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# Copyright 2025 The HuggingFace Team. 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 inspect
from dataclasses import dataclass
from typing import Dict, List, Type, Union
import torch
if torch.distributed.is_available():
import torch.distributed._functional_collectives as funcol
from ..models._modeling_parallel import (
ContextParallelConfig,
ContextParallelInput,
ContextParallelModelPlan,
ContextParallelOutput,
)
from ..utils import get_logger
from ..utils.torch_utils import unwrap_module
from .hooks import HookRegistry, ModelHook
logger = get_logger(__name__) # pylint: disable=invalid-name
_CONTEXT_PARALLEL_INPUT_HOOK_TEMPLATE = "cp_input---{}"
_CONTEXT_PARALLEL_OUTPUT_HOOK_TEMPLATE = "cp_output---{}"
# TODO(aryan): consolidate with ._helpers.TransformerBlockMetadata
@dataclass
class ModuleForwardMetadata:
cached_parameter_indices: Dict[str, int] = None
_cls: Type = None
def _get_parameter_from_args_kwargs(self, identifier: str, args=(), kwargs=None):
kwargs = kwargs or {}
if identifier in kwargs:
return kwargs[identifier], True, None
if self.cached_parameter_indices is not None:
index = self.cached_parameter_indices.get(identifier, None)
if index is None:
raise ValueError(f"Parameter '{identifier}' not found in cached indices.")
return args[index], False, index
if self._cls is None:
raise ValueError("Model class is not set for metadata.")
parameters = list(inspect.signature(self._cls.forward).parameters.keys())
parameters = parameters[1:] # skip `self`
self.cached_parameter_indices = {param: i for i, param in enumerate(parameters)}
if identifier not in self.cached_parameter_indices:
raise ValueError(f"Parameter '{identifier}' not found in function signature but was requested.")
index = self.cached_parameter_indices[identifier]
if index >= len(args):
raise ValueError(f"Expected {index} arguments but got {len(args)}.")
return args[index], False, index
def apply_context_parallel(
module: torch.nn.Module,
parallel_config: ContextParallelConfig,
plan: Dict[str, ContextParallelModelPlan],
) -> None:
"""Apply context parallel on a model."""
logger.debug(f"Applying context parallel with CP mesh: {parallel_config._mesh} and plan: {plan}")
for module_id, cp_model_plan in plan.items():
submodule = _get_submodule_by_name(module, module_id)
if not isinstance(submodule, list):
submodule = [submodule]
logger.debug(f"Applying ContextParallelHook to {module_id=} identifying a total of {len(submodule)} modules")
for m in submodule:
if isinstance(cp_model_plan, dict):
hook = ContextParallelSplitHook(cp_model_plan, parallel_config)
hook_name = _CONTEXT_PARALLEL_INPUT_HOOK_TEMPLATE.format(module_id)
elif isinstance(cp_model_plan, (ContextParallelOutput, list, tuple)):
if isinstance(cp_model_plan, ContextParallelOutput):
cp_model_plan = [cp_model_plan]
if not all(isinstance(x, ContextParallelOutput) for x in cp_model_plan):
raise ValueError(f"Expected all elements of cp_model_plan to be CPOutput, but got {cp_model_plan}")
hook = ContextParallelGatherHook(cp_model_plan, parallel_config)
hook_name = _CONTEXT_PARALLEL_OUTPUT_HOOK_TEMPLATE.format(module_id)
else:
raise ValueError(f"Unsupported context parallel model plan type: {type(cp_model_plan)}")
registry = HookRegistry.check_if_exists_or_initialize(m)
registry.register_hook(hook, hook_name)
def remove_context_parallel(module: torch.nn.Module, plan: Dict[str, ContextParallelModelPlan]) -> None:
for module_id, cp_model_plan in plan.items():
submodule = _get_submodule_by_name(module, module_id)
if not isinstance(submodule, list):
submodule = [submodule]
for m in submodule:
registry = HookRegistry.check_if_exists_or_initialize(m)
if isinstance(cp_model_plan, dict):
hook_name = _CONTEXT_PARALLEL_INPUT_HOOK_TEMPLATE.format(module_id)
elif isinstance(cp_model_plan, (ContextParallelOutput, list, tuple)):
hook_name = _CONTEXT_PARALLEL_OUTPUT_HOOK_TEMPLATE.format(module_id)
else:
raise ValueError(f"Unsupported context parallel model plan type: {type(cp_model_plan)}")
registry.remove_hook(hook_name)
class ContextParallelSplitHook(ModelHook):
def __init__(self, metadata: ContextParallelModelPlan, parallel_config: ContextParallelConfig) -> None:
super().__init__()
self.metadata = metadata
self.parallel_config = parallel_config
self.module_forward_metadata = None
def initialize_hook(self, module):
cls = unwrap_module(module).__class__
self.module_forward_metadata = ModuleForwardMetadata(_cls=cls)
return module
def pre_forward(self, module, *args, **kwargs):
args_list = list(args)
for name, cpm in self.metadata.items():
if isinstance(cpm, ContextParallelInput) and cpm.split_output:
continue
# Maybe the parameter was passed as a keyword argument
input_val, is_kwarg, index = self.module_forward_metadata._get_parameter_from_args_kwargs(
name, args_list, kwargs
)
if input_val is None:
continue
# The input_val may be a tensor or list/tuple of tensors. In certain cases, user may specify to shard
# the output instead of input for a particular layer by setting split_output=True
if isinstance(input_val, torch.Tensor):
input_val = self._prepare_cp_input(input_val, cpm)
elif isinstance(input_val, (list, tuple)):
if len(input_val) != len(cpm):
raise ValueError(
f"Expected input model plan to have {len(input_val)} elements, but got {len(cpm)}."
