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# SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0
#
# 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.
from typing import Callable
import torch
from megatron.core import ModelParallelConfig, parallel_state
from megatron.core.tensor_parallel import ColumnParallelLinear as McoreColumnParallelLinear
from megatron.core.tensor_parallel import RowParallelLinear as McoreRowParallelLinear
from megatron.core.tensor_parallel import VocabParallelEmbedding as McoreVocabParallelEmbedding
from megatron.core.tensor_parallel.mappings import (
reduce_from_tensor_model_parallel_region,
reduce_scatter_to_sequence_parallel_region,
)
from megatron.core.tensor_parallel.utils import VocabUtility
from torch.distributed import _functional_collectives as funcol
from torch.distributed._functional_collectives import all_reduce
class VocabParallelEmbedding(torch.nn.Module):
"""
Embedding parallelized in the vocabulary dimension.
This is mainly adapted from torch.nn.Embedding and all the default
values are kept.
Args:
num_embeddings (int): vocabulary size.
embedding_dim (int): size of hidden state.
precision (str): precision of the embedding.
"""
def __init__(
self,
num_embeddings: int,
embedding_dim: int,
precision: str = "bfloat16",
):
super().__init__()
self.num_embeddings = num_embeddings
self.embedding_dim = embedding_dim
self.tensor_model_parallel_size = parallel_state.get_tensor_model_parallel_world_size()
# Divide the weight matrix along the vocaburaly dimension.
(self.vocab_start_index, self.vocab_end_index) = VocabUtility.vocab_range_from_global_vocab_size(
self.num_embeddings,
parallel_state.get_tensor_model_parallel_rank(),
self.tensor_model_parallel_size,
)
self.num_embeddings_per_partition = self.vocab_end_index - self.vocab_start_index
self.weight = torch.nn.Parameter(
torch.empty(
self.num_embeddings_per_partition,
self.embedding_dim,
device=torch.cuda.current_device(),
dtype=getattr(torch, precision),
)
)
def forward(self, input_):
"""Forward.
Args:
input_ (torch.Tensor): Input tensor.
"""
if self.tensor_model_parallel_size > 1:
# Build the mask.
input_mask = (input_ < self.vocab_start_index) | (input_ >= self.vocab_end_index)
# Mask the input.
masked_input = input_.clone() - self.vocab_start_index
masked_input[input_mask] = 0
else:
masked_input = input_
# Get the embeddings.
output = self.weight[masked_input]
# Mask the output embedding.
if self.tensor_model_parallel_size > 1:
output[input_mask, :] = 0.0
output = all_reduce(output, "sum", group=parallel_state.get_tensor_model_parallel_group())
return output
class ColumnParallelLinear(McoreColumnParallelLinear):
"""
A modified version of Mcore's ColumnParallelLinear that only returns the output tensor.
"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def forward(self, input_: torch.Tensor):
"""
Performs the forward pass of the column parallel linear layer.
Args:
input_ (torch.Tensor): The input tensor.
weight (Optional[torch.Tensor], optional): The weight tensor. If None, uses the layer's own weight.
Returns:
torch.Tensor: The output tensor after the linear transformation.
"""
output, _ = super().forward(input_)
return output
class RowParallelLinear(McoreRowParallelLinear):
"""
A modified version of Mcore's RowParallelLinear that only returns the output tensor.
"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def forward(self, input_: torch.Tensor):
"""
Performs the forward pass of the Row Parallel linear layer.
Args:
input_ (torch.Tensor): The input tensor.
weight (Optional[torch.Tensor], optional): The weight tensor. If None, uses the layer's own weight.
Returns:
torch.Tensor: The output tensor after the linear transformation.
"""
output, _ = super().forward(input_)
return output
class TrainingVocabParallelEmbedding(McoreVocabParallelEmbedding):
"""
Embedding parallelized in the vocabulary dimension.
This is mainly adapted from torch.nn.Embedding and all the default
values are kept.
Args:
num_embeddings (int): vocabulary size.
embedding_dim (int): size of hidden state.
Keyword Args:
sequence_parallel (bool): Decides whether to perform ReduceScatter after embedding lookup
batch_first (bool): If True, then output tensor shape is [batch, seq, feature]. If False, then shape becomes
[seq, batch, feature]. Note: We assume the input tensor is always in the shape of [seq, batch].
config: A megatron.core.ModelParallelConfig object
use_inference_allreduce (bool): If True, then Megatron's allreduce in the forward pass is disabled, and the pytorch's
allreduce is used instead (inference mode only).
"""
def __init__(
self,
num_embeddings: int,
embedding_dim: int,
*,
init_method: Callable,
sequence_parallel: bool = False,
batch_first: bool = False,
config: ModelParallelConfig,
use_inference_allreduce: bool = False,
):
super(TrainingVocabParallelEmbedding, self).__init__(
num_embeddings=num_embeddings,
embedding_dim=embedding_dim,
init_method=init_method,
config=config,
)
self.sequence_parallel = sequence_parallel
if sequence_parallel:
# If sequence parallel, then the output tensor should be in the shape of [seq, batch, feature]
batch_first = False
self.batch_first = batch_first
self.use_inference_allreduce = use_inference_allreduce
def forward(self, input_):
"""Forward.
Args:
input_ (torch.Tensor): Input tensor.
"""
if self.tensor_model_parallel_size > 1:
# Build the mask.
input_mask = (input_ < self.vocab_start_index) | (input_ >= self.vocab_end_index)
# Mask the input.
masked_input = input_.clone() - self.vocab_start_index
masked_input[input_mask] = 0
else:
masked_input = input_
# Get the embeddings.
output = self.weight[masked_input]
# Mask the output embedding.
if self.tensor_model_parallel_size > 1:
output[input_mask, :] = 0.0
if self.sequence_parallel:
assert not self.batch_first
# Data format change to avoid explicit tranposes : [b s h] --> [s b h].
output = output.transpose(0, 1).contiguous()
if not self.use_inference_allreduce:
output = reduce_scatter_to_sequence_parallel_region(output)
else:
# Reduce across all the model parallel GPUs.
if not self.use_inference_allreduce:
output = reduce_from_tensor_model_parallel_region(output)
if not self.batch_first:
# Shape: [b, s, h] --> [s, b, h]
output = output.transpose(0, 1).contiguous()
if self.use_inference_allreduce:
output = funcol.all_reduce(output, "sum", group=parallel_state.get_tensor_model_parallel_group())
return output