--- /dev/null	2018-04-03 12:55:20.301839954 +0200
+++ new/src/hotspot/share/gc/z/zWorkers.cpp	2018-06-08 19:46:49.771003795 +0200
@@ -0,0 +1,133 @@
+/*
+ * Copyright (c) 2015, 2017, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include "precompiled.hpp"
+#include "gc/z/zTask.hpp"
+#include "gc/z/zWorkers.inline.hpp"
+#include "runtime/os.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/safepoint.hpp"
+
+uint ZWorkers::calculate_ncpus(double share_in_percent) {
+  return ceil(os::initial_active_processor_count() * share_in_percent / 100.0);
+}
+
+uint ZWorkers::calculate_nparallel() {
+  // Use 60% of the CPUs, rounded up. We would like to use as many threads as
+  // possible to increase parallelism. However, using a thread count that is
+  // close to the number of processors tends to lead to over-provisioning and
+  // scheduling latency issues. Using 60% of the active processors appears to
+  // be a fairly good balance.
+  return calculate_ncpus(60.0);
+}
+
+uint ZWorkers::calculate_nconcurrent() {
+  // Use 12.5% of the CPUs, rounded up. The number of concurrent threads we
+  // would like to use heavily depends on the type of workload we are running.
+  // Using too many threads will have a nagative impact on the application
+  // throughput, while using too few threads will prolong the GC-cycle and
+  // we then risk being out-run by the application. Using 12.5% of the active
+  // processors appears to be a fairly good balance.
+  return calculate_ncpus(12.5);
+}
+
+class ZWorkersWarmupTask : public ZTask {
+private:
+  const uint _nworkers;
+  uint       _started;
+  Monitor    _monitor;
+
+public:
+  ZWorkersWarmupTask(uint nworkers) :
+      ZTask("ZWorkersWarmupTask"),
+      _nworkers(nworkers),
+      _started(0),
+      _monitor(Monitor::leaf, "ZWorkersWarmup", false, Monitor::_safepoint_check_never) {}
+
+  virtual void work() {
+    // Wait for all threads to start
+    MonitorLockerEx ml(&_monitor, Monitor::_no_safepoint_check_flag);
+    if (++_started == _nworkers) {
+      // All threads started
+      ml.notify_all();
+    } else {
+      while (_started != _nworkers) {
+        ml.wait(Monitor::_no_safepoint_check_flag);
+      }
+    }
+  }
+};
+
+ZWorkers::ZWorkers() :
+    _boost(false),
+    _workers("ZWorker",
+             nworkers(),
+             true /* are_GC_task_threads */,
+             true /* are_ConcurrentGC_threads */) {
+
+  log_info(gc, init)("Workers: %u parallel, %u concurrent", nparallel(), nconcurrent());
+
+  // Initialize worker threads
+  _workers.initialize_workers();
+  _workers.update_active_workers(nworkers());
+  if (_workers.active_workers() != nworkers()) {
+    vm_exit_during_initialization("Failed to create ZWorkers");
+  }
+
+  // Warm up worker threads by having them execute a dummy task.
+  // This helps reduce latency in early GC pauses, which otherwise
+  // would have to take on any warmup costs.
+  ZWorkersWarmupTask task(nworkers());
+  run(&task, nworkers());
+}
+
+void ZWorkers::set_boost(bool boost) {
+  if (boost) {
+    log_debug(gc)("Boosting workers");
+  }
+
+  _boost = boost;
+}
+
+void ZWorkers::run(ZTask* task, uint nworkers) {
+  log_debug(gc, task)("Executing Task: %s, Active Workers: %u", task->name(), nworkers);
+  _workers.update_active_workers(nworkers);
+  _workers.run_task(task->gang_task());
+}
+
+void ZWorkers::run_parallel(ZTask* task) {
+  assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
+  run(task, nparallel());
+}
+
+void ZWorkers::run_concurrent(ZTask* task) {
+  run(task, nconcurrent());
+}
+
+void ZWorkers::threads_do(ThreadClosure* tc) const {
+  _workers.threads_do(tc);
+}
+
+void ZWorkers::print_threads_on(outputStream* st) const {
+  _workers.print_worker_threads_on(st);
+}