# HG changeset patch
# User jcoomes
# Date 1279341201 25200
# Node ID a93a9eda13f7b61fa6d638ea7c9a7b89f7bb75fb
# Parent  1a1ce2076047740e842216147748094d1a5dd1a3
6962947: shared TaskQueue statistics
Reviewed-by: tonyp, ysr

diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
--- a/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp	Fri Jul 16 21:33:21 2010 -0700
@@ -664,19 +664,14 @@
         return;
       }
 
-      // XXX use a global constant instead of 64!
-      typedef struct OopTaskQueuePadded {
-        OopTaskQueue work_queue;
-        char pad[64 - sizeof(OopTaskQueue)];  // prevent false sharing
-      } OopTaskQueuePadded;
-
+      typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
       for (i = 0; i < num_queues; i++) {
-        OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
-        if (q_padded == NULL) {
+        PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
+        if (q == NULL) {
           warning("work_queue allocation failure.");
           return;
         }
-        _task_queues->register_queue(i, &q_padded->work_queue);
+        _task_queues->register_queue(i, q);
       }
       for (i = 0; i < num_queues; i++) {
         _task_queues->queue(i)->initialize();
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/parNew/parNewGeneration.cpp
--- a/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Fri Jul 16 21:33:21 2010 -0700
@@ -539,10 +539,9 @@
   guarantee(_task_queues != NULL, "task_queues allocation failure.");
 
   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
-    ObjToScanQueuePadded *q_padded = new ObjToScanQueuePadded();
-    guarantee(q_padded != NULL, "work_queue Allocation failure.");
-
-    _task_queues->register_queue(i1, &q_padded->work_queue);
+    ObjToScanQueue *q = new ObjToScanQueue();
+    guarantee(q != NULL, "work_queue Allocation failure.");
+    _task_queues->register_queue(i1, q);
   }
 
   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/parNew/parNewGeneration.hpp
--- a/src/share/vm/gc_implementation/parNew/parNewGeneration.hpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/parNew/parNewGeneration.hpp	Fri Jul 16 21:33:21 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2009, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -33,8 +33,8 @@
 // but they must be here to allow ParScanClosure::do_oop_work to be defined
 // in genOopClosures.inline.hpp.
 
-typedef OopTaskQueue       ObjToScanQueue;
-typedef OopTaskQueueSet    ObjToScanQueueSet;
+typedef Padded<OopTaskQueue> ObjToScanQueue;
+typedef GenericTaskQueueSet<ObjToScanQueue> ObjToScanQueueSet;
 
 // Enable this to get push/pop/steal stats.
 const int PAR_STATS_ENABLED = 0;
@@ -304,12 +304,6 @@
   friend class ParEvacuateFollowersClosure;
 
  private:
-  // XXX use a global constant instead of 64!
-  struct ObjToScanQueuePadded {
-        ObjToScanQueue work_queue;
-        char pad[64 - sizeof(ObjToScanQueue)];  // prevent false sharing
-  };
-
   // The per-worker-thread work queues
   ObjToScanQueueSet* _task_queues;
 
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/parNew/parOopClosures.hpp
--- a/src/share/vm/gc_implementation/parNew/parOopClosures.hpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/parNew/parOopClosures.hpp	Fri Jul 16 21:33:21 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -26,7 +26,8 @@
 
 class ParScanThreadState;
 class ParNewGeneration;
-typedef OopTaskQueueSet ObjToScanQueueSet;
+typedef Padded<OopTaskQueue> ObjToScanQueue;
+typedef GenericTaskQueueSet<ObjToScanQueue> ObjToScanQueueSet;
 class ParallelTaskTerminator;
 
 class ParScanClosure: public OopsInGenClosure {
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.cpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.cpp	Fri Jul 16 21:33:21 2010 -0700
@@ -90,10 +90,7 @@
 }
 
 void PSPromotionManager::post_scavenge() {
-#if PS_PM_STATS
-  print_stats();
-#endif // PS_PM_STATS
-
+  TASKQUEUE_STATS_ONLY(if (PrintGCDetails && ParallelGCVerbose) print_stats());
   for (uint i = 0; i < ParallelGCThreads + 1; i++) {
     PSPromotionManager* manager = manager_array(i);
     if (UseDepthFirstScavengeOrder) {
@@ -105,37 +102,58 @@
   }
 }
 
