tf.compat.v1.distribute.experimental.MultiWorkerMirroredStrategy

A distribution strategy for synchronous training on multiple workers.

Inherits From: Strategy

tf.compat.v1.distribute.experimental.MultiWorkerMirroredStrategy(
    communication=tf.distribute.experimental.CollectiveCommunication.AUTO,
    cluster_resolver=None
)

This strategy implements synchronous distributed training across multiple workers, each with potentially multiple GPUs. Similar to tf.distribute.MirroredStrategy, it creates copies of all variables in the model on each device across all workers.

It uses CollectiveOps's implementation of multi-worker all-reduce to to keep variables in sync. A collective op is a single op in the TensorFlow graph which can automatically choose an all-reduce algorithm in the TensorFlow runtime according to hardware, network topology and tensor sizes.

By default it uses all local GPUs or CPU for single-worker training.

When 'TF_CONFIG' environment variable is set, it parses cluster_spec, task_type and task_id from 'TF_CONFIG' and turns into a multi-worker strategy which mirrored models on GPUs of all machines in a cluster. In the current implementation, it uses all GPUs in a cluster and it assumes all workers have the same number of GPUs.

You can also pass a distribute.cluster_resolver.ClusterResolver instance when instantiating the strategy. The task_type, task_id etc. will be parsed from the resolver instance instead of from the TF_CONFIG env var.

It supports both eager mode and graph mode. However, for eager mode, it has to set up the eager context in its constructor and therefore all ops in eager mode have to run after the strategy object is created.

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

Methods

`experimental_distribute_dataset`

View source

experimental_distribute_dataset(
    dataset
)

Distributes a tf.data.Dataset instance provided via dataset.

The returned distributed dataset can be iterated over similar to how regular datasets can. NOTE: Currently, the user cannot add any more transformations to a distributed dataset.

The following is an example:

strategy = tf.distribute.MirroredStrategy()

# Create a dataset
dataset = dataset_ops.Dataset.TFRecordDataset([
  "/a/1.tfr", "/a/2.tfr", "/a/3.tfr", "/a/4.tfr"])

# Distribute that dataset
dist_dataset = strategy.experimental_distribute_dataset(dataset)

# Iterate over the distributed dataset
for x in dist_dataset:
  # process dataset elements
  strategy.run(train_step, args=(x,))

We will assume that the input dataset is batched by the global batch size. With this assumption, we will make a best effort to divide each batch across all the replicas (one or more workers).

In a multi-worker setting, we will first attempt to distribute the dataset by attempting to detect whether the dataset is being created out of ReaderDatasets (e.g. TFRecordDataset, TextLineDataset, etc.) and if so, attempting to shard the input files. Note that there has to be at least one input file per worker. If you have less than one input file per worker, we suggest that you should disable distributing your dataset using the method below.

If that attempt is unsuccessful (e.g. the dataset is created from a Dataset.range), we will shard the dataset evenly at the end by appending a .shard operation to the end of the processing pipeline. This will cause the entire preprocessing pipeline for all the data to be run on every worker, and each worker will do redundant work. We will print a warning if this method of sharding is selected.

You can disable dataset sharding across workers using the auto_shard_policy option in tf.data.experimental.DistributeOptions.

Within each worker, we will also split the data among all the worker devices (if more than one a present), and this will happen even if multi-worker sharding is disabled using the method above.

If the above batch splitting and dataset sharding logic is undesirable, please use experimental_distribute_datasets_from_function instead, which does not do any automatic splitting or sharding.

You can also use the element_spec property of the distributed dataset returned by this API to query the tf.TypeSpec of the elements returned by the iterator. This can be used to set the input_signature property of a tf.function.

strategy = tf.distribute.MirroredStrategy()

# Create a dataset
dataset = dataset_ops.Dataset.TFRecordDataset([
  "/a/1.tfr", "/a/2.tfr", "/a/3.tfr", "/a/4.tfr"])

# Distribute that dataset
dist_dataset = strategy.experimental_distribute_dataset(dataset)

@tf.function(input_signature=[dist_dataset.element_spec])
def train_step(inputs):
  # train model with inputs
  return

# Iterate over the distributed dataset
for x in dist_dataset:
  # process dataset elements
  strategy.run(train_step, args=(x,))

Args
`dataset`	`tf.data.Dataset` that will be sharded across all replicas using the rules stated above.

