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import inspect
from typing import Any, Callable, Dict, List, Optional, Set, TYPE_CHECKING
from collections import OrderedDict
import logging
import torch
from torch.fx._compatibility import compatibility
from torch.fx.graph_module import GraphModule
from torch.fx.node import Node
if TYPE_CHECKING:
import sympy # noqa: F401
__all__ = ["Partition", "split_module"]
_LOGGER = logging.getLogger(__name__)
@compatibility(is_backward_compatible=True)
class Partition:
def __init__(self, name: str):
self.name: str = name
self.submod_name = f"submod_{name}"
self.node_names: List[str] = []
self.inputs: Dict[str, None] = {}
self.outputs: Dict[str, None] = {}
self.dependencies: Dict[str, None] = {}
self.dependents: Dict[str, None] = {}
self.graph: torch.fx.graph.Graph = torch.fx.graph.Graph()
self.environment: Dict[Node, Node] = {}
self.targets: Dict[str, Any] = {}
def __repr__(self) -> str:
return (
f"name: {self.name},\n"
f" nodes: {self.node_names},\n"
f" inputs: {self.inputs},\n"
f" outputs: {self.outputs},\n"
f" partitions depended on: {self.dependencies},\n"
f" partition dependents: {self.dependents}"
)
# Creates subgraphs out of main graph
@compatibility(is_backward_compatible=True)
def split_module(
m: GraphModule,
root_m: torch.nn.Module,
split_callback: Callable[[Node], int],
qualname_map: Optional[Dict[str, str]] = None,
keep_original_order: Optional[bool] = False,
keep_original_node_name: Optional[bool] = False,
):
"""
Creates subgraphs out of main graph
Args:
m (GraphModule): Graph module to split
root_m (torch.nn.Module): root nn module. Not currently used. Included
because the root nn module is usually transformed via
torch.fx._symbolic_trace.symbolic_trace (see example below)
split_callback (Callable[[Node], int]): Callable function
that maps a given Node instance to a numeric partition identifier.
split_module will use this function as the policy for which operations
appear in which partitions in the output Module.
qualname_map: Optional[Dict[str, str]]: optional output parameter that returns a
mapping from new target names in the module after split to old target
names in the original module.
keep_original_order: Optional[bool]: keep the original order of the GraphModule
or use the Topological order of the new constructed GraphModule
Returns:
GraphModule: the module after split.
Example:
This is a sample setup:
import torch
from torch.fx.symbolic_trace import symbolic_trace
from torch.fx.graph_module import GraphModule
from torch.fx.node import Node
from torch.fx.passes.split_module import split_module
class MyModule(torch.nn.Module):
def __init__(self):
super().__init__()
self.param = torch.nn.Parameter(torch.rand(3, 4))
self.linear = torch.nn.Linear(4, 5)
def forward(self, x, y):
z = self.linear(x + self.param).clamp(min=0.0, max=1.0)
w = self.linear(y).clamp(min=0.0, max=1.0)
return z + w
# symbolically trace model
my_module = MyModule()
my_module_traced = symbolic_trace(my_module)
# random mod partitioning
partition_counter = 0
NPARTITIONS = 3
def mod_partition(node: Node):
global partition_counter
partition = partition_counter % NPARTITIONS
partition_counter = (partition_counter + 1) % NPARTITIONS
return partition
# split module in module with submodules
module_with_submodules = split_module(
my_module_traced, my_module, mod_partition
)
Output looks like this. Original graph is broken into partitions
> print(module_with_submodules)
GraphModule(
(submod_0): GraphModule(
(linear): Linear(in_features=4, out_features=5, bias=True)
)
(submod_1): GraphModule(
(linear): Linear(in_features=4, out_features=5, bias=True)
)
(submod_2): GraphModule()
)
def forward(self, x, y):
param = self.param
submod_0 = self.submod_0(x, param, y); x = param = y = None
getitem = submod_0[0]
getitem_1 = submod_0[1]; submod_0 = None
submod_1 = self.submod_1(getitem, getitem_1); getitem = getitem_1 = None
getitem_2 = submod_1[0]
getitem_3 = submod_1[1]; submod_1 = None
submod_2 = self.submod_2(getitem_2, getitem_3); getitem_2 = getitem_3 = None
return submod_2
Output of split module is the same as output of input traced module.
