message: Comment on why NCCL can't be ordered in tf1.
diff: @@ -286,6 +286,8 @@ class CollectiveReplicaLauncher(object):
  return CollectiveReplicaLauncher._prefer_unique_instance_key
  def _use_ordering_token(self):
  + # We rely on auto control dep to insert control edges between NCCL calls,
  + # but for tf1 graph mode auto control dep is not used.
  if not ops.executing_eagerly_outside_functions():
  return False
  return CollectiveReplicaLauncher._prefer_ordering_token
  