message: Set context.MIRRORING_ALL by default in TPUStrategy, this is to make sure TPU Pod gets good performance in TF2.0.
diff: @@ -87,6 +87,10 @@ def initialize_tpu_system(cluster_resolver=None):
  context.context()._clear_caches() # pylint: disable=protected-access
  serialized_topology = output.numpy()
  +
  + # TODO(b/134094971): Remove this when lazy tensor copy in multi-device
  + # function has been implemented.
  + context.context().mirroring_policy = context.MIRRORING_ALL
  else:
  master = cluster_resolver.master()
  cluster_spec = cluster_resolver.cluster_spec()
  