-#if PS_PM_STATS
-
+#if TASKQUEUE_STATS
 void
-PSPromotionManager::print_stats(uint i) {
-  tty->print_cr("---- GC Worker %2d Stats", i);
-  tty->print_cr("    total pushes            %8d", _total_pushes);
-  tty->print_cr("    masked pushes           %8d", _masked_pushes);
-  tty->print_cr("    overflow pushes         %8d", _overflow_pushes);
-  tty->print_cr("    max overflow length     %8d", _max_overflow_length);
-  tty->print_cr("");
-  tty->print_cr("    arrays chunked          %8d", _arrays_chunked);
-  tty->print_cr("    array chunks processed  %8d", _array_chunks_processed);
-  tty->print_cr("");
-  tty->print_cr("    total steals            %8d", _total_steals);
-  tty->print_cr("    masked steals           %8d", _masked_steals);
-  tty->print_cr("");
+PSPromotionManager::print_taskqueue_stats(uint i) const {
+  const TaskQueueStats& stats = depth_first() ?
+    _claimed_stack_depth.stats : _claimed_stack_breadth.stats;
+  tty->print("%3u ", i);
+  stats.print();
+  tty->cr();
 }
 
 void
+PSPromotionManager::print_local_stats(uint i) const {
+  #define FMT " " SIZE_FORMAT_W(10)
+  tty->print_cr("%3u" FMT FMT FMT FMT, i, _masked_pushes, _masked_steals,
+                _arrays_chunked, _array_chunks_processed);
+  #undef FMT
+}
+
+static const char* const pm_stats_hdr[] = {
+  "    --------masked-------     arrays      array",
+  "thr       push      steal    chunked     chunks",
+  "--- ---------- ---------- ---------- ----------"
+};
+
+void
 PSPromotionManager::print_stats() {
-  tty->print_cr("== GC Tasks Stats (%s), GC %3d",
-                (UseDepthFirstScavengeOrder) ? "Depth-First" : "Breadth-First",
+  const bool df = UseDepthFirstScavengeOrder;
+  tty->print_cr("== GC Task Stats (%s-First), GC %3d", df ? "Depth" : "Breadth",
                 Universe::heap()->total_collections());
 
-  for (uint i = 0; i < ParallelGCThreads+1; ++i) {
-    PSPromotionManager* manager = manager_array(i);
-    manager->print_stats(i);
+  tty->print("thr "); TaskQueueStats::print_header(1); tty->cr();
+  tty->print("--- "); TaskQueueStats::print_header(2); tty->cr();
+  for (uint i = 0; i < ParallelGCThreads + 1; ++i) {
+    manager_array(i)->print_taskqueue_stats(i);
+  }
+
+  const uint hlines = sizeof(pm_stats_hdr) / sizeof(pm_stats_hdr[0]);
+  for (uint i = 0; i < hlines; ++i) tty->print_cr(pm_stats_hdr[i]);
+  for (uint i = 0; i < ParallelGCThreads + 1; ++i) {
+    manager_array(i)->print_local_stats(i);
   }
 }
 
-#endif // PS_PM_STATS
+void
+PSPromotionManager::reset_stats() {
+  TaskQueueStats& stats = depth_first() ?
+    claimed_stack_depth()->stats : claimed_stack_breadth()->stats;
+  stats.reset();
+  _masked_pushes = _masked_steals = 0;
+  _arrays_chunked = _array_chunks_processed = 0;
+}
+#endif // TASKQUEUE_STATS
 
 PSPromotionManager::PSPromotionManager() {
   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
@@ -189,16 +207,7 @@
 
   _prefetch_queue.clear();
 