This is an example within a test setting:
> orig_out = my_module_traced(x, y)
> submodules_out = module_with_submodules(x, y)
> self.assertEqual(orig_out, submodules_out)
True
"""
def construct_graph(
node: Node,
base_mod_env: Dict[str, Node],
base_mod_attrs: Dict[str, torch.fx.graph_module.GraphModule],
):
if node.op == "placeholder":
default_value = (
node.args[0] if len(node.args) > 0 else inspect.Signature.empty
)
if keep_original_node_name:
args = () if default_value is inspect.Signature.empty else (default_value,)
base_mod_env[node.name] = base_mod_graph.create_node('placeholder', node.name, args=args, type_expr=node.type)
else:
base_mod_env[node.name] = base_mod_graph.placeholder(
node.target, type_expr=node.type, default_value=default_value
)
base_mod_env[node.name].meta = node.meta.copy()
elif node.op == "get_attr":
base_mod_env[node.name] = base_mod_graph.get_attr(node.target)
base_mod_env[node.name].meta = node.meta.copy()
attr_val = m
for atom in node.target.split("."): # type: ignore[union-attr]
if not hasattr(attr_val, atom):
raise AttributeError(f"Node target {node.target} not found!")
attr_val = getattr(attr_val, atom)
base_mod_attrs[node.target] = attr_val # type: ignore[index]
return base_mod_env, base_mod_attrs
partitions: Dict[str, Partition] = {}
orig_nodes: Dict[str, Node] = {}
symbol_to_node: Dict["sympy.Symbol", Node] = {}
def record_cross_partition_use(
def_node: Node, use_node: Optional[Node]
): # noqa: B950
from torch.fx.experimental.symbolic_shapes import free_symbols
defined = getattr(def_node, "_fx_partition", None)
used = getattr(use_node, "_fx_partition", None)
if defined != used:
if defined is not None:
def_partition = partitions[defined]
def_partition.outputs.setdefault(def_node.name)
if used is not None:
def_partition.dependents.setdefault(used)
if used is not None:
use_partition = partitions[used]
use_partition.inputs.setdefault(def_node.name)
if (def_val := def_node.meta.get("example_value")) is not None:
for s in sorted(free_symbols(def_val), key=str):
use_partition.inputs.setdefault(symbol_to_node[s].name)
if defined is not None:
use_partition.dependencies.setdefault(defined)
def instantiate_node_partition_mapping(node):
partition_name = str(split_callback(node))
# add node to partitions
partition = partitions.get(partition_name)
if partition is None:
partitions[partition_name] = partition = Partition(partition_name)
partition.node_names.append(node.name)
node._fx_partition = partition_name
# Global State Nodes are nodes which by their global state effects,
# "taint" all downstream nodes while they are active.
GLOBAL_STATE_NODES = [
torch.amp._enter_autocast,
torch.amp._exit_autocast,
torch._C._set_grad_enabled
]
# For grad regions:
# ------------------------
# 1. first region: we do nothing
# 2. subsequent regions: we insert the set_grad at the beginning
grad_regions: OrderedDict[Node, Set[int]] = OrderedDict()
