Example #1
0
  def testDense(self, units, use_bias):
    batch = 2
    channels = 3
    inputs = tf.random_normal([batch, channels])

    graph = mtf.Graph()
    mesh = mtf.Mesh(graph, "my_mesh")
    batch_dim = mtf.Dimension("batch", batch)
    channels_dim = mtf.Dimension("channels", channels)
    depth_dim = mtf.Dimension("depth", units)

    mtf_inputs = mtf.import_tf_tensor(
        mesh, inputs, shape=mtf.Shape([batch_dim, channels_dim]))
    mtf_outputs = mtf_layers.dense(mtf_inputs,
                                   output_dim=depth_dim,
                                   reduced_dims=[channels_dim],
                                   activation=mtf.relu,
                                   use_bias=use_bias)
    mesh_impl = placement_mesh_impl.PlacementMeshImpl(
        shape=[], layout={}, devices=[""])
    lowering = mtf.Lowering(graph, {mesh: mesh_impl})
    actual_outputs = lowering.export_to_tf_tensor(mtf_outputs)

    expected_outputs = tf.keras.layers.Dense(units=units,
                                             activation=tf.nn.relu,
                                             use_bias=use_bias)(inputs)
    tf_group = lowering.copy_masters_to_slices()
    init = tf.global_variables_initializer()
    with self.test_session() as sess:
      sess.run(init)
      sess.run(tf_group)
      actual, expected = sess.run([actual_outputs, expected_outputs])

    self.assertEqual(actual.shape, expected.shape)
Example #2
0
 def estimator_spec_predict(self, features, mesh, mesh_impl, use_tpu):
     mtf_samples = self.sample(features, mesh)
     lowering = mtf.Lowering(mesh.graph, {mesh: mesh_impl})
     outputs = lowering.export_to_tf_tensor(mtf_samples)
     if self.has_input:
         ndims = len(outputs.shape.as_list())
         actual_batch_size = tf.shape(features["inputs"])[0]
         outputs = tf.slice(outputs, [0] * ndims,
                            [actual_batch_size] + [-1] * (ndims - 1))
     predictions = {
         "outputs": outputs,
         "targets": features.get("infer_targets", features.get("inputs")),
         "inputs": features.get("inputs"),
     }
     if use_tpu:
         _remove_summaries()
         return tpu_estimator.TPUEstimatorSpec(
             mode=tf.estimator.ModeKeys.PREDICT,
             predictions=predictions,
             prediction_hooks=[mtf.MtfRestoreHook(lowering)])
     else:
         return tf.estimator.EstimatorSpec(
             tf.estimator.ModeKeys.PREDICT,
             predictions=predictions,
             prediction_hooks=[mtf.MtfRestoreHook(lowering)])
Example #3
0
  def testLayerNorm(self):
    batch = 2
    channels = 3
    inputs = tf.random_normal([batch, channels])

    graph = mtf.Graph()
    mesh = mtf.Mesh(graph, "my_mesh")
    batch_dim = mtf.Dimension("batch", batch)
    channels_dim = mtf.Dimension("channels", channels)

    mtf_inputs = mtf.import_tf_tensor(
        mesh, inputs, shape=mtf.Shape([batch_dim, channels_dim]))
    mtf_outputs = mtf_layers.layer_norm(mtf_inputs,
                                        dim=channels_dim)
    mesh_impl = placement_mesh_impl.PlacementMeshImpl(
        shape=[], layout={}, devices=[""])
    lowering = mtf.Lowering(graph, {mesh: mesh_impl})
    actual_outputs = lowering.export_to_tf_tensor(mtf_outputs)

    expected_outputs = common_layers.layer_norm(inputs)
    tf_group = lowering.copy_masters_to_slices()
    init = tf.global_variables_initializer()
    with self.test_session() as sess:
      sess.run(init)
      sess.run(tf_group)
      actual, expected = sess.run([actual_outputs, expected_outputs])

    self.assertEqual(actual.shape, expected.shape)
Example #4
0
    def testWeightsNonzero(self):
        inputs = tf.constant([[3, 1, 0], [1, 0, 0]])

        graph = mtf.Graph()
        mesh = mtf.Mesh(graph, "my_mesh")
        batch_dim = mtf.Dimension("batch", inputs.shape.as_list()[0])
        channels_dim = mtf.Dimension("channels", inputs.shape.as_list()[1])