-#if PS_PM_STATS
-  _total_pushes = 0;
-  _masked_pushes = 0;
-  _overflow_pushes = 0;
-  _max_overflow_length = 0;
-  _arrays_chunked = 0;
-  _array_chunks_processed = 0;
-  _total_steals = 0;
-  _masked_steals = 0;
-#endif // PS_PM_STATS
+  TASKQUEUE_STATS_ONLY(reset_stats());
 }
 
 
@@ -423,14 +432,9 @@
             new_obj->is_objArray() &&
             PSChunkLargeArrays) {
           // we'll chunk it
-#if PS_PM_STATS
-          ++_arrays_chunked;
-#endif // PS_PM_STATS
           oop* const masked_o = mask_chunked_array_oop(o);
           push_depth(masked_o);
-#if PS_PM_STATS
-          ++_masked_pushes;
-#endif // PS_PM_STATS
+          TASKQUEUE_STATS_ONLY(++_arrays_chunked; ++_masked_pushes);
         } else {
           // we'll just push its contents
           new_obj->push_contents(this);
@@ -494,9 +498,7 @@
   assert(old->is_objArray(), "invariant");
   assert(old->is_forwarded(), "invariant");
 
-#if PS_PM_STATS
-  ++_array_chunks_processed;
-#endif // PS_PM_STATS
+  TASKQUEUE_STATS_ONLY(++_array_chunks_processed);
 
   oop const obj = old->forwardee();
 
@@ -508,9 +510,7 @@
     assert(start > 0, "invariant");
     arrayOop(old)->set_length(start);
     push_depth(mask_chunked_array_oop(old));
-#if PS_PM_STATS
-    ++_masked_pushes;
-#endif // PS_PM_STATS
+    TASKQUEUE_STATS_ONLY(++_masked_pushes);
   } else {
     // this is the final chunk for this array
     start = 0;
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.hpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.hpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.hpp	Fri Jul 16 21:33:21 2010 -0700
@@ -42,8 +42,6 @@
 class PSOldGen;
 class ParCompactionManager;
 
-#define PS_PM_STATS         0
-
 class PSPromotionManager : public CHeapObj {
   friend class PSScavenge;
   friend class PSRefProcTaskExecutor;
@@ -54,22 +52,18 @@
   static PSOldGen*                    _old_gen;
   static MutableSpace*                _young_space;
 
-#if PS_PM_STATS
-  uint                                _total_pushes;
-  uint                                _masked_pushes;
-
-  uint                                _overflow_pushes;
-  uint                                _max_overflow_length;
+#if TASKQUEUE_STATS
+  size_t                              _masked_pushes;
+  size_t                              _masked_steals;
+  size_t                              _arrays_chunked;
+  size_t                              _array_chunks_processed;
 
-  uint                                _arrays_chunked;
-  uint                                _array_chunks_processed;
+  void print_taskqueue_stats(uint i) const;
+  void print_local_stats(uint i) const;
+  static void print_stats();
 
-  uint                                _total_steals;
-  uint                                _masked_steals;
-
-  void print_stats(uint i);
-  static void print_stats();
-#endif // PS_PM_STATS
+  void reset_stats();
+#endif // TASKQUEUE_STATS
 
   PSYoungPromotionLAB                 _young_lab;
   PSOldPromotionLAB                   _old_lab;
@@ -143,42 +137,12 @@
 
   template <class T> void push_depth(T* p) {
     assert(depth_first(), "pre-condition");
-
-#if PS_PM_STATS
-    ++_total_pushes;
-    int stack_length = claimed_stack_depth()->overflow_stack()->length();
-#endif // PS_PM_STATS
-
     claimed_stack_depth()->push(p);
-
-#if PS_PM_STATS
-    if (claimed_stack_depth()->overflow_stack()->length() != stack_length) {
-      ++_overflow_pushes;
-      if ((uint)stack_length + 1 > _max_overflow_length) {
-        _max_overflow_length = (uint)stack_length + 1;
-      }
-    }
-#endif // PS_PM_STATS
   }
 
