# HG changeset patch
# User tonyp
# Date 1434579792 14400
#      Wed Jun 17 18:23:12 2015 -0400
# Node ID c6fa0403b66916939ecc63e2464c455487939041
# Parent  41e47efcd333a7b2e837a23d5f531953c167d861
8086056: ParNew: auto-tune ParGCCardsPerStrideChunk
Summary: Automatically calculate ParGCCardsPerStrideChunk based on the old gen capacity.
Reviewed-by:

diff --git a/src/share/vm/gc/cms/parNewGeneration.cpp b/src/share/vm/gc/cms/parNewGeneration.cpp
--- a/src/share/vm/gc/cms/parNewGeneration.cpp
+++ b/src/share/vm/gc/cms/parNewGeneration.cpp
@@ -620,7 +620,8 @@
   : DefNewGeneration(rs, initial_byte_size, level, "PCopy"),
   _overflow_list(NULL),
   _is_alive_closure(this),
-  _plab_stats(YoungPLABSize, PLABWeight)
+  _plab_stats(YoungPLABSize, PLABWeight),
+  _should_adjust_cards_per_stride(false)
 {
   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
   NOT_PRODUCT(_num_par_pushes = 0;)
@@ -658,6 +659,10 @@
     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
                                      ParallelGCThreads, CHECK);
   }
+
+  // we'll automatically calculate ParGCCardsPerStrideChunk if it has
+  // not been explicitly set on the command line
+  _should_adjust_cards_per_stride = FLAG_IS_DEFAULT(ParGCCardsPerStrideChunk);
 }
 #ifdef _MSC_VER
 #pragma warning( pop )
@@ -880,6 +885,42 @@
   NOT_PRODUCT(gch->reset_promotion_should_fail();)
 }
 
+void ParNewGeneration::adjust_cards_per_stride(const Generation& old_gen) {
+  if (!_should_adjust_cards_per_stride) return;
+
+  const size_t MinOldGenCapacity =      G;
+  const size_t MaxOldGenCapacity = 16 * G;
+  assert(MinOldGenCapacity <= MaxOldGenCapacity, "sanity");
+  const size_t OldGenCapacityDiff = MaxOldGenCapacity - MinOldGenCapacity;
+
+  const intx MinStrideChunkSize =   256;
+  const intx MaxStrideChunkSize = 8 * K;
+  assert(MinStrideChunkSize <= MaxStrideChunkSize, "sanity");
+  const intx StrideChunkSizeDiff = MaxStrideChunkSize - MinStrideChunkSize;
+
+  const size_t capacity = old_gen.capacity();
+  // adj_capacity = capacity bounded by {Min,Max}OldGenCapacity
+  size_t adj_capacity = capacity;
+  adj_capacity = MAX2(adj_capacity, MinOldGenCapacity);
+  adj_capacity = MIN2(adj_capacity, MaxOldGenCapacity);
+
+  const size_t capacity_offset = adj_capacity - MinOldGenCapacity;
+  assert(capacity_offset && capacity_offset <= OldGenCapacityDiff,
+         "sanity");
+  const double r = (double) capacity_offset / (double) OldGenCapacityDiff;
+  const intx stride_chunk_offset = (intx) (r * (double) StrideChunkSizeDiff);
+  const int stride_chunk_size_log =
+            log2_intptr((intptr_t) (MinStrideChunkSize + stride_chunk_offset));
+  const intx stride_chunk_size = (intx) 1 << stride_chunk_size_log;
+
+  assert(MinStrideChunkSize <= stride_chunk_size &&
+         stride_chunk_size <= MaxStrideChunkSize &&
+         is_power_of_2((intptr_t) stride_chunk_size),
+         err_msg("stride_chunk_size: "INTX_FORMAT, stride_chunk_size));
+
+  FLAG_SET_ERGO(intx, ParGCCardsPerStrideChunk, stride_chunk_size);
+}
+
 void ParNewGeneration::collect(bool   full,
                                bool   clear_all_soft_refs,
                                size_t size,
@@ -925,6 +966,7 @@
 
   age_table()->clear();
   to()->clear(SpaceDecorator::Mangle);
+  adjust_cards_per_stride(*_old_gen);
 
   gch->save_marks();
 
diff --git a/src/share/vm/gc/cms/parNewGeneration.hpp b/src/share/vm/gc/cms/parNewGeneration.hpp
--- a/src/share/vm/gc/cms/parNewGeneration.hpp
+++ b/src/share/vm/gc/cms/parNewGeneration.hpp
@@ -345,13 +345,19 @@
 
   void handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set);
 
- protected:
-
   bool _survivor_overflow;
 
   bool survivor_overflow() { return _survivor_overflow; }
   void set_survivor_overflow(bool v) { _survivor_overflow = v; }
 
+  // true -> should automatically calculate ParGCCardsPerStrideChunk
+  // before each young GC
+  bool _should_adjust_cards_per_stride;
+
+  // automatically calculate ParGCCardsPerStrideChunk based on the old
+  // gen capacity before each young GC
+  void adjust_cards_per_stride(const Generation& old_gen);
+
  public:
   ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level);