# For autocast regions:
# ------------------------
# 1. first region: we will only insert the _exit at the end
# 2. intermediate regions: we will insert both the
# _enter at the beginning and _exit at the end
# 3. last region: we will only insert _enter at the beginning
# We will do so in the order in which the autocasts were instantiated.
autocast_regions: OrderedDict[Node, Set[int]] = OrderedDict()
autocast_exits: Dict[Node, Optional[Node]] = {}
active_grad = None
active_autocasts = set()
import sympy # noqa: F811
for node in m.graph.nodes:
if node.op in ["placeholder", "get_attr", "output"]:
if (
node.op == "placeholder" and
(val := node.meta.get("example_value")) is not None and
isinstance(val, torch.SymInt) and
isinstance(val.node.expr, sympy.Symbol)
):
symbol_to_node[val.node.expr] = node
continue
instantiate_node_partition_mapping(node)
if node.op == "call_function" and node.target in GLOBAL_STATE_NODES:
if node.target == torch._C._set_grad_enabled:
assert len(node.args) == 1
assert isinstance(node.args[0], bool)
active_grad = node
grad_regions[active_grad] = set({split_callback(node)})
elif node.target == torch.amp._enter_autocast:
# Should all be python constants
assert all(not isinstance(arg, Node) for arg in node.args)
active_autocasts.add(node)
autocast_regions[node] = set({split_callback(node)})
autocast_exits[node] = None
elif node.target == torch.amp._exit_autocast:
assert len(node.args) == 1
autocast_regions[node.args[0]].add(split_callback(node))
active_autocasts.remove(node.args[0])
autocast_exits[node.args[0]] = node
if active_grad is not None:
grad_regions[active_grad].add(split_callback(node))
for a in active_autocasts:
autocast_regions[a].add(split_callback(node))
assert all(v is not None for v in autocast_exits.values()), "autocast must exit"
autocast_regions = {k: sorted(v) for k, v in autocast_regions.items()}
grad_regions = {k: sorted(v) for k, v in grad_regions.items()}
if _LOGGER.isEnabledFor(logging.DEBUG):
_LOGGER.debug("autocast_regions: %s", autocast_regions)
_LOGGER.debug("grad_regions: %s", grad_regions)
assert_monotonically_increasing = bool(autocast_regions) or bool(grad_regions)
# split nodes into partitions
highest_partition = -1
for node in m.graph.nodes:
orig_nodes[node.name] = node
# TODO currently placeholders/parameters aren't put into random partitions,
# rather they're added to the graphs where they are used down below
if node.op in ["placeholder", "get_attr"]:
continue
if node.op == "output":
torch.fx.graph.map_arg(
node.args[0], lambda n: record_cross_partition_use(n, None)
)
continue
if assert_monotonically_increasing:
pid = split_callback(node)
assert highest_partition <= pid, \
("autocast or set_grad_enabled require monotonically increasing partitions:"
f"highest: {highest_partition}, this node's: {pid}")
highest_partition = pid
# do not capture cross-partition dependencies for global state nodes as they will be
# self-contained - their setup and unwind will be isolated to each partition submodule.
if node.target not in GLOBAL_STATE_NODES:
torch.fx.graph.map_arg(
node.args, lambda def_node: record_cross_partition_use(def_node, node)
)
torch.fx.graph.map_arg(
node.kwargs, lambda def_node: record_cross_partition_use(def_node, node)
) # noqa: B950
original_partition_order = list(partitions.keys())
# find partitions with no dependencies
root_partitions: List[str] = []
for partition_name, partition in partitions.items():
if not len(partition.dependencies):
root_partitions.append(partition_name)
# check partitions for circular dependencies and create topological partition ordering
sorted_partitions: List[str] = []
while root_partitions:
root_partition = root_partitions.pop()
sorted_partitions.append(root_partition)
for dependent in partitions[root_partition].dependents:
partitions[dependent].dependencies.pop(root_partition)
if not partitions[dependent].dependencies:
root_partitions.append(dependent)
if len(sorted_partitions) != len(partitions):
raise RuntimeError("cycle exists between partitions!")
# Enter prelude
for regions_mapping in [autocast_regions, grad_regions]:
for node, regions in regions_mapping.items():
assert len(regions) > 0
partitions[str(regions[0])].environment[node] = node
for r in regions[1:]:
partition = partitions[str(r)]
new_node = partition.graph.create_node(
op=node.op,
target=node.target,
args=tuple(arg for arg in node.args),
kwargs={},
type_expr=node.type,
)
new_node.meta = node.meta.copy() # is it really a good idea to copy this?
partition.environment[node] = new_node
# add placeholders to partition inputs
for partition_name in sorted_partitions:
partition = partitions[partition_name]
for inp in partition.inputs:
placeholder = partition.graph.placeholder(
inp,
type_expr=orig_nodes[inp].type,
)
placeholder.meta = orig_nodes[inp].meta.copy()
partition.environment[orig_nodes[inp]] = placeholder
# Transform nodes and collect targets for partition's submodule
for node in m.graph.nodes:
if hasattr(node, "_fx_partition"):
partition = partitions[node._fx_partition]
# swap out old graph nodes in kw/args with references to new nodes in this submodule
environment = partition.environment
gathered_args = torch.fx.graph.map_arg(node.args, lambda n: environment[n])
gathered_kwargs = torch.fx.graph.map_arg(
node.kwargs, lambda n: environment[n]
)
if node.op not in ["call_module", "get_attr"]:
target = node.target
else:
target_atoms = node.target.split(".")
target_attr = m
for atom in target_atoms:
if not hasattr(target_attr, atom):
raise AttributeError(f"Operator target {node.target} not found!")