        mtf_inputs = mtf.import_tf_tensor(mesh,
                                          inputs,
                                          shape=mtf.Shape(
                                              [batch_dim, channels_dim]))
        mtf_outputs = mtf_layers.weights_nonzero(mtf_inputs)
        mesh_impl = placement_mesh_impl.PlacementMeshImpl(shape=[],
                                                          layout={},
                                                          devices=[""])
        lowering = mtf.Lowering(graph, {mesh: mesh_impl})
        actual_outputs = lowering.export_to_tf_tensor(mtf_outputs)

        expected_outputs = common_layers.weights_nonzero(inputs)
        tf_group = lowering.copy_masters_to_slices()
        self.evaluate(tf_group)
        actual, expected = self.evaluate([actual_outputs, expected_outputs])

        self.assertAllEqual(actual, expected)
Example #5
0
  def testDenseReluDense(self):
    batch = 2
    channels = 3
    hidden = 5
    inputs = tf.random_normal([batch, channels])

    graph = mtf.Graph()
    mesh = mtf.Mesh(graph, "my_mesh")
    batch_dim = mtf.Dimension("batch", batch)
    channels_dim = mtf.Dimension("channels", channels)
    hidden_dim = mtf.Dimension("hidden", hidden)

    mtf_inputs = mtf.import_tf_tensor(
        mesh, inputs, shape=mtf.Shape([batch_dim, channels_dim]))
    mtf_outputs = mtf_layers.dense_relu_dense(mtf_inputs,
                                              hidden_channels=hidden_dim)
    mesh_impl = placement_mesh_impl.PlacementMeshImpl(
        shape=[], layout={}, devices=[""])
    lowering = mtf.Lowering(graph, {mesh: mesh_impl})
    actual_outputs = lowering.export_to_tf_tensor(mtf_outputs)

    tf_group = lowering.copy_masters_to_slices()
    init = tf.global_variables_initializer()
    with self.test_session() as sess:
      sess.run(init)
      sess.run(tf_group)
      actual = sess.run(actual_outputs)

    self.assertEqual(actual.shape, inputs.shape)
Example #6
0
    def testDotProductAttention(self, batch, heads, length_q, length_kv,
                                depth_k, depth_v):
        query = tf.random_normal([batch, heads, length_q, depth_k])
        key = tf.random_normal([batch, heads, length_kv, depth_k])
        value = tf.random_normal([batch, heads, length_kv, depth_v])

        graph = mtf.Graph()
        mesh = mtf.Mesh(graph, "my_mesh")
        batch_dim = mtf.Dimension("batch", batch)
        heads_dim = mtf.Dimension("heads", heads)
        length_q_dim = mtf.Dimension("length_q", length_q)
        length_kv_dim = mtf.Dimension("length_kv", length_kv)
        depth_k_dim = mtf.Dimension("depth_k", depth_k)
        depth_v_dim = mtf.Dimension("depth_v", depth_v)

        mtf_query = mtf.import_tf_tensor(
            mesh,
            query,
            shape=mtf.Shape([batch_dim, heads_dim, length_q_dim, depth_k_dim]))
        mtf_key = mtf.import_tf_tensor(
            mesh,
            key,
            shape=mtf.Shape([batch_dim, heads_dim, length_kv_dim,
                             depth_k_dim]))
        mtf_value = mtf.import_tf_tensor(
            mesh,
            value,
            shape=mtf.Shape([batch_dim, heads_dim, length_kv_dim,
                             depth_v_dim]))
        mtf_outputs = mtf_layers.dot_product_attention(mtf_query,
                                                       mtf_key,
                                                       mtf_value,
                                                       mask=None)
        mesh_impl = placement_mesh_impl.PlacementMeshImpl(shape=[],
                                                          layout={},
                                                          devices=[""])
        lowering = mtf.Lowering(graph, {mesh: mesh_impl})
        actual_outputs = lowering.export_to_tf_tensor(mtf_outputs)

        tf_group = lowering.copy_masters_to_slices()
        init = tf.global_variables_initializer()
        with self.test_session() as sess:
            sess.run(init)
            sess.run(tf_group)
            actual = sess.run(actual_outputs)

        self.assertEqual(actual.shape, (batch, heads, length_q, depth_v))
Example #7
0
    def testMtfTransformerDataParallel(self):
        hparams = mtf_transformer.mtf_transformer_single()

        model, features, hparams = get_model(hparams)
        hparams.mesh_shape = "all:2"
        hparams.layout = "batch:all"
        mesh, mesh_impl = get_placement_mesh(hparams)

