# Copyright The Lightning AI team.
#
# 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 io
import os
from typing import TYPE_CHECKING, Any, Optional, Union
import torch
from torch import Tensor
from torch.nn import Module
from typing_extensions import override
import lightning.pytorch as pl
from lightning.fabric.accelerators.xla import _XLA_AVAILABLE, _XLA_GREATER_EQUAL_2_1
from lightning.fabric.plugins import XLACheckpointIO
from lightning.fabric.plugins.environments import XLAEnvironment
from lightning.fabric.strategies import _StrategyRegistry
from lightning.fabric.utilities.optimizer import _optimizers_to_device
from lightning.fabric.utilities.types import _PATH, ReduceOp
from lightning.pytorch.plugins import XLAPrecision
from lightning.pytorch.plugins.io.wrapper import _WrappingCheckpointIO
from lightning.pytorch.strategies.ddp import DDPStrategy
from lightning.pytorch.strategies.launchers.xla import _XLALauncher
from lightning.pytorch.strategies.strategy import TBroadcast
from lightning.pytorch.trainer.states import TrainerFn
from lightning.pytorch.utilities import find_shared_parameters, set_shared_parameters
from lightning.pytorch.utilities.rank_zero import rank_zero_only
if TYPE_CHECKING:
from torch_xla.distributed.parallel_loader import MpDeviceLoader
[docs]class XLAStrategy(DDPStrategy):
"""Strategy for training multiple TPU devices using the :func:`torch_xla.distributed.xla_multiprocessing.spawn`
method."""
strategy_name = "xla"
def __init__(
self,
accelerator: Optional["pl.accelerators.Accelerator"] = None,
parallel_devices: Optional[list[torch.device]] = None,
checkpoint_io: Optional[Union[XLACheckpointIO, _WrappingCheckpointIO]] = None,
precision_plugin: Optional[XLAPrecision] = None,
debug: bool = False,
sync_module_states: bool = True,
**_: Any,
) -> None:
if not _XLA_AVAILABLE:
raise ModuleNotFoundError(str(_XLA_AVAILABLE))
super().__init__(
accelerator=accelerator,
parallel_devices=parallel_devices,
cluster_environment=XLAEnvironment(),
checkpoint_io=checkpoint_io,
precision_plugin=precision_plugin,
start_method="fork",
)
self.debug = debug
self._launched = False
self._sync_module_states = sync_module_states
@property
@override
def checkpoint_io(self) -> Union[XLACheckpointIO, _WrappingCheckpointIO]:
plugin = self._checkpoint_io
if plugin is not None:
assert isinstance(plugin, (XLACheckpointIO, _WrappingCheckpointIO))
return plugin
return XLACheckpointIO()
@checkpoint_io.setter
@override
def checkpoint_io(self, io: Optional[Union[XLACheckpointIO, _WrappingCheckpointIO]]) -> None:
if io is not None and not isinstance(io, (XLACheckpointIO, _WrappingCheckpointIO)):
raise TypeError(f"The XLA strategy can only work with the `XLACheckpointIO` plugin, found {io}")
self._checkpoint_io = io
@property
@override
def precision_plugin(self) -> XLAPrecision:
plugin = self._precision_plugin
if plugin is not None:
assert isinstance(plugin, XLAPrecision)
return plugin
return XLAPrecision()
@precision_plugin.setter
@override
def precision_plugin(self, precision_plugin: Optional[XLAPrecision]) -> None:
if precision_plugin is not None and not isinstance(precision_plugin, XLAPrecision):
raise TypeError(f"The XLA strategy can only work with the `XLAPrecision` plugin, found {precision_plugin}")
self._precision_plugin = precision_plugin
@property
@override
def root_device(self) -> torch.device:
if not self._launched:
raise RuntimeError("Accessing the XLA device before processes have spawned is not allowed.")
import torch_xla.core.xla_model as xm
return xm.xla_device()
@property
@override
def global_rank(self) -> int:
return super().global_rank if self._launched else 0
@property
@override
def local_rank(self) -> int:
return super().local_rank if self._launched else 0
@property
@override
def node_rank(self) -> int:
return super().node_rank if self._launched else 0
@property
@override
def world_size(self) -> int:
return super().world_size if self._launched else 1
@override
def _configure_launcher(self) -> None:
self._launcher = _XLALauncher(self)
[docs] @override
def setup(self, trainer: "pl.Trainer") -> None:
assert self.accelerator is not None
self.accelerator.setup(trainer)
if self.debug:
os.environ["PT_XLA_DEBUG"] = "1"
assert self.model is not None
self.precision_plugin.convert_module(self.model)
shared_params = find_shared_parameters(self.model)
self.model_to_device()
set_shared_parameters(self.model, shared_params)
self.model = self._setup_model(self.model)
if self._sync_module_states:
if _XLA_GREATER_EQUAL_2_1:
from torch_xla.core.xla_model import broadcast_master_param
else:
from torch_xla.experimental.pjrt import broadcast_master_param
broadcast_master_param(self.model)
if trainer.state.fn == TrainerFn.FITTING:
self.setup_optimizers(trainer)
self.setup_precision_plugin()
if trainer.state.fn == TrainerFn.FITTING:
_optimizers_to_device(self.optimizers, self.root_device)
@override
def _setup_model(self, model: Module) -> Module: # type: ignore
return model
@property
@override
def distributed_sampler_kwargs(self) -> dict[str, int]:
return {"num_replicas": self.world_size, "rank": self.global_rank}
[docs] @override
def process_dataloader(self, dataloader: object) -> "MpDeviceLoader":
from torch_xla.distributed.parallel_loader import MpDeviceLoader
if isinstance(dataloader, MpDeviceLoader):
