card = *source_card;
-      _refine_stats.inc_cards_not_parsable();
-    } else if (res == G1RemSet::AlreadyToCSet) {
-      *dest_card = G1CardTable::g1_to_cset_card;
-      _refine_stats.inc_cards_already_refer_to_cset();
-    } else if (res == G1RemSet::HasRefToCSet) {
-      *dest_card = G1CardTable::g1_to_cset_card;
-      _refine_stats.inc_cards_refer_to_cset();
-    } else if (res == G1RemSet::NoInteresting) {
-      _refine_stats.inc_cards_clean_again();
+    // Gather statistics based on the result.
+    switch (res) {
+      case G1RemSet::HasRefToCSet: {
+        *dest_card = G1CardTable::g1_to_cset_card;
+        _refine_stats.inc_cards_refer_to_cset();
+        break;
+      }
+      case G1RemSet::AlreadyToCSet: {
+        *dest_card = G1CardTable::g1_to_cset_card;
+        _refine_stats.inc_cards_already_refer_to_cset();
+        break;
+      }
+      case G1RemSet::NoInteresting: {
+        _refine_stats.inc_cards_clean_again();
+        break;
+      }
+      case G1RemSet::CouldNotParse: {
+        // Could not refine - redirty with the original value.
+        *dest_card = *source_card;
+        _refine_stats.inc_cards_not_parsable();
+        break;
+      }
+      case G1RemSet::HasRefToOld : break; // Nothing special to do.
     }
     // Clean card on source card table.
     *source_card = G1CardTable::clean_card_val();
   }
 
-  size_t do_claimed_block(CardValue* dirty_l, CardValue* dirty_r, CardValue* dest_card) {
+  void do_claimed_block(CardValue* dirty_l, CardValue* dirty_r, CardValue* dest_card) {
     for (CardValue* source = dirty_l; source < dirty_r; ++source, ++dest_card) {
       do_dirty_card(source, dest_card);
     }
-    return pointer_delta(dirty_r, dirty_l, sizeof(CardValue));
   }
 
 public:
@@ -125,7 +134,10 @@
       size_t scanned = 0;
       scanner.on_dirty_cards([&] (CardValue* dirty_l, CardValue* dirty_r) {
                                jlong refine_start = os::elapsed_counter();
-                               scanned += do_claimed_block(dirty_l, dirty_r, dest_card + pointer_delta(dirty_l, start_card, sizeof(CardValue)));
+
+                               do_claimed_block(dirty_l, dirty_r, dest_card + pointer_delta(dirty_l, start_card, sizeof(CardValue)));
+                               scanned += pointer_delta(dirty_r, dirty_l, sizeof(CardValue));
+
                                _refine_stats.inc_refine_duration(os::elapsed_counter() - refine_start);
                              });