        logits, _ = model.mtf_model_fn(features, mesh)
        lowering = mtf.Lowering(mesh.graph, {mesh: mesh_impl})
        tf_group = lowering.copy_masters_to_slices()
        tf_logits = lowering.export_to_tf_tensor(logits)

        with self.test_session() as session:
            session.run(tf.global_variables_initializer())
            session.run(tf_group)
            res = session.run(tf_logits)
        self.assertEqual(res.shape, (BATCH_SIZE, TARGET_LENGTH, VOCAB_SIZE))
  def testLowering(self):
    graph = mtf.Graph()
    mesh = mtf.Mesh(graph, "my_mesh")
    inputs = tf.constant(0.)
    mtf_inputs = mtf.import_tf_tensor(mesh,
                                      tf_tensor=inputs,
                                      shape=mtf.Shape([]))
    mesh_impl = placement_mesh_impl.PlacementMeshImpl(
        shape=[], layout={}, devices=[""])
    lowering = mtf.Lowering(graph, {mesh: mesh_impl})

    outputs = lowering.export_to_tf_tensor(mtf_inputs)
    inputs_value, outputs_value = self.evaluate([inputs, outputs])
    self.assertEqual(inputs_value, outputs_value)

    # Check that methods run without error.
    _ = lowering.copy_masters_to_slices()
    _ = lowering.copy_slices_to_masters()
Example #9
0
    def testMaskedLocalAttention1D(self, batch, length, io_channels,
                                   kv_channels, heads, block_length):
        length_q = length
        length_m = length
        query = tf.random_normal([batch, length_q, io_channels])
        memory = tf.random_normal([batch, length_m, io_channels])

        graph = mtf.Graph()
        mesh = mtf.Mesh(graph, "my_mesh")
        batch_dim = mtf.Dimension("batch", batch)
        length_q_dim = mtf.Dimension("length_q", length_q)
        length_m_dim = mtf.Dimension("length_m", length_m)
        io_channels_dim = mtf.Dimension("io_channels", io_channels)
        kv_channels_dim = mtf.Dimension("kv_channels", kv_channels)
        heads_dim = mtf.Dimension("heads", heads)

        mtf_query = mtf.import_tf_tensor(
            mesh,
            query,
            shape=mtf.Shape([batch_dim, length_q_dim, io_channels_dim]))
        mtf_memory = mtf.import_tf_tensor(
            mesh,
            memory,
            shape=mtf.Shape([batch_dim, length_m_dim, io_channels_dim]))
        mtf_outputs = mtf_layers.masked_local_attention_1d(
            mtf_query,
            mtf_memory,
            kv_channels=kv_channels_dim,
            heads=heads_dim,
            block_length=block_length)
        mesh_impl = placement_mesh_impl.PlacementMeshImpl(shape=[],
                                                          layout={},
                                                          devices=[""])
        lowering = mtf.Lowering(graph, {mesh: mesh_impl})
        actual_outputs = lowering.export_to_tf_tensor(mtf_outputs)

        tf_group = lowering.copy_masters_to_slices()
        init = tf.global_variables_initializer()
        with self.test_session() as sess:
            sess.run(init)
            sess.run(tf_group)
            actual = sess.run(actual_outputs)

        self.assertEqual(actual.shape, (batch, length_q, io_channels))
    def testMtfImageTransformer(self):
        hparams = mtf_image_transformer.mtf_image_transformer_single()

        model, features, hparams = get_model(hparams)
        hparams.mesh_shape = ""
        hparams.layout = ""
        mesh, mesh_impl = get_placement_mesh(hparams)

        logits, _ = model.mtf_model_fn(features, mesh)
        lowering = mtf.Lowering(mesh.graph, {mesh: mesh_impl})
        tf_group = lowering.copy_masters_to_slices()
        tf_logits = lowering.outfeed(logits)

        with self.test_session() as session:
            session.run(tf.global_variables_initializer())
            session.run(tf_group)
            res = session.run(tf_logits)
        self.assertEqual(res.shape,
                         (BATCH_SIZE, IMG_LENGTH * IMG_LENGTH, VOCAB_SIZE))
Example #11
0
    def testMultiheadAttention(self, kv_channels, heads):
        batch = 2
        length = 8
        channels = 3
        query = tf.random_normal([batch, length, channels])