   void push_breadth(oop o) {
     assert(!depth_first(), "pre-condition");
-
-#if PS_PM_STATS
-    ++_total_pushes;
-    int stack_length = claimed_stack_breadth()->overflow_stack()->length();
-#endif // PS_PM_STATS
-
     claimed_stack_breadth()->push(o);
-
-#if PS_PM_STATS
-    if (claimed_stack_breadth()->overflow_stack()->length() != stack_length) {
-      ++_overflow_pushes;
-      if ((uint)stack_length + 1 > _max_overflow_length) {
-        _max_overflow_length = (uint)stack_length + 1;
-      }
-    }
-#endif // PS_PM_STATS
   }
 
  protected:
@@ -256,12 +220,5 @@
   template <class T> inline void claim_or_forward_depth(T* p);
   template <class T> inline void claim_or_forward_breadth(T* p);
 
-#if PS_PM_STATS
-  void increment_steals(oop* p = NULL) {
-    _total_steals += 1;
-    if (p != NULL && is_oop_masked(p)) {
-      _masked_steals += 1;
-    }
-  }
-#endif // PS_PM_STATS
+  TASKQUEUE_STATS_ONLY(inline void record_steal(StarTask& p);)
 };
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.inline.hpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.inline.hpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.inline.hpp	Fri Jul 16 21:33:21 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2002, 2008, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2002, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -124,3 +124,11 @@
     }
   }
 }
+
+#if TASKQUEUE_STATS
+void PSPromotionManager::record_steal(StarTask& p) {
+  if (is_oop_masked(p)) {
+    ++_masked_steals;
+  }
+}
+#endif // TASKQUEUE_STATS
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/gc_implementation/parallelScavenge/psTasks.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psTasks.cpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psTasks.cpp	Fri Jul 16 21:33:21 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2002, 2008, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2002, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -148,9 +148,7 @@
     while(true) {
       StarTask p;
       if (PSPromotionManager::steal_depth(which, &random_seed, p)) {
-#if PS_PM_STATS
-        pm->increment_steals(p);
-#endif // PS_PM_STATS
+        TASKQUEUE_STATS_ONLY(pm->record_steal(p));
         pm->process_popped_location_depth(p);
         pm->drain_stacks_depth(true);
       } else {
@@ -163,9 +161,6 @@
     while(true) {
       oop obj;
       if (PSPromotionManager::steal_breadth(which, &random_seed, obj)) {
-#if PS_PM_STATS
-        pm->increment_steals();
-#endif // PS_PM_STATS
         obj->copy_contents(pm);
         pm->drain_stacks_breadth(true);
       } else {
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/utilities/globalDefinitions.hpp
--- a/src/share/vm/utilities/globalDefinitions.hpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/utilities/globalDefinitions.hpp	Fri Jul 16 21:33:21 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2009, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -345,6 +345,35 @@
   return align_size_up(offset, HeapWordsPerLong);
 }
 
+// The expected size in bytes of a cache line, used to pad data structures.
+#define DEFAULT_CACHE_LINE_SIZE 64
+
+// Bytes needed to pad type to avoid cache-line sharing; alignment should be the
+// expected cache line size (a power of two).  The first addend avoids sharing
+// when the start address is not a multiple of alignment; the second maintains
+// alignment of starting addresses that happen to be a multiple.
+#define PADDING_SIZE(type, alignment)                           \
+  ((alignment) + align_size_up_(sizeof(type), alignment))
+
+// Templates to create a subclass padded to avoid cache line sharing.  These are
+// effective only when applied to derived-most (leaf) classes.
+
+// When no args are passed to the base ctor.
+template <class T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
+class Padded: public T {
+private:
+  char _pad_buf_[PADDING_SIZE(T, alignment)];
+};
+
+// When either 0 or 1 args may be passed to the base ctor.
+template <class T, typename Arg1T, size_t alignment = DEFAULT_CACHE_LINE_SIZE>
+class Padded01: public T {
+public:
+  Padded01(): T() { }
+  Padded01(Arg1T arg1): T(arg1) { }
+private:
+  char _pad_buf_[PADDING_SIZE(T, alignment)];
+};
 
