import torch
from ..modules import Module
from .scatter_gather import scatter_kwargs, gather
from .replicate import replicate
from .parallel_apply import parallel_apply
[docs]class DataParallel(Module):
r"""Implements data parallelism at the module level.
This container parallelizes the application of the given module by
splitting the input across the specified devices by chunking in the batch
dimension. In the forward pass, the module is replicated on each device,
and each replica handles a portion of the input. During the backwards
pass, gradients from each replica are summed into the original module.
The batch size should be larger than the number of GPUs used. It should
also be an integer multiple of the number of GPUs so that each chunk is the
same size (so that each GPU processes the same number of samples).
See also: :ref:`cuda-nn-dataparallel-instead`
Arbitrary positional and keyword inputs are allowed to be passed into
DataParallel EXCEPT Tensors. All variables will be scattered on dim
specified (default 0). Primitive types will be broadcasted, but all
other types will be a shallow copy and can be corrupted if written to in
the model's forward pass.
.. warning::
Forward and backwrad hooks defined on :attr:`module` and its submodules
won't be invoked anymore, unless the hooks are initialized in the
:meth:`forward` method.
Args:
module: module to be parallelized
device_ids: CUDA devices (default: all devices)
output_device: device location of output (default: device_ids[0])
Example::
>>> net = torch.nn.DataParallel(model, device_ids=[0, 1, 2])
>>> output = net(input_var)
"""
# TODO: update notes/cuda.rst when this class handles 8+ GPUs well
def __init__(self, module, device_ids=None, output_device=None, dim=0):
super(DataParallel, self).__init__()
if not torch.cuda.is_available():
self.module = module
self.device_ids = []
return
if device_ids is None:
device_ids = list(range(torch.cuda.device_count()))
if output_device is None:
output_device = device_ids[0]
self.dim = dim
self.module = module
self.device_ids = device_ids
self.output_device = output_device
if len(self.device_ids) == 1:
self.module.cuda(device_ids[0])
def forward(self, *inputs, **kwargs):
if not self.device_ids:
return self.module(*inputs, **kwargs)
inputs, kwargs = self.scatter(inputs, kwargs, self.device_ids)
if len(self.device_ids) == 1:
return self.module(*inputs[0], **kwargs[0])
replicas = self.replicate(self.module, self.device_ids[:len(inputs)])
outputs = self.parallel_apply(replicas, inputs, kwargs)
return self.gather(outputs, self.output_device)
def replicate(self, module, device_ids):
return replicate(module, device_ids)
def scatter(self, inputs, kwargs, device_ids):
return scatter_kwargs(inputs, kwargs, device_ids, dim=self.dim)
def parallel_apply(self, replicas, inputs, kwargs):
return parallel_apply(replicas, inputs, kwargs, self.device_ids[:len(replicas)])
def gather(self, outputs, output_device):
return gather(outputs, output_device, dim=self.dim)
def data_parallel(module, inputs, device_ids=None, output_device=None, dim=0, module_kwargs=None):
r"""Evaluates module(input) in parallel across the GPUs given in device_ids.
This is the functional version of the DataParallel module.
Args:
module: the module to evaluate in parallel
inputs: inputs to the module
device_ids: GPU ids on which to replicate module
output_device: GPU location of the output Use -1 to indicate the CPU.
(default: device_ids[0])
Returns:
a Variable containing the result of module(input) located on
output_device
"""
if not isinstance(inputs, tuple):
inputs = (inputs,)
if device_ids is None:
device_ids = list(range(torch.cuda.device_count()))
if output_device is None:
output_device = device_ids[0]
inputs, module_kwargs = scatter_kwargs(inputs, module_kwargs, device_ids, dim)
if len(device_ids) == 1:
return module(*inputs[0], **module_kwargs[0])
used_device_ids = device_ids[:len(inputs)]
replicas = replicate(module, used_device_ids)
outputs = parallel_apply(replicas, inputs, module_kwargs, used_device_ids)
return gather(outputs, output_device, dim)