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import warnings
from collections import OrderedDict
import torch.distributed as dist
from mmcv.runner import OptimizerHook
from torch._utils import (_flatten_dense_tensors, _take_tensors,
_unflatten_dense_tensors)
def _allreduce_coalesced(tensors, world_size, bucket_size_mb=-1):
if bucket_size_mb > 0:
bucket_size_bytes = bucket_size_mb * 1024 * 1024
buckets = _take_tensors(tensors, bucket_size_bytes)
else:
buckets = OrderedDict()
for tensor in tensors:
tp = tensor.type()
if tp not in buckets:
buckets[tp] = []
buckets[tp].append(tensor)
buckets = buckets.values()
for bucket in buckets:
flat_tensors = _flatten_dense_tensors(bucket)
dist.all_reduce(flat_tensors)
flat_tensors.div_(world_size)
for tensor, synced in zip(
bucket, _unflatten_dense_tensors(flat_tensors, bucket)):
tensor.copy_(synced)
def allreduce_grads(params, coalesce=True, bucket_size_mb=-1):
"""Allreduce gradients.
Args:
params (list[torch.Parameters]): List of parameters of a model
coalesce (bool, optional): Whether allreduce parameters as a whole.
Defaults to True.
bucket_size_mb (int, optional): Size of bucket, the unit is MB.
Defaults to -1.
"""
grads = [
param.grad.data for param in params
if param.requires_grad and param.grad is not None
]
world_size = dist.get_world_size()
if coalesce:
_allreduce_coalesced(grads, world_size, bucket_size_mb)
else:
for tensor in grads:
dist.all_reduce(tensor.div_(world_size))
class DistOptimizerHook(OptimizerHook):
"""Deprecated optimizer hook for distributed training."""
def __init__(self, *args, **kwargs):
warnings.warn('"DistOptimizerHook" is deprecated, please switch to'
'"mmcv.runner.OptimizerHook".')
super().__init__(*args, **kwargs)
def reduce_mean(tensor):
""""Obtain the mean of tensor on different GPUs."""
if not (dist.is_available() and dist.is_initialized()):
return tensor
tensor = tensor.clone()
dist.all_reduce(tensor.div_(dist.get_world_size()), op=dist.ReduceOp.SUM)
return tensor
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