target_attr = getattr(target_attr, atom)
# target = target_atoms[-1]
target = "_".join(target_atoms)
partition.targets[target] = target_attr
# Fill in the passed-in mapping from new qualname to old qualname
if qualname_map is not None:
# When creating the split module later, the submodules will have
# path prefix matching the corresponding partition's submod_name
qualname = f"{partition.submod_name}.{target}"
qualname_map[qualname] = node.target
assert isinstance(gathered_args, tuple)
assert isinstance(gathered_kwargs, dict)
name = node.name if keep_original_node_name else None
new_node = partition.graph.create_node(
op=node.op,
target=target,
args=gathered_args,
kwargs=gathered_kwargs,
type_expr=node.type,
name=name,
)
new_node.meta = node.meta.copy()
partition.environment[node] = new_node
# Exit epilogue
for regions_mapping in [autocast_regions]:
for node in reversed(regions_mapping):
regions = regions_mapping[node]
assert len(regions) > 0
for r in regions[:-1]:
partition = partitions[str(r)]
exit_node = autocast_exits[node]
assert exit_node is not None, "Missing exit node"
new_node = partition.graph.create_node(
op=exit_node.op,
target=exit_node.target,
args=(partition.environment[node],),
kwargs={},
type_expr=exit_node.type,
)
new_node.meta = exit_node.meta.copy() # is it really a good idea to copy this?
# original module environment dict mapping node names to nodes
orig_mod_env: Dict[str, Node] = {}
# Set up values to construct base module
base_mod_env: Dict[str, Node] = {}
base_mod_graph: torch.fx.graph.Graph = torch.fx.graph.Graph()
base_mod_attrs: Dict[str, torch.fx.graph_module.GraphModule] = {}
if not keep_original_order:
for node in m.graph.nodes:
base_mod_env, base_mod_attrs = construct_graph(
node, base_mod_env, base_mod_attrs
)
else:
# Go through the graph to construct the mapping dict
for node in m.graph.nodes:
orig_mod_env[node.name] = node
# Do some things iterating over the partitions in topological order again:
# 1) Finish off submodule Graphs by setting corresponding outputs
# 2) Construct GraphModules for each submodule
# 3) Construct the base graph by emitting calls to those submodules in
# topological order or original order specified by keep_original_order
construct_order_partitions = (
sorted_partitions if not keep_original_order else original_partition_order
)
already_constructed_attr_nodes = set()
for partition_name in construct_order_partitions:
partition = partitions[partition_name]
# Set correct output values
output_vals = tuple(
partition.environment[orig_nodes[name]] for name in partition.outputs
)
# skip output node generation if there are no output values
num_output_vals = len(output_vals)
if num_output_vals == 1:
partition.graph.output(output_vals[0])
elif num_output_vals > 1:
partition.graph.output(output_vals)
if keep_original_order:
# first get the attr nodes required by this partition
orig_mod_attr_nodes: List[Node] = [
orig_mod_env[key] for key in partition.inputs
]
# Construct GraphModule for this partition
for node in orig_mod_attr_nodes: # type: ignore[attr-defined]
if node in already_constructed_attr_nodes:
continue
base_mod_env, base_mod_attrs = construct_graph(
node, base_mod_env, base_mod_attrs
)
already_constructed_attr_nodes.add(node)
base_mod_attrs[partition.submod_name] = torch.fx.graph_module.GraphModule(
partition.targets, partition.graph
) # noqa: B950
# Emit call in base graph to this submodule
output_val = base_mod_graph.call_module(
partition.submod_name,
tuple(base_mod_env[name] for name in partition.inputs),
)
num_outputs = len(partition.outputs)
if num_outputs > 1:
# Unpack multiple return values from submodule
output_val_proxy = torch.fx.proxy.Proxy(output_val)
for i, output_name in enumerate(partition.outputs):
base_mod_env[output_name] = output_val_proxy[i].node # type: ignore[index]
elif num_outputs == 1:
base_mod_env[next(iter(partition.outputs))] = output_val
for node in m.graph.nodes:
if node.op == "output":
base_mod_graph.output(
torch.fx.graph.map_arg(node.args[0], lambda n: base_mod_env[n.name])
) # noqa: B950
return torch.fx.graph_module.GraphModule(base_mod_attrs, base_mod_graph)
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