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import torch
import torch.distributed as dist
from torch.nn.modules import Module
from torch.autograd import Variable
def _flatten_dense_tensors(tensors):
"""Flatten dense tensors into a contiguous 1D buffer. Assume tensors are of
same dense type.
Since inputs are dense, the resulting tensor will be a concatenated 1D
buffer. Element-wise operation on this buffer will be equivalent to
operating individually.
Arguments:
tensors (Iterable[Tensor]): dense tensors to flatten.
Returns:
A contiguous 1D buffer containing input tensors.
"""
if len(tensors) == 1:
return tensors[0].contiguous().view(-1)
flat = torch.cat([t.contiguous().view(-1) for t in tensors], dim=0)
return flat
def _unflatten_dense_tensors(flat, tensors):
"""View a flat buffer using the sizes of tensors. Assume that tensors are of
same dense type, and that flat is given by _flatten_dense_tensors.
Arguments:
flat (Tensor): flattened dense tensors to unflatten.
tensors (Iterable[Tensor]): dense tensors whose sizes will be used to
unflatten flat.
Returns:
Unflattened dense tensors with sizes same as tensors and values from
flat.
"""
outputs = []
offset = 0
for tensor in tensors:
numel = tensor.numel()
outputs.append(flat.narrow(0, offset, numel).view_as(tensor))
offset += numel
return tuple(outputs)
'''
This version of DistributedDataParallel is designed to be used in conjunction with the multiproc.py
launcher included with this example. It assumes that your run is using multiprocess with 1
GPU/process, that the model is on the correct device, and that torch.set_device has been
used to set the device.
Parameters are broadcasted to the other processes on initialization of DistributedDataParallel,
and will be allreduced at the finish of the backward pass.
'''
class DistributedDataParallel(Module):
def __init__(self, module):
super(DistributedDataParallel, self).__init__()
#fallback for PyTorch 0.3
if not hasattr(dist, '_backend'):
self.warn_on_half = True
else:
self.warn_on_half = True if dist._backend == dist.dist_backend.GLOO else False
self.module = module
for p in self.module.state_dict().values():
if not torch.is_tensor(p):
continue
dist.broadcast(p, 0)
def allreduce_params():
if(self.needs_reduction):
self.needs_reduction = False
buckets = {}
for param in self.module.parameters():
if param.requires_grad and param.grad is not None:
tp = type(param.data)
if tp not in buckets:
buckets[tp] = []
buckets[tp].append(param)
if self.warn_on_half:
if torch.cuda.HalfTensor in buckets:
print("WARNING: gloo dist backend for half parameters may be extremely slow." +
" It is recommended to use the NCCL backend in this case. This currently requires" +
"PyTorch built from top of tree master.")
self.warn_on_half = False
for tp in buckets:
bucket = buckets[tp]
grads = [param.grad.data for param in bucket]
coalesced = _flatten_dense_tensors(grads)
dist.all_reduce(coalesced)
coalesced /= dist.get_world_size()
for buf, synced in zip(grads, _unflatten_dense_tensors(coalesced, grads)):
buf.copy_(synced)
for param in list(self.module.parameters()):
def allreduce_hook(*unused):
param._execution_engine.queue_callback(allreduce_params)
if param.requires_grad:
param.register_hook(allreduce_hook)
def forward(self, *inputs, **kwargs):
self.needs_reduction = True
return self.module(*inputs, **kwargs)
'''
def _sync_buffers(self):
buffers = list(self.module._all_buffers())
if len(buffers) > 0:
# cross-node buffer sync
flat_buffers = _flatten_dense_tensors(buffers)
dist.broadcast(flat_buffers, 0)
for buf, synced in zip(buffers, _unflatten_dense_tensors(flat_buffers, buffers)):
buf.copy_(synced)
def train(self, mode=True):
# Clear NCCL communicator and CUDA event cache of the default group ID,
# These cache will be recreated at the later call. This is currently a
# work-around for a potential NCCL deadlock.
if dist._backend == dist.dist_backend.NCCL:
dist._clear_group_cache()
super(DistributedDataParallel, self).train(mode)
self.module.train(mode)
'''
'''
Modifies existing model to do gradient allreduce, but doesn't change class
so you don't need "module"
'''
def apply_gradient_allreduce(module):
if not hasattr(dist, '_backend'):
module.warn_on_half = True
else:
module.warn_on_half = True if dist._backend == dist.dist_backend.GLOO else False
for p in module.state_dict().values():
if not torch.is_tensor(p):
continue
dist.broadcast(p, 0)
def allreduce_params():
if(module.needs_reduction):
module.needs_reduction = False
buckets = {}
for param in module.parameters():
if param.requires_grad and param.grad is not None:
tp = param.data.dtype
if tp not in buckets:
buckets[tp] = []
buckets[tp].append(param)
if module.warn_on_half:
if torch.cuda.HalfTensor in buckets:
print("WARNING: gloo dist backend for half parameters may be extremely slow." +
" It is recommended to use the NCCL backend in this case. This currently requires" +
"PyTorch built from top of tree master.")
module.warn_on_half = False
for tp in buckets:
bucket = buckets[tp]
grads = [param.grad.data for param in bucket]
coalesced = _flatten_dense_tensors(grads)
dist.all_reduce(coalesced)
coalesced /= dist.get_world_size()
for buf, synced in zip(grads, _unflatten_dense_tensors(coalesced, grads)):
buf.copy_(synced)
for param in list(module.parameters()):
def allreduce_hook(*unused):
Variable._execution_engine.queue_callback(allreduce_params)
if param.requires_grad:
param.register_hook(allreduce_hook)
def set_needs_reduction(self, input, output):
self.needs_reduction = True
module.register_forward_hook(set_needs_reduction)
return module
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