# dataloader is already wrapped by MpDeviceLoader
return dataloader
dataloader = MpDeviceLoader(dataloader, self.root_device)
# Mimic interface to torch.utils.data.DataLoader
dataloader.dataset = dataloader._loader.dataset
dataloader.batch_sampler = getattr(dataloader._loader, "batch_sampler", None)
return dataloader
@override
def configure_ddp(self) -> None:
pass
[docs] @override
def model_to_device(self) -> None:
assert self.model is not None
self.model = self.model.to(self.root_device)
[docs] @override
def barrier(self, name: Optional[str] = None, *args: Any, **kwargs: Any) -> None:
if not self._launched:
return
import torch_xla.core.xla_model as xm
if name is None:
# `None` is not supported: "TypeError: _xla_rendezvous(): incompatible function arguments"
name = ""
xm.rendezvous(name)
[docs] @override
def broadcast(self, obj: TBroadcast, src: int = 0) -> TBroadcast:
if not self._launched:
return obj
import torch_xla.core.xla_model as xm
is_tensor = isinstance(obj, Tensor)
if is_tensor:
if obj.dim() == 0:
obj = obj.unsqueeze(0)
original_device = obj.device
# XLA distributed requires that the data is on the XLA device
obj = obj.to(self.root_device)
else:
# support for arbitrary pickle-ables
buffer = io.BytesIO()
torch.save(obj, buffer)
obj = torch.tensor( # type: ignore[assignment]
bytearray(buffer.getbuffer()), device=self.root_device, dtype=torch.float
)
obj = [obj]
xm.collective_broadcast(obj, root_ordinal=src)
obj = obj[0]
if not is_tensor:
# this will preserve the dtype and device of any tensors
buffer = io.BytesIO(obj.cpu().byte().numpy())
obj = torch.load(buffer)
else:
obj = obj.to(original_device)
return obj
[docs] @override
def reduce(
self, output: Union[Tensor, Any], group: Optional[Any] = None, reduce_op: Optional[Union[ReduceOp, str]] = None
) -> Tensor:
if not isinstance(output, Tensor):
output = torch.tensor(output, device=self.root_device)
invalid_reduce_op = isinstance(reduce_op, ReduceOp) and reduce_op != ReduceOp.SUM
invalid_reduce_op_str = isinstance(reduce_op, str) and reduce_op.lower() not in ("sum", "mean", "avg")
if invalid_reduce_op or invalid_reduce_op_str:
raise ValueError(
"Currently, the XLAStrategy only supports `sum`, `mean`, `avg` for the reduce operation, got:"
f" {reduce_op}"
)
import torch_xla.core.xla_model as xm
output = xm.mesh_reduce("reduce", output, sum)
if isinstance(reduce_op, str) and reduce_op.lower() in ("avg", "mean"):
output = output / self.world_size
return output
[docs] @override
def setup_environment(self) -> None:
self._launched = True
super().setup_environment()
@override
def setup_distributed(self) -> None:
assert self.parallel_devices is not None
if len(self.parallel_devices) == 1:
# spawning only 1 device with PjRT is not supported:
# https://github.com/Lightning-AI/lightning/pull/17408#discussion_r1170671732
raise NotImplementedError(
"The `XLAStrategy` does not support running on a single device with the PjRT runtime."
" Try using all devices or the `SingleDeviceXLAStrategy` strategy"
)
rank_zero_only.rank = self.global_rank
@override
def set_world_ranks(self) -> None:
# accessing global_rank will initialize the XLA computation client. since this is called outside of the spawned
# processes (by the accelerator connector), we cannot run the code that would normally be here.
# instead it's done in `setup_distributed`
pass
[docs] @override
def save_checkpoint(
self, checkpoint: dict[str, Any], filepath: _PATH, storage_options: Optional[Any] = None
) -> None:
import torch_xla.core.xla_model as xm
# sync any pending lazy tensors on all ranks before saving to prevent potential collective hangs
xm.mark_step()
# save on global rank zero only
super().save_checkpoint(checkpoint, filepath, storage_options=storage_options)
[docs] @override
def remove_checkpoint(self, filepath: _PATH) -> None:
"""Remove checkpoint filepath from the filesystem.
Args:
filepath: Path to checkpoint
"""
if self.local_rank == 0:
self.checkpoint_io.remove_checkpoint(filepath)
[docs] @override
def all_gather(self, tensor: Tensor, group: Optional[Any] = None, sync_grads: bool = False) -> Tensor:
"""Function to gather a tensor from several distributed processes.
Args:
tensor: tensor to all-gather.
group: unused.
sync_grads: flag that allows users to synchronize gradients for the all-gather operation.
Return:
A tensor of shape (world_size, ...)
"""
if not self._launched:
return tensor
if not isinstance(tensor, Tensor):
raise NotImplementedError(
f"`{type(self).__name__}.all_gather` is only implemented for tensors. Given {tensor}"
)
if tensor.dim() == 0:
tensor = tensor.unsqueeze(0)
original_device = tensor.device
tensor = tensor.to(self.root_device)
import torch_xla.core.functions as xf
import torch_xla.core.xla_model as xm
tensor = xf.all_gather(tensor) if sync_grads else xm.all_gather(tensor)
tensor = tensor.to(original_device)
return tensor
[docs] @override
def teardown(self) -> None:
super().teardown()
self._launched = False # after the Trainer finishes, we aren't inside the spawned region
os.environ.pop("PT_XLA_DEBUG", None)
@classmethod
@override
def register_strategies(cls, strategy_registry: _StrategyRegistry) -> None:
strategy_registry.register("xla_debug", cls, description="XLA strategy with `debug` as True", debug=True)
strategy_registry.register(
cls.strategy_name,
cls,
description=cls.__name__,
)
