tf.distribute.experimental.TPUStrategy

Synchronous training on TPUs and TPU Pods.

Inherits From: Strategy

To construct a TPUStrategy object, you need to run the initialization code as below:

resolver = tf.distribute.cluster_resolver.TPUClusterResolver(tpu='')
tf.config.experimental_connect_to_cluster(resolver)
tf.tpu.experimental.initialize_tpu_system(resolver)
strategy = tf.distribute.experimental.TPUStrategy(resolver)

While using distribution strategies, the variables created within the strategy's scope will be replicated across all the replicas and can be kept in sync using all-reduce algorithms.

To run TF2 programs on TPUs, you can either use .compile and .fit APIs in tf.keras with TPUStrategy, or write your own customized training loop by calling strategy.run directly. Note that TPUStrategy doesn't support pure eager execution, so please make sure the function passed into strategy.run is a tf.function or strategy.run is called inside a tf.function if eager behavior is enabled.

tpu_cluster_resolver A tf.distribute.cluster_resolver.TPUClusterResolver, which provides information about the TPU cluster.
device_assignment Optional tf.tpu.experimental.DeviceAssignment to specify the placement of replicas on the TPU cluster.

cluster_resolver Returns the cluster resolver associated with this strategy.

tf.distribute.experimental.TPUStrategy provides the associated tf.distribute.cluster_resolver.ClusterResolver. If the user provides one in __init__, that instance is returned; if the user does not, a default tf.distribute.cluster_resolver.TPUClusterResolver is provided.

extended tf.distribute.StrategyExtended with additional methods.
num_replicas_in_sync Returns number of replicas over which gradients are aggregated.

Methods

experimental_assign_to_logical_device

View source

Adds annotation that tensor will be assigned to a logical device.


# Initializing TPU system with 2 logical devices and 4 replicas.
resolver = tf.distribute.cluster_resolver.TPUClusterResolver(tpu='')
tf.config.experimental_connect_to_cluster(resolver)
topology = tf.tpu.experimental.initialize_tpu_system(resolver)
device_assignment = tf.tpu.experimental.DeviceAssignment.build(
    topology,
    computation_shape=[1, 1, 1, 2],
    num_replicas=4)
strategy = tf.distribute.TPUStrategy(
    resolver, experimental_device_assignment=device_assignment)
iterator = iter(inputs)

@tf.function()
def step_fn(inputs):
  output = tf.add(inputs, inputs)

  # Add operation will be executed on logical device 0.
  output = strategy.experimental_assign_to_logical_device(output, 0)
  return output

strategy.run(step_fn, args=(next(iterator),))

Args
tensor Input tensor to annotate.
logical_device_id Id of the logical core to which the tensor will be assigned.

Raises
ValueError The logical device id presented is not consistent with total number of partitions specified by the device assignment.

Returns
Annotated tensor with idential value as tensor.

experimental_distribute_dataset

View source