Returns
A "distributed `Dataset`", which acts like a `tf.data.Dataset` except it produces "per-replica" values.

`experimental_distribute_datasets_from_function`

View source

experimental_distribute_datasets_from_function(
    dataset_fn
)

Distributes tf.data.Dataset instances created by calls to dataset_fn.

dataset_fn will be called once for each worker in the strategy. Each replica on that worker will dequeue one batch of inputs from the local Dataset (i.e. if a worker has two replicas, two batches will be dequeued from the Dataset every step).

This method can be used for several purposes. For example, where experimental_distribute_dataset is unable to shard the input files, this method might be used to manually shard the dataset (avoiding the slow fallback behavior in experimental_distribute_dataset). In cases where the dataset is infinite, this sharding can be done by creating dataset replicas that differ only in their random seed. experimental_distribute_dataset may also sometimes fail to split the batch across replicas on a worker. In that case, this method can be used where that limitation does not exist.

The dataset_fn should take an tf.distribute.InputContext instance where information about batching and input replication can be accessed:

def dataset_fn(input_context):
  batch_size = input_context.get_per_replica_batch_size(global_batch_size)
  d = tf.data.Dataset.from_tensors([[1.]]).repeat().batch(batch_size)
  return d.shard(
      input_context.num_input_pipelines, input_context.input_pipeline_id)

inputs = strategy.experimental_distribute_datasets_from_function(dataset_fn)

for batch in inputs:
  replica_results = strategy.run(replica_fn, args=(batch,))

To query the tf.TypeSpec of the elements in the distributed dataset returned by this API, you need to use the element_spec property of the distributed iterator. This tf.TypeSpec can be used to set the input_signature property of a tf.function.

# If you want to specify `input_signature` for a `tf.function` you must
# first create the iterator.
iterator = iter(inputs)

@tf.function(input_signature=[iterator.element_spec])
def replica_fn_with_signature(inputs):
  # train the model with inputs
  return

for _ in range(steps):
  strategy.run(replica_fn_with_signature,
      args=(next(iterator),))

Args
`dataset_fn`	A function taking a `tf.distribute.InputContext` instance and returning a `tf.data.Dataset`.

Returns
A "distributed `Dataset`", which acts like a `tf.data.Dataset` except it produces "per-replica" values.

`experimental_local_results`

View source

experimental_local_results(
    value
)

Returns the list of all local per-replica values contained in value.

Args
`value`	A value returned by `experimental_run()`, `run()`, `extended.call_for_each_replica()`, or a variable created in `scope`.

Returns
A tuple of values contained in `value`. If `value` represents a single value, this returns `(value,).`

`experimental_make_numpy_dataset`

View source

experimental_make_numpy_dataset(
    numpy_input, session=None
)

Makes a tf.data.Dataset for input provided via a numpy array.

This avoids adding numpy_input as a large constant in the graph, and copies the data to the machine or machines that will be processing the input.

Note that you will likely need to use tf.distribute.Strategy.experimental_distribute_dataset with the returned dataset to further distribute it with the strategy.

Example:

numpy_input = np.ones([10], dtype=np.float32)
dataset = strategy.experimental_make_numpy_dataset(numpy_input)
dist_dataset = strategy.experimental_distribute_dataset(dataset)

Args
`numpy_input`	A nest of NumPy input arrays that will be converted into a dataset. Note that lists of Numpy arrays are stacked, as that is normal `tf.data.Dataset` behavior.
`session`	(TensorFlow v1.x graph execution only) A session used for initialization.

Returns
A `tf.data.Dataset` representing `numpy_input`.

`experimental_run`

View source

experimental_run(
    fn, input_iterator=None
)

Runs ops in fn on each replica, with inputs from input_iterator.

