--- a/hotspot/src/share/vm/gc/g1/g1ConcurrentMark.cpp	Tue Sep 06 22:52:35 2016 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1ConcurrentMark.cpp	Wed Sep 07 09:20:10 2016 +0200
@@ -1035,6 +1035,8 @@
   // worker threads may currently exist and more may not be
   // available.
   active_workers = _parallel_workers->update_active_workers(active_workers);
+  log_info(gc, task)("Using %u workers of %u for marking", active_workers, _parallel_workers->total_workers());
+
   // Parallel task terminator is set in "set_concurrency_and_phase()"
   set_concurrency_and_phase(active_workers, true /* concurrent */);