8258985: Parallel WeakProcessor may use too few threads

Use total workers rather than active.

Reviewed-by: tschatzl, ayang, sjohanss

Author: Kim Barrett

src/hotspot/share/gc/shared/weakProcessor.hpp

@@ -47,8 +47,9 @@ class WeakProcessor : AllStatic {
   // Visit all oop*s and apply the given closure.
   static void oops_do(OopClosure* closure);
 
-  // Parallel version.  Uses ergo_workers(), active workers, and
-  // phase_time's max_threads to determine the number of threads to use.
+  // Parallel version.  Uses ergo_workers() to determine the number of
+  // threads to use, limited by the total workers and phase_times'
+  // max_threads.
   // IsAlive must be derived from BoolObjectClosure.
   // KeepAlive must be derived from OopClosure.
   template<typename IsAlive, typename KeepAlive>
@@ -57,8 +58,9 @@ class WeakProcessor : AllStatic {
                            KeepAlive* keep_alive,
                            WeakProcessorPhaseTimes* phase_times);
 
-  // Convenience parallel version.  Uses ergo_workers() and active workers
-  // to determine the number of threads to run.  Implicitly logs phase times.
+  // Convenience parallel version.  Uses ergo_workers() to determine the
+  // number of threads to use, limited by the total workers.  Implicitly
+  // logs phase times.
   // IsAlive must be derived from BoolObjectClosure.
   // KeepAlive must be derived from OopClosure.
   template<typename IsAlive, typename KeepAlive>
@@ -67,7 +69,10 @@ class WeakProcessor : AllStatic {
                            KeepAlive* keep_alive,
                            uint indent_log);
 
+  // Uses the total number of weak references and ReferencesPerThread to
+  // determine the number of threads to use, limited by max_workers.
   static uint ergo_workers(uint max_workers);
+
   class Task;
 
 private:

src/hotspot/share/gc/shared/weakProcessor.inline.hpp

@@ -134,7 +134,7 @@ void WeakProcessor::weak_oops_do(WorkGang* workers,
                                  WeakProcessorPhaseTimes* phase_times) {
   WeakProcessorTimeTracker tt(phase_times);
 
-  uint nworkers = ergo_workers(MIN2(workers->active_workers(),
+  uint nworkers = ergo_workers(MIN2(workers->total_workers(),
                                     phase_times->max_threads()));
 
   GangTask task("Weak Processor", is_alive, keep_alive, phase_times, nworkers);
@@ -147,7 +147,7 @@ void WeakProcessor::weak_oops_do(WorkGang* workers,
                                  IsAlive* is_alive,
                                  KeepAlive* keep_alive,
                                  uint indent_log) {
-  uint nworkers = ergo_workers(workers->active_workers());
+  uint nworkers = ergo_workers(workers->total_workers());
   WeakProcessorPhaseTimes pt(nworkers);
   weak_oops_do(workers, is_alive, keep_alive, &pt);
   pt.log_print_phases(indent_log);