DEPRECATED: This method is not available in TF 2.x. Please switch to using run instead.

When eager execution is enabled, executes ops specified by fn on each replica. Otherwise, builds a graph to execute the ops on each replica.

Each replica will take a single, different input from the inputs provided by one get_next call on the input iterator.

fn may call tf.distribute.get_replica_context() to access members such as replica_id_in_sync_group.

Args
`fn`	The function to run. The inputs to the function must match the outputs of `input_iterator.get_next()`. The output must be a `tf.nest` of `Tensor`s.
`input_iterator`	(Optional) input iterator from which the inputs are taken.

Returns
Merged return value of `fn` across replicas. The structure of the return value is the same as the return value from `fn`. Each element in the structure can either be `PerReplica` (if the values are unsynchronized), `Mirrored` (if the values are kept in sync), or `Tensor` (if running on a single replica).

`make_dataset_iterator`

View source

make_dataset_iterator(
    dataset
)

Makes an iterator for input provided via dataset.

DEPRECATED: This method is not available in TF 2.x.

Data from the given dataset will be distributed evenly across all the compute replicas. We will assume that the input dataset is batched by the global batch size. With this assumption, we will make a best effort to divide each batch across all the replicas (one or more workers). If this effort fails, an error will be thrown, and the user should instead use make_input_fn_iterator which provides more control to the user, and does not try to divide a batch across replicas.

The user could also use make_input_fn_iterator if they want to customize which input is fed to which replica/worker etc.

Args
`dataset`	`tf.data.Dataset` that will be distributed evenly across all replicas.

Returns
An `tf.distribute.InputIterator` which returns inputs for each step of the computation. User should call `initialize` on the returned iterator.

`make_input_fn_iterator`

View source

make_input_fn_iterator(
    input_fn, replication_mode=tf.distribute.InputReplicationMode.PER_WORKER
)

Returns an iterator split across replicas created from an input function.

DEPRECATED: This method is not available in TF 2.x.

The input_fn should take an tf.distribute.InputContext object where information about batching and input sharding can be accessed:

def input_fn(input_context):
  batch_size = input_context.get_per_replica_batch_size(global_batch_size)
  d = tf.data.Dataset.from_tensors([[1.]]).repeat().batch(batch_size)
  return d.shard(input_context.num_input_pipelines,
                 input_context.input_pipeline_id)
with strategy.scope():
  iterator = strategy.make_input_fn_iterator(input_fn)
  replica_results = strategy.experimental_run(replica_fn, iterator)

The tf.data.Dataset returned by input_fn should have a per-replica batch size, which may be computed using input_context.get_per_replica_batch_size.

Args
`input_fn`	A function taking a `tf.distribute.InputContext` object and returning a `tf.data.Dataset`.
`replication_mode`	an enum value of `tf.distribute.InputReplicationMode`. Only `PER_WORKER` is supported currently, which means there will be a single call to `input_fn` per worker. Replicas will dequeue from the local `tf.data.Dataset` on their worker.

Returns
An iterator object that should first be `.initialize()`-ed. It may then either be passed to `strategy.experimental_run()` or you can `iterator.get_next()` to get the next value to pass to `strategy.extended.call_for_each_replica()`.

`reduce`

View source

reduce(
    reduce_op, value, axis=None
)

Reduce value across replicas.

Given a per-replica value returned by run, say a per-example loss, the batch will be divided across all the replicas. This function allows you to aggregate across replicas and optionally also across batch elements. For example, if you have a global batch size of 8 and 2 replicas, values for examples [0, 1, 2, 3] will be on replica 0 and [4, 5, 6, 7] will be on replica 1. By default, reduce will just aggregate across replicas, returning [0+4, 1+5, 2+6, 3+7]. This is useful when each replica is computing a scalar or some other value that doesn't have a "batch" dimension (like a gradient). More often you will want to aggregate across the global batch, which you can get by specifying the batch dimension as the axis, typically axis=0. In this case it would return a scalar 0+1+2+3+4+5+6+7.

