import tensorflow as tf

            mask loss.
          learning_rate: `Tensor` with shape `[batch, ]` for the learning_rate.

        Returns:
          List of summary ops to run on the CPU host.
        """
        # Outfeed supports int32 but global_step is expected to be int64.
        global_step = tf.reduce_mean(global_step)
        # Host call fns are executed FLAGS.iterations_per_loop times after one
        # TPU loop is finished, setting max_queue value to the same as number of
        # iterations will make the summary writer only flush the data to storage
        # once per loop.
        with (tf.contrib.summary.create_file_writer(
            params['model_dir'],