)
sharded_input_val = []
for i, x in enumerate(input_val):
if torch.is_tensor(x) and not cpm[i].split_output:
x = self._prepare_cp_input(x, cpm[i])
sharded_input_val.append(x)
input_val = sharded_input_val
else:
raise ValueError(f"Unsupported input type: {type(input_val)}")
if is_kwarg:
kwargs[name] = input_val
elif index is not None and index < len(args_list):
args_list[index] = input_val
else:
raise ValueError(
f"An unexpected error occurred while processing the input '{name}'. Please open an "
f"issue at https://github.com/huggingface/diffusers/issues and provide a minimal reproducible "
f"example along with the full stack trace."
)
return tuple(args_list), kwargs
def post_forward(self, module, output):
is_tensor = isinstance(output, torch.Tensor)
is_tensor_list = isinstance(output, (list, tuple)) and all(isinstance(x, torch.Tensor) for x in output)
if not is_tensor and not is_tensor_list:
raise ValueError(f"Expected output to be a tensor or a list/tuple of tensors, but got {type(output)}.")
output = [output] if is_tensor else list(output)
for index, cpm in self.metadata.items():
if not isinstance(cpm, ContextParallelInput) or not cpm.split_output:
continue
if index >= len(output):
raise ValueError(f"Index {index} out of bounds for output of length {len(output)}.")
current_output = output[index]
current_output = self._prepare_cp_input(current_output, cpm)
output[index] = current_output
return output[0] if is_tensor else tuple(output)
def _prepare_cp_input(self, x: torch.Tensor, cp_input: ContextParallelInput) -> torch.Tensor:
if cp_input.expected_dims is not None and x.dim() != cp_input.expected_dims:
logger.warning_once(
f"Expected input tensor to have {cp_input.expected_dims} dimensions, but got {x.dim()} dimensions, split will not be applied."
)
return x
else:
return EquipartitionSharder.shard(x, cp_input.split_dim, self.parallel_config._flattened_mesh)
class ContextParallelGatherHook(ModelHook):
def __init__(self, metadata: ContextParallelModelPlan, parallel_config: ContextParallelConfig) -> None:
super().__init__()
self.metadata = metadata
self.parallel_config = parallel_config
def post_forward(self, module, output):
is_tensor = isinstance(output, torch.Tensor)
if is_tensor:
output = [output]
elif not (isinstance(output, (list, tuple)) and all(isinstance(x, torch.Tensor) for x in output)):
raise ValueError(f"Expected output to be a tensor or a list/tuple of tensors, but got {type(output)}.")
output = list(output)
if len(output) != len(self.metadata):
raise ValueError(f"Expected output to have {len(self.metadata)} elements, but got {len(output)}.")
for i, cpm in enumerate(self.metadata):
if cpm is None:
continue
output[i] = EquipartitionSharder.unshard(output[i], cpm.gather_dim, self.parallel_config._flattened_mesh)
return output[0] if is_tensor else tuple(output)
class AllGatherFunction(torch.autograd.Function):
@staticmethod
def forward(ctx, tensor, dim, group):
ctx.dim = dim
ctx.group = group
ctx.world_size = torch.distributed.get_world_size(group)
ctx.rank = torch.distributed.get_rank(group)
return funcol.all_gather_tensor(tensor, dim, group=group)
@staticmethod
def backward(ctx, grad_output):
grad_chunks = torch.chunk(grad_output, ctx.world_size, dim=ctx.dim)
return grad_chunks[ctx.rank], None, None
class EquipartitionSharder:
@classmethod
def shard(cls, tensor: torch.Tensor, dim: int, mesh: torch.distributed.device_mesh.DeviceMesh) -> torch.Tensor:
# NOTE: the following assertion does not have to be true in general. We simply enforce it for now
# because the alternate case has not yet been tested/required for any model.
assert tensor.size()[dim] % mesh.size() == 0, (
"Tensor size along dimension to be sharded must be divisible by mesh size"
)
# The following is not fullgraph compatible with Dynamo (fails in DeviceMesh.get_rank)
# return tensor.chunk(mesh.size(), dim=dim)[mesh.get_rank()]
return tensor.chunk(mesh.size(), dim=dim)[torch.distributed.get_rank(mesh.get_group())]
@classmethod
def unshard(cls, tensor: torch.Tensor, dim: int, mesh: torch.distributed.device_mesh.DeviceMesh) -> torch.Tensor:
tensor = tensor.contiguous()
tensor = AllGatherFunction.apply(tensor, dim, mesh.get_group())
return tensor
def _get_submodule_by_name(model: torch.nn.Module, name: str) -> Union[torch.nn.Module, List[torch.nn.Module]]:
if name.count("*") > 1:
raise ValueError("Wildcard '*' can only be used once in the name")
return _find_submodule_by_name(model, name)
def _find_submodule_by_name(model: torch.nn.Module, name: str) -> Union[torch.nn.Module, List[torch.nn.Module]]:
if name == "":
return model
first_atom, remaining_name = name.split(".", 1) if "." in name else (name, "")
if first_atom == "*":
if not isinstance(model, torch.nn.ModuleList):
raise ValueError("Wildcard '*' can only be used with ModuleList")
submodules = []
for submodule in model:
subsubmodules = _find_submodule_by_name(submodule, remaining_name)
if not isinstance(subsubmodules, list):
subsubmodules = [subsubmodules]
submodules.extend(subsubmodules)
return submodules
else:
if hasattr(model, first_atom):
submodule = getattr(model, first_atom)
return _find_submodule_by_name(submodule, remaining_name)
else:
raise ValueError(f"'{first_atom}' is not a submodule of '{model.__class__.__name__}'")
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