        graph = mtf.Graph()
        mesh = mtf.Mesh(graph, "my_mesh")
        batch_dim = mtf.Dimension("batch", batch)
        length_dim = mtf.Dimension("length", length)
        channels_dim = mtf.Dimension("channels", channels)
        kv_channels_dim = mtf.Dimension("kv_channels", kv_channels)
        heads_dim = mtf.Dimension("heads", heads)

        mtf_query = mtf.import_tf_tensor(
            mesh,
            query,
            shape=mtf.Shape([batch_dim, length_dim, channels_dim]))
        mtf_outputs = mtf_layers.multihead_attention(
            mtf_query,
            memory_antecedent=None,
            mask=None,
            kv_channels=kv_channels_dim,
            heads=heads_dim)
        mesh_impl = placement_mesh_impl.PlacementMeshImpl(shape=[],
                                                          layout={},
                                                          devices=[""])
        lowering = mtf.Lowering(graph, {mesh: mesh_impl})
        actual_outputs = lowering.export_to_tf_tensor(mtf_outputs)

        tf_group = lowering.copy_masters_to_slices()
        init = tf.global_variables_initializer()
        with self.test_session() as sess:
            sess.run(init)
            sess.run(tf_group)
            actual = sess.run(actual_outputs)

        self.assertEqual(actual.shape, query.shape)
Example #12
0
    def estimator_model_fn(cls,
                           hparams,
                           features,
                           labels,
                           mode,
                           config=None,
                           params=None,
                           decode_hparams=None,
                           use_tpu=False,
                           xla_compile=False):
        del xla_compile
        hparams = copy.deepcopy(hparams)
        hparams.use_tpu = use_tpu
        # merge decode_hparams into hparams if present
        if mode == tf.estimator.ModeKeys.PREDICT and decode_hparams is not None:
            for k, v in six.iteritems(decode_hparams.values()):
                if hasattr(hparams, k) and getattr(hparams, k) != v:
                    tf.logging.warning(
                        "Overriding hparams.%s with %s from decode_hparams" %
                        (k, v))
                setattr(hparams, k, v)

        # Instantiate model
        data_parallelism = None
        if not use_tpu and config:
            data_parallelism = config.data_parallelism
        model = cls(hparams,
                    mode,
                    data_parallelism=data_parallelism,
                    decode_hparams=decode_hparams)

        global_step = tf.train.get_global_step()
        graph = mtf.Graph()
        mesh = mtf.Mesh(graph, "my_mesh")

        mesh_shape = mtf.convert_to_shape(hparams.mesh_shape)
        layout_rules = mtf.convert_to_layout_rules(hparams.layout)
        if use_tpu:
            mesh_devices = [""] * mesh_shape.size
            mesh_impl = simd_mesh_impl.SimdMeshImpl(
                mesh_shape, layout_rules, mesh_devices,
                params["context"].device_assignment)
        else:
            if len(data_parallelism.ps_devices) == 1:
                mesh_devices = [""] * mesh_shape.size
            else:
                assert len(data_parallelism.ps_devices) == mesh_shape.size
                mesh_devices = data_parallelism.ps_devices
            mesh_impl = placement_mesh_impl.PlacementMeshImpl(
                mesh_shape, layout_rules, mesh_devices)

        # PREDICT mode
        if mode == tf.estimator.ModeKeys.PREDICT:
            return model.estimator_spec_predict(features, mesh, mesh_impl,
                                                use_tpu)

        logits, loss = model.mtf_model_fn(features, mesh)
        if use_tpu and logits is not None:
            logits = mtf.anonymize(logits)

        # TRAIN mode
        if mode == tf.estimator.ModeKeys.TRAIN:
            var_grads = mtf.gradients(
                [loss], [v.outputs[0] for v in graph.trainable_variables])
            lr = learning_rate.learning_rate_schedule(hparams)
            mtf_lr = mtf.import_tf_tensor(
                mesh, tf.convert_to_tensor(lr, dtype=tf.float32),
                mtf.Shape([]))
            optimizer = mtf_optimize.make_optimizer(hparams, mtf_lr)
            update_ops = []
            for grad, var in zip(var_grads, graph.trainable_variables):
                update_ops.extend(optimizer.apply_grad(grad, var))

        lowering = mtf.Lowering(graph, {mesh: mesh_impl})

        tf_loss = lowering.export_to_tf_tensor(loss)
        tf_loss = tf.to_float(tf_loss)
        if logits and mode != tf.estimator.ModeKeys.TRAIN:
            tf_logits = lowering.export_to_tf_tensor(logits)