If there is a last partial batch, you will need to specify an axis so that the resulting shape is consistent across replicas. So if the last batch has size 6 and it is divided into [0, 1, 2, 3] and [4, 5], you would get a shape mismatch unless you specify axis=0. If you specify tf.distribute.ReduceOp.MEAN, using axis=0 will use the correct denominator of 6. Contrast this with computing reduce_mean to get a scalar value on each replica and this function to average those means, which will weigh some values 1/8 and others 1/4.

Args
`reduce_op`	A `tf.distribute.ReduceOp` value specifying how values should be combined.
`value`	A "per replica" value, e.g. returned by `run` to be combined into a single tensor.
`axis`	Specifies the dimension to reduce along within each replica's tensor. Should typically be set to the batch dimension, or `None` to only reduce across replicas (e.g. if the tensor has no batch dimension).

Returns
A `Tensor`.

`run`

View source

run(
    fn, args=(), kwargs=None, options=None
)

Run fn on each replica, with the given arguments.

Executes ops specified by fn on each replica. If args or kwargs have tf.distribute.DistributedValues, such as those produced by a "distributed Dataset" or experimental_distribute_values_from_function when fn is executed on a particular replica, it will be executed with the component of tf.distribute.DistributedValues that correspond to that replica.

fn may call tf.distribute.get_replica_context() to access members such as all_reduce.

All arguments in args or kwargs should either be nest of tensors or tf.distribute.DistributedValues containing tensors or composite tensors.

Example usage:

Constant tensor input.

strategy = tf.distribute.MirroredStrategy()
tensor_input = tf.constant(3.0)
@tf.function
def replica_fn(input):
  return input*2.0
result = strategy.run(replica_fn, args=(tensor_input,))
result
<tf.Tensor: shape=(), dtype=float32, numpy=6.0>

DistributedValues input.

strategy = tf.distribute.MirroredStrategy()
@tf.function
def run():
  def value_fn(value_context):
    return value_context.num_replicas_in_sync
  distributed_values = (
    strategy.experimental_distribute_values_from_function(
      value_fn))
  def replica_fn2(input):
    return input*2
  return strategy.run(replica_fn2, args=(distributed_values,))
result = run()
result
<tf.Tensor: shape=(), dtype=int32, numpy=2>

Args
`fn`	The function to run. The output must be a `tf.nest` of `Tensor`s.
`args`	(Optional) Positional arguments to `fn`.
`kwargs`	(Optional) Keyword arguments to `fn`.
`options`	(Optional) An instance of `tf.distribute.RunOptions` specifying the options to run `fn`.

Returns
Merged return value of `fn` across replicas. The structure of the return value is the same as the return value from `fn`. Each element in the structure can either be `tf.distribute.DistributedValues`, `Tensor` objects, or `Tensor`s (for example, if running on a single replica).

`scope`

View source

scope()

Returns a context manager selecting this Strategy as current.

Inside a with strategy.scope(): code block, this thread will use a variable creator set by strategy, and will enter its "cross-replica context".

Returns
A context manager.

`update_config_proto`

View source

update_config_proto(
    config_proto
)

Returns a copy of config_proto modified for use with this strategy.

DEPRECATED: This method is not available in TF 2.x.

The updated config has something needed to run a strategy, e.g. configuration to run collective ops, or device filters to improve distributed training performance.

Args
`config_proto`	a `tf.ConfigProto` object.

Returns
The updated copy of the `config_proto`.

tf.compat.v1.distribute.experimental.MultiWorkerMirroredStrategy

Attributes

Methods

experimental_distribute_dataset

experimental_distribute_datasets_from_function

experimental_local_results

experimental_make_numpy_dataset

Example:

experimental_run

make_dataset_iterator

make_input_fn_iterator

reduce

run

Example usage:

scope

update_config_proto

`experimental_distribute_dataset`

`experimental_distribute_datasets_from_function`

`experimental_local_results`

`experimental_make_numpy_dataset`

`experimental_run`

`make_dataset_iterator`

`make_input_fn_iterator`

`reduce`

`run`

`scope`

`update_config_proto`