run_config = tf.contrib.tpu.RunConfig(
        cluster=tpu_cluster_resolver,
        master=FLAGS.master,
        model_dir=FLAGS.output_dir,
        save_checkpoints_steps=FLAGS.save_checkpoints_steps,
        tpu_config=tf.contrib.tpu.TPUConfig(
                iterations_per_loop=FLAGS.iterations_per_loop,
                num_shards=FLAGS.num_tpu_cores,
                per_host_input_for_training=is_per_host))