 //----------------------------------------------------------------------------------------------------
 // Utility macros for compilers
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/utilities/taskqueue.cpp
--- a/src/share/vm/utilities/taskqueue.cpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/utilities/taskqueue.cpp	Fri Jul 16 21:33:21 2010 -0700
@@ -31,6 +31,48 @@
 uint ParallelTaskTerminator::_total_peeks = 0;
 #endif
 
+#if TASKQUEUE_STATS
+const char * const TaskQueueStats::_names[last_stat_id] = {
+  "qpush", "qpop", "qpop-s", "qattempt", "qsteal", "opush", "omax"
+};
+
+void TaskQueueStats::print_header(unsigned int line, outputStream* const stream,
+                                  unsigned int width)
+{
+  // Use a width w: 1 <= w <= max_width
+  const unsigned int max_width = 40;
+  const unsigned int w = MAX2(MIN2(width, max_width), 1U);
+
+  if (line == 0) { // spaces equal in width to the header
+    const unsigned int hdr_width = w * last_stat_id + last_stat_id - 1;
+    stream->print("%*s", hdr_width, " ");
+  } else if (line == 1) { // labels
+    stream->print("%*s", w, _names[0]);
+    for (unsigned int i = 1; i < last_stat_id; ++i) {
+      stream->print(" %*s", w, _names[i]);
+    }
+  } else if (line == 2) { // dashed lines
+    char dashes[max_width + 1];
+    memset(dashes, '-', w);
+    dashes[w] = '\0';
+    stream->print("%s", dashes);
+    for (unsigned int i = 1; i < last_stat_id; ++i) {
+      stream->print(" %s", dashes);
+    }
+  }
+}
+
+void TaskQueueStats::print(outputStream* stream, unsigned int width) const
+{
+  #define FMT SIZE_FORMAT_W(*)
+  stream->print(FMT, width, _stats[0]);
+  for (unsigned int i = 1; i < last_stat_id; ++i) {
+    stream->print(" " FMT, width, _stats[i]);
+  }
+  #undef FMT
+}
+#endif // TASKQUEUE_STATS
+
 int TaskQueueSetSuper::randomParkAndMiller(int *seed0) {
   const int a =      16807;
   const int m = 2147483647;
diff -r 1a1ce2076047 -r a93a9eda13f7 src/share/vm/utilities/taskqueue.hpp
--- a/src/share/vm/utilities/taskqueue.hpp	Fri Jul 16 10:09:15 2010 -0700
+++ b/src/share/vm/utilities/taskqueue.hpp	Fri Jul 16 21:33:21 2010 -0700
@@ -22,6 +22,72 @@
  *
  */
 
+// Simple TaskQueue stats that are collected by default in debug builds.
+
+#if !defined(TASKQUEUE_STATS) && defined(ASSERT)
+#define TASKQUEUE_STATS 1
+#elif !defined(TASKQUEUE_STATS)
+#define TASKQUEUE_STATS 0
+#endif
+
+#if TASKQUEUE_STATS
+#define TASKQUEUE_STATS_ONLY(code) code
+#else
+#define TASKQUEUE_STATS_ONLY(code)
+#endif // TASKQUEUE_STATS
+
+#if TASKQUEUE_STATS
+class TaskQueueStats {
+public:
+  enum StatId {
+    push,             // number of taskqueue pushes
+    pop,              // number of taskqueue pops
+    pop_slow,         // subset of taskqueue pops that were done slow-path
+    steal_attempt,    // number of taskqueue steal attempts
+    steal,            // number of taskqueue steals
+    overflow,         // number of overflow pushes
+    overflow_max_len, // max length of overflow stack
+    last_stat_id
+  };
+
+public:
+  inline TaskQueueStats()       { reset(); }
+
+  inline void record_push()     { ++_stats[push]; }
+  inline void record_pop()      { ++_stats[pop]; }
+  inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; }
+  inline void record_steal(bool success);
+  inline void record_overflow(size_t new_length);
+
+  inline size_t get(StatId id) const { return _stats[id]; }
+  inline const size_t* get() const   { return _stats; }
+
+  inline void reset();
+
+  static void print_header(unsigned int line, outputStream* const stream = tty,
+                           unsigned int width = 10);
+  void print(outputStream* const stream = tty, unsigned int width = 10) const;
+
+private:
+  size_t                    _stats[last_stat_id];
+  static const char * const _names[last_stat_id];
+};
+
+void TaskQueueStats::record_steal(bool success) {
+  ++_stats[steal_attempt];
+  if (success) ++_stats[steal];
+}
+
+void TaskQueueStats::record_overflow(size_t new_len) {
+  ++_stats[overflow];
+  if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
+}
+
+void TaskQueueStats::reset() {
+  memset(_stats, 0, sizeof(_stats));
+}
+#endif // TASKQUEUE_STATS
+
 template <unsigned int N>
 class TaskQueueSuper: public CHeapObj {
 protected:
@@ -135,6 +201,8 @@
 
