src/share/vm/gc/g1/g1CollectedHeap.cpp

rev 10739 : 8153745: Avoid spawning G1ParPreserveCMReferentsTask when there is no work to be done
Reviewed-by:

*** 4438,4448 ****
    double ref_proc_time = os::elapsedTime() - ref_proc_start;
    g1_policy()->phase_times()->record_ref_proc_time(ref_proc_time * 1000.0);
  }
  
  void G1CollectedHeap::preserve_cm_referents(G1ParScanThreadStateSet* per_thread_states) {
-   double preserve_cm_referents_start = os::elapsedTime();
    // Any reference objects, in the collection set, that were 'discovered'
    // by the CM ref processor should have already been copied (either by
    // applying the external root copy closure to the discovered lists, or
    // by following an RSet entry).
    //
--- 4438,4447 ----
*** 4459,4478 ****
    //
    // We also need to do this copying before we process the reference
    // objects discovered by the STW ref processor in case one of these
    // referents points to another object which is also referenced by an
    // object discovered by the STW ref processor.
  
    uint no_of_gc_workers = workers()->active_workers();
- 
    G1ParPreserveCMReferentsTask keep_cm_referents(this,
                                                   per_thread_states,
                                                   no_of_gc_workers,
                                                   _task_queues);
    workers()->run_task(&keep_cm_referents);
  
!   g1_policy()->phase_times()->record_preserve_cm_referents_time_ms((os::elapsedTime() - preserve_cm_referents_start) * 1000.0);
  }
  
  // Weak Reference processing during an evacuation pause (part 1).
  void G1CollectedHeap::process_discovered_references(G1ParScanThreadStateSet* per_thread_states) {
    double ref_proc_start = os::elapsedTime();
--- 4458,4481 ----
    //
    // We also need to do this copying before we process the reference
    // objects discovered by the STW ref processor in case one of these
    // referents points to another object which is also referenced by an
    // object discovered by the STW ref processor.
+   double preserve_cm_referents_time = 0.0;
  
+   if (_ref_processor_cm->has_discovered_references()) {
+     double preserve_cm_referents_start = os::elapsedTime();
      uint no_of_gc_workers = workers()->active_workers();
      G1ParPreserveCMReferentsTask keep_cm_referents(this,
                                                     per_thread_states,
                                                     no_of_gc_workers,
                                                     _task_queues);
      workers()->run_task(&keep_cm_referents);
+     preserve_cm_referents_time = os::elapsedTime() - preserve_cm_referents_start;
+   }
  
!   g1_policy()->phase_times()->record_preserve_cm_referents_time_ms(preserve_cm_referents_time * 1000.0);
  }
  
  // Weak Reference processing during an evacuation pause (part 1).
  void G1CollectedHeap::process_discovered_references(G1ParScanThreadStateSet* per_thread_states) {
    double ref_proc_start = os::elapsedTime();