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# coding=utf-8
# Copyright (c) 2020, NVIDIA CORPORATION. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import torch
from .initialize import get_tensor_model_parallel_group, get_tensor_model_parallel_world_size, get_tensor_model_parallel_rank
from .utils import split_tensor_along_last_dim
def _reduce(input_):
"""All-reduce the input tensor across model parallel group."""
# Bypass the function if we are using only 1 GPU.
if get_tensor_model_parallel_world_size()==1:
return input_
# All-reduce.
torch.distributed.all_reduce(input_, group=get_tensor_model_parallel_group())
return input_
def _split_along_last_dim(input_):
"""Split the tensor along its last dimension and keep the
corresponding slice."""
world_size = get_tensor_model_parallel_world_size()
# Bypass the function if we are using only 1 GPU.
if world_size == 1:
return input_
# Split along last dimension.
input_list = split_tensor_along_last_dim(input_, world_size)
# Note: torch.split does not create contiguous tensors by default.
rank = get_tensor_model_parallel_rank()
output = input_list[rank].contiguous()
return output
def _split_along_first_dim(input_):
"""Split the tensor along its first dimension and keep the
corresponding slice."""
world_size = get_tensor_model_parallel_world_size()
# Bypass the function if we are using only 1 GPU.
if world_size == 1:
return input_
# Split along first dimension.
dim_size = input_.size()[0]
assert dim_size % world_size == 0, \
"First dimension of the tensor should be divisible by tensor parallel size"
local_dim_size = dim_size // world_size
rank = get_tensor_model_parallel_rank()
dim_offset = rank * local_dim_size
output = input_[dim_offset:dim_offset+local_dim_size].contiguous()
return output
def _gather_along_last_dim(input_):
"""Gather tensors and concatinate along the last dimension."""
world_size = get_tensor_model_parallel_world_size()
# Bypass the function if we are using only 1 GPU.
if world_size == 1:
return input_
# Size and dimension.
last_dim = input_.dim() - 1
rank = get_tensor_model_parallel_rank()
tensor_list = [torch.empty_like(input_) for _ in range(world_size)]
tensor_list[rank] = input_
torch.distributed.all_gather(tensor_list, input_, group=get_tensor_model_parallel_group())
# Note: torch.cat already creates a contiguous tensor.
output = torch.cat(tensor_list, dim=last_dim).contiguous()
return output
def _gather_along_first_dim(input_):
"""Gather tensors and concatinate along the first dimension."""
world_size = get_tensor_model_parallel_world_size()
# Bypass the function if we are using only 1 GPU.
if world_size == 1:
return input_
dim_size = list(input_.size())
dim_size[0] = dim_size[0] * world_size
output = torch.empty(dim_size, dtype=input_.dtype,
device=torch.cuda.current_device())
torch.distributed._all_gather_base(output, input_.contiguous(),
group=get_tensor_model_parallel_group())
return output
def _reduce_scatter_along_first_dim(input_):
"""Reduce-scatter the input tensor across model parallel group."""
world_size = get_tensor_model_parallel_world_size()
# Bypass the function if we are using only 1 GPU.
if world_size == 1:
return input_
dim_size = list(input_.size())
assert dim_size[0] % world_size == 0, \
"First dimension of the tensor should be divisible by tensor parallel size"
dim_size[0] = dim_size[0] // world_size
output = torch.empty(dim_size, dtype=input_.dtype,
device=torch.cuda.current_device())
torch.distributed._reduce_scatter_base(output, input_.contiguous(),
group=get_tensor_model_parallel_group())
return output
class _CopyToModelParallelRegion(torch.autograd.Function):
"""Pass the input to the model parallel region."""
@staticmethod
def symbolic(graph, input_):
return input_
@staticmethod
def forward(ctx, input_):
return input_
@staticmethod
def backward(ctx, grad_output):
return _reduce(grad_output)
class _ReduceFromModelParallelRegion(torch.autograd.Function):
"""All-reduce the input from the model parallel region."""
@staticmethod
def symbolic(graph, input_):
return _reduce(input_)
@staticmethod
def forward(ctx, input_):
return _reduce(input_)
@staticmethod
def backward(ctx, grad_output):
return grad_output
class _ScatterToModelParallelRegion(torch.autograd.Function):
"""Split the input and keep only the corresponding chuck to the rank."""
@staticmethod
def symbolic(graph, input_):
return _split_along_last_dim(input_)
@staticmethod
def forward(ctx, input_):
return _split_along_last_dim(input_)
@staticmethod
def backward(ctx, grad_output):
return _gather_along_last_dim(grad_output)
class _GatherFromModelParallelRegion(torch.autograd.Function):
"""Gather the input from model parallel region and concatinate."""
@staticmethod
def symbolic(graph, input_):
return _gather_along_last_dim(input_)
@staticmethod
def forward(ctx, input_):
return _gather_along_last_dim(input_)
@staticmethod
def backward(ctx, grad_output):
return _split_along_last_dim(grad_output)
class _ScatterToSequenceParallelRegion(torch.autograd.Function):
"""Split the input and keep only the corresponding chuck to the rank."""
@staticmethod
def symbolic(graph, input_):
return _split_along_first_dim(input_)
@staticmethod
def forward(ctx, input_):
return _split_along_first_dim(input_)
@staticmethod
def backward(ctx, grad_output):
return _gather_along_first_dim(grad_output)
class _GatherFromSequenceParallelRegion(torch.autograd.Function):
"""Gather the input from sequence parallel region and concatinate."""
@staticmethod
def symbolic(graph, input_, tensor_parallel_output_grad=True):
return _gather_along_first_dim(input_)
@staticmethod
def forward(ctx, input_, tensor_parallel_output_grad=True):
ctx.tensor_parallel_output_grad = tensor_parallel_output_grad
return _gather_along_first_dim(input_)
@staticmethod
def backward(ctx, grad_output):
tensor_parallel_output_grad = ctx.tensor_parallel_output_grad
# If the computation graph after the gather operation is
# in the tensor parallel mode, output gradients need to reduce
# scattered and whereas if the computation is duplicated,
# output gradients need to be scattered.
if tensor_parallel_output_grad:
return _reduce_scatter_along_first_dim(grad_output), None
else:
return _split_along_first_dim(grad_output), None
class _ReduceScatterToSequenceParallelRegion(torch.autograd.Function):
"""Reduce scatter the input from the model parallel region."""
@staticmethod
def symbolic(graph, input_):
return _reduce_scatter_along_first_dim(input_)
@staticmethod
def forward(ctx, input_):
return _reduce_scatter_along_first_dim(input_)
@staticmethod
def backward(ctx, grad_output):
return _gather_along_first_dim(grad_output)
# -----------------
# Helper functions.
# -----------------
def copy_to_tensor_model_parallel_region(input_):
return _CopyToModelParallelRegion.apply(input_)
def reduce_from_tensor_model_parallel_region(input_):
return _ReduceFromModelParallelRegion.apply(input_)
def scatter_to_tensor_model_parallel_region(input_):
return _ScatterToModelParallelRegion.apply(input_)
def gather_from_tensor_model_parallel_region(input_):
return _GatherFromModelParallelRegion.apply(input_)
def scatter_to_sequence_parallel_region(input_):
return _ScatterToSequenceParallelRegion.apply(input_)
def gather_from_sequence_parallel_region(input_, tensor_parallel_output_grad=True):
return _GatherFromSequenceParallelRegion.apply(input_, tensor_parallel_output_grad)
def reduce_scatter_to_sequence_parallel_region(input_):
return _ReduceScatterToSequenceParallelRegion.apply(input_)
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