        if mode == tf.estimator.ModeKeys.TRAIN:
            tf_update_ops = [
                lowering.lowered_operation(op) for op in update_ops
            ]
            tf_update_ops.append(tf.assign_add(global_step, 1))
            # tf.logging.info("tf_update_ops: {}".format(tf_update_ops))
            train_op = tf.group(tf_update_ops)

        with mtf_utils.outside_all_rewrites():
            # Copy master variables to slices. Must be called first.
            restore_hook = mtf.MtfRestoreHook(lowering)
            saver = tf.train.Saver(tf.global_variables(),
                                   sharded=True,
                                   max_to_keep=10,
                                   keep_checkpoint_every_n_hours=2,
                                   defer_build=False,
                                   save_relative_paths=True)
            tf.add_to_collection(tf.GraphKeys.SAVERS, saver)
            saver_listener = mtf.MtfCheckpointSaverListener(lowering)
            saver_hook = tf.train.CheckpointSaverHook(
                hparams.model_dir,
                save_steps=1000,
                saver=saver,
                listeners=[saver_listener])

        # EVAL mode
        if mode == tf.estimator.ModeKeys.EVAL:
            tf_logits = lowering.export_to_tf_tensor(logits)
            return model.estimator_spec_eval(features, tf_logits, labels,
                                             tf_loss, restore_hook, use_tpu)

        if use_tpu:
            _remove_summaries()
            return tpu_estimator.TPUEstimatorSpec(
                mode=tf.estimator.ModeKeys.TRAIN,
                loss=tf_loss,
                train_op=train_op,
                training_hooks=[restore_hook, saver_hook])
        else:
            return tf.estimator.EstimatorSpec(
                tf.estimator.ModeKeys.TRAIN,
                loss=tf_loss,
                train_op=train_op,
                training_chief_hooks=[restore_hook, saver_hook])
Example #13
0
def model_fn(features, labels, mode, params):
    """The model_fn argument for creating an Estimator."""
    tf.logging.info("features = %s labels = %s mode = %s params=%s" %
                    (features, labels, mode, params))
    global_step = tf.train.get_global_step()
    graph = mtf.Graph()
    mesh = mtf.Mesh(graph, "my_mesh")
    logits, loss = mnist_model(features, labels, mesh)
    mesh_shape = mtf.parse_mesh_shape(FLAGS.mesh_shape)
    mesh_size = mtf.list_product(mesh_shape)
    mesh_devices = [""] * mesh_size
    mesh_impl = placement_mesh_impl.PlacementMeshImpl(
        mesh_shape, mtf.parse_layout(FLAGS.layout), mesh_devices)

    if mode == tf.estimator.ModeKeys.TRAIN:
        var_grads = mtf.gradients(
            [loss], [v.outputs[0] for v in graph.trainable_variables])
        optimizer = mtf_optimize.AdafactorOptimizer()
        update_ops = []
        for grad, var in zip(var_grads, graph.trainable_variables):
            update_ops.extend(optimizer.apply_grad(grad, var))

    lowering = mtf.Lowering(graph, {mesh: mesh_impl})
    restore_hook = mtf.MtfRestoreHook(lowering)

    tf_logits = lowering.outfeed(logits)
    if mode != tf.estimator.ModeKeys.PREDICT:
        tf_loss = lowering.outfeed(loss)
        tf.summary.scalar("loss", tf_loss)

    if mode == tf.estimator.ModeKeys.TRAIN:
        tf_update_ops = [lowering.lowered_operation(op) for op in update_ops]
        tf_update_ops.append(tf.assign_add(global_step, 1))
        train_op = tf.group(tf_update_ops)
        saver = tf.train.Saver(tf.global_variables(),
                               sharded=True,
                               max_to_keep=10,
                               keep_checkpoint_every_n_hours=2,
                               defer_build=False,
                               save_relative_paths=True)
        tf.add_to_collection(tf.GraphKeys.SAVERS, saver)
        saver_listener = mtf.MtfCheckpointSaverListener(lowering)
        saver_hook = tf.train.CheckpointSaverHook(FLAGS.model_dir,
                                                  save_steps=1000,
                                                  saver=saver,
                                                  listeners=[saver_listener])

        accuracy = tf.metrics.accuracy(labels=labels,
                                       predictions=tf.argmax(tf_logits,
                                                             axis=1))

        # Name tensors to be logged with LoggingTensorHook.
        tf.identity(tf_loss, "cross_entropy")
        tf.identity(accuracy[1], name="train_accuracy")