   // Total size of queue.
   static const uint total_size() { return N; }
+
+  TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
 };
 
 template<class E, unsigned int N = TASKQUEUE_SIZE>
@@ -152,6 +220,7 @@
 public:
   using TaskQueueSuper<N>::max_elems;
   using TaskQueueSuper<N>::size;
+  TASKQUEUE_STATS_ONLY(using TaskQueueSuper<N>::stats;)
 
 private:
   // Slow paths for push, pop_local.  (pop_global has no fast path.)
@@ -224,14 +293,14 @@
     // g++ complains if the volatile result of the assignment is unused.
     const_cast<E&>(_elems[localBot] = t);
     OrderAccess::release_store(&_bottom, increment_index(localBot));
+    TASKQUEUE_STATS_ONLY(stats.record_push());
     return true;
   }
   return false;
 }
 
 template<class E, unsigned int N>
-bool GenericTaskQueue<E, N>::
-pop_local_slow(uint localBot, Age oldAge) {
+bool GenericTaskQueue<E, N>::pop_local_slow(uint localBot, Age oldAge) {
   // This queue was observed to contain exactly one element; either this
   // thread will claim it, or a competing "pop_global".  In either case,
   // the queue will be logically empty afterwards.  Create a new Age value
@@ -251,6 +320,7 @@
     if (tempAge == oldAge) {
       // We win.
       assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
+      TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
       return true;
     }
   }
@@ -306,6 +376,8 @@
   typedef GrowableArray<E>       overflow_t;
   typedef GenericTaskQueue<E, N> taskqueue_t;
 
+  TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
+
   OverflowTaskQueue();
   ~OverflowTaskQueue();
   void initialize();
@@ -356,6 +428,7 @@
 {
   if (!taskqueue_t::push(t)) {
     overflow_stack()->push(t);
+    TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->length()));
   }
   return true;
 }
@@ -424,9 +497,13 @@
 
 template<class T> bool
 GenericTaskQueueSet<T>::steal(uint queue_num, int* seed, E& t) {
-  for (uint i = 0; i < 2 * _n; i++)
-    if (steal_best_of_2(queue_num, seed, t))
+  for (uint i = 0; i < 2 * _n; i++) {
+    if (steal_best_of_2(queue_num, seed, t)) {
+      TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
       return true;
+    }
+  }
+  TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
   return false;
 }
 
@@ -574,6 +651,7 @@
     // g++ complains if the volatile result of the assignment is unused.
     const_cast<E&>(_elems[localBot] = t);
     OrderAccess::release_store(&_bottom, increment_index(localBot));
+    TASKQUEUE_STATS_ONLY(stats.record_push());
     return true;
   } else {
     return push_slow(t, dirty_n_elems);
@@ -603,6 +681,7 @@
   idx_t tp = _age.top();    // XXX
   if (size(localBot, tp) > 0) {
     assert(dirty_size(localBot, tp) != N - 1, "sanity");
+    TASKQUEUE_STATS_ONLY(stats.record_pop());
     return true;
   } else {
     // Otherwise, the queue contained exactly one element; we take the slow