        # Save accuracy scalar to Tensorboard output.
        tf.summary.scalar("train_accuracy", accuracy[1])

        # restore_hook must come before saver_hook
        return tf.estimator.EstimatorSpec(
            tf.estimator.ModeKeys.TRAIN,
            loss=tf_loss,
            train_op=train_op,
            training_chief_hooks=[restore_hook, saver_hook])

    if mode == tf.estimator.ModeKeys.PREDICT:
        predictions = {
            "classes": tf.argmax(tf_logits, axis=1),
            "probabilities": tf.nn.softmax(tf_logits),
        }
        return tf.estimator.EstimatorSpec(
            mode=tf.estimator.ModeKeys.PREDICT,
            predictions=predictions,
            prediction_hooks=[restore_hook],
            export_outputs={
                "classify": tf.estimator.export.PredictOutput(predictions)
            })
    if mode == tf.estimator.ModeKeys.EVAL:
        return tf.estimator.EstimatorSpec(
            mode=tf.estimator.ModeKeys.EVAL,
            loss=tf_loss,
            evaluation_hooks=[restore_hook],
            eval_metric_ops={
                "accuracy":
                tf.metrics.accuracy(labels=labels,
                                    predictions=tf.argmax(tf_logits, axis=1)),
            })
def model_fn(features, labels, mode, params):
  """A model is called by TpuEstimator."""
  del labels
  global_step = tf.train.get_global_step()
  graph = mtf.Graph()
  mesh = mtf.Mesh(graph, 'my_mesh')
  mesh_shape = mtf.convert_to_shape(FLAGS.mesh_shape)
  mesh_devices = [''] * mesh_shape.size
  mesh_impl = SimdMeshImpl(
      mesh_shape, mtf.convert_to_layout_rules(FLAGS.layout),
      mesh_devices, params['context'].device_assignment)
  with mtf_utils.outside_all_rewrites():
    logits, loss = toy_model(features, mesh)

  # TRAIN mode
  if mode == tf.estimator.ModeKeys.TRAIN:
    var_grads = mtf.gradients([loss],
                              [v.outputs[0] for v in graph.trainable_variables])
    optimizer = mtf_optimize.AdafactorOptimizer()
    update_ops = []
    for grad, var in zip(var_grads, graph.trainable_variables):
      update_ops.extend(optimizer.apply_grad(grad, var))
  else:
    # for now, we can only export fully-replicated tensors.
    fully_replicated_logits = mtf.anonymize(logits)

  lowering = mtf.Lowering(graph, {mesh: mesh_impl})

  tf_loss = lowering.export_to_tf_tensor(loss)

  if mode == tf.estimator.ModeKeys.TRAIN:
    tf_update_ops = [lowering.lowered_operation(op) for op in update_ops]
    tf_update_ops.append(tf.assign_add(global_step, 1))
    tf.logging.info('tf_update_ops: {}'.format(tf_update_ops))
    train_op = tf.group(tf_update_ops)
  else:
    tf_logits = lowering.export_to_tf_tensor(fully_replicated_logits)

  with mtf_utils.outside_all_rewrites():
    # Copy master variables to slices. Must be called first.
    restore_hook = mtf.MtfRestoreHook(lowering)
    if mode == tf.estimator.ModeKeys.TRAIN:
      saver = tf.train.Saver(
          tf.global_variables(),
          sharded=True,
          max_to_keep=10,
          keep_checkpoint_every_n_hours=2,
          defer_build=False,
          save_relative_paths=True)
      tf.add_to_collection(tf.GraphKeys.SAVERS, saver)
      saver_listener = mtf.MtfCheckpointSaverListener(lowering)
      saver_hook = tf.train.CheckpointSaverHook(
          FLAGS.model_dir,
          save_steps=1000,
          saver=saver,
          listeners=[saver_listener])

      return tpu_estimator.TPUEstimatorSpec(
          tf.estimator.ModeKeys.TRAIN,
          loss=tf_loss,
          train_op=train_op,
          training_hooks=[restore_hook, saver_hook])
    elif mode == tf.estimator.ModeKeys.EVAL:

      def metric_fn(tf_logits):
        mean_logitss = tf.metrics.mean(tf_logits)
        return {'mean_logitss': mean_logitss}

      eval_metrics = (metric_fn, [tf_logits])

      return tpu_estimator.TPUEstimatorSpec(
          tf.estimator.ModeKeys.EVAL,
          evaluation_hooks=[restore_hook],
          loss=tf_loss,
          eval_metrics=eval_metrics)