Supporting Adding DDP Communication Hooks

CHANGELOG.md

@@ -63,6 +63,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Added support for `precision=64`, enabling training with double precision ([#6595](https://github.com/PyTorchLightning/pytorch-lightning/pull/6595))
 
+- Added support for DDP communication hooks ([#6736] (https://github.com/PyTorchLightning/pytorch-lightning/issues/6736))
 
 ### Changed
 

pytorch_lightning/plugins/training_type/ddp.py

@@ -29,14 +29,21 @@
 from pytorch_lightning.overrides.distributed import prepare_for_backward
 from pytorch_lightning.plugins.environments.cluster_environment import ClusterEnvironment
 from pytorch_lightning.plugins.training_type.parallel import ParallelPlugin
-from pytorch_lightning.utilities import _HYDRA_AVAILABLE, _TORCH_GREATER_EQUAL_1_7, rank_zero_warn
+from pytorch_lightning.utilities import (
+    _HYDRA_AVAILABLE,
+    _TORCH_GREATER_EQUAL_1_7,
+    _TORCH_GREATER_EQUAL_1_8,
+    rank_zero_warn,
+)
 from pytorch_lightning.utilities.distributed import rank_zero_only, ReduceOp, sync_ddp_if_available
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.seed import seed_everything
 
 if _HYDRA_AVAILABLE:
     from hydra.core.hydra_config import HydraConfig
     from hydra.utils import get_original_cwd, to_absolute_path
+if _TORCH_GREATER_EQUAL_1_8:
+    from pytorch_lightning.utilities.distributed import register_ddp_comm_hook
 
 log = logging.getLogger(__name__)
 
@@ -58,6 +65,9 @@ def __init__(
         num_nodes: int = 1,
         cluster_environment: ClusterEnvironment = None,
         sync_batchnorm: bool = False,
+        ddp_comm_state: Optional[object] = None,
+        ddp_comm_hook: Optional[callable] = None,
+        ddp_comm_wrapper: Optional[callable] = None,
         **kwargs: Union[Any, Dict[str, Any]],
     ) -> None:
         super().__init__(parallel_devices=parallel_devices, cluster_environment=cluster_environment)
@@ -70,6 +80,9 @@ def __init__(
         self.task_idx = None
         self.node_rank = 0
         self.num_processes = len(parallel_devices) if parallel_devices is not None else parallel_devices
+        self._ddp_comm_state = ddp_comm_state
+        self._ddp_comm_hook = ddp_comm_hook
+        self._ddp_comm_wrapper = ddp_comm_wrapper
 
     @property
     def root_device(self):
@@ -80,6 +93,10 @@ def distributed_sampler_kwargs(self):
         distributed_sampler_kwargs = dict(num_replicas=(self.num_nodes * self.num_processes), rank=self.global_rank)
         return distributed_sampler_kwargs
 
+    @property
+    def _is_single_process_single_device(self) -> bool:
+        return True
+
     def setup_environment(self):
         # start the other scripts
         if not self.cluster_environment.creates_children() and os.environ.get("PL_IN_DDP_SUBPROCESS", "0") != "1":
@@ -218,13 +235,30 @@ def pre_configure_ddp(self):
             )
             self._ddp_kwargs["find_unused_parameters"] = True
 
+    def _register_ddp_hooks(self) -> None:
+        # currently, DDP communication hooks only work with NCCL backend and SPSD (singlge process single device) mode
+        # https://github.com/pytorch/pytorch/blob/e6779d4357ae94cc9f9fedb83a87eb6126016769/
+        # torch/nn/parallel/distributed.py#L1040
+        if (
+            _TORCH_GREATER_EQUAL_1_8
+            and self.on_gpu
+            and self._is_single_process_single_device
+        ):
+            register_ddp_comm_hook(
+                model=self._model,
+                ddp_comm_state=self._ddp_comm_state,
+                ddp_comm_hook=self._ddp_comm_hook,
+                ddp_comm_wrapper=self._ddp_comm_wrapper,
+            )
+
     def configure_ddp(self):
         self.pre_configure_ddp()
         self._model = DistributedDataParallel(
             LightningDistributedModule(self.model),
             device_ids=self.determine_ddp_device_ids(),
             **self._ddp_kwargs,
         )
+        self._register_ddp_hooks()
 
     def determine_ddp_device_ids(self):
         if self.root_device.type == "cpu":

pytorch_lightning/plugins/training_type/ddp2.py

@@ -59,6 +59,10 @@ def distributed_sampler_kwargs(self):
         distributed_sampler_kwargs = dict(num_replicas=self.num_nodes, rank=self.global_rank)
         return distributed_sampler_kwargs
 
+    @property
+    def _is_single_process_single_device(self) -> bool:
+        return False
+
     def set_world_ranks(self):
         self.local_rank = self.task_idx
         self.node_rank = self.cluster_environment.node_rank()

pytorch_lightning/plugins/training_type/ddp_spawn.py

@@ -28,11 +28,13 @@
 from pytorch_lightning.plugins.environments.cluster_environment import ClusterEnvironment
 from pytorch_lightning.plugins.training_type.parallel import ParallelPlugin
 from pytorch_lightning.trainer.states import TrainerState
-from pytorch_lightning.utilities import _TORCH_GREATER_EQUAL_1_7
+from pytorch_lightning.utilities import _TORCH_GREATER_EQUAL_1_7, _TORCH_GREATER_EQUAL_1_8
 from pytorch_lightning.utilities.cloud_io import atomic_save
 from pytorch_lightning.utilities.cloud_io import load as pl_load
 from pytorch_lightning.utilities.distributed import rank_zero_only, rank_zero_warn, ReduceOp, sync_ddp_if_available
 from pytorch_lightning.utilities.seed import seed_everything
+if _TORCH_GREATER_EQUAL_1_8:
+    from pytorch_lightning.utilities.distributed import register_ddp_comm_hook
 
 log = logging.getLogger(__name__)
 
@@ -47,16 +49,22 @@ def __init__(
         num_nodes: int = 1,
         cluster_environment: ClusterEnvironment = None,
         sync_batchnorm: bool = False,
+        ddp_comm_state: Optional[object] = None,
+        ddp_comm_hook: Optional[callable] = None,
+        ddp_comm_wrapper: Optional[callable] = None,
         **kwargs: Union[Any, Dict[str, Any]],
     ):
         super().__init__(parallel_devices=parallel_devices, cluster_environment=cluster_environment)
         self.num_nodes = num_nodes
         self.sync_batchnorm = sync_batchnorm
         self._ddp_kwargs = kwargs
         self.dist = LightningDistributed()
-        self.num_processes = len(parallel_devices)
+        self.num_processes = len(parallel_devices) if parallel_devices is not None else 0
         self.node_rank = 0
         self.mp_queue = None
+        self._ddp_comm_state = ddp_comm_state
+        self._ddp_comm_hook = ddp_comm_hook
+        self._ddp_comm_wrapper = ddp_comm_wrapper
 
     def __getstate__(self):
         """ Makes this plugin pickleable without destroying the queue in the current process. """
@@ -76,9 +84,12 @@ def distributed_sampler_kwargs(self):
         distributed_sampler_kwargs = dict(num_replicas=(self.num_nodes * self.num_processes), rank=self.global_rank)
         return distributed_sampler_kwargs
 
+    @property
+    def _is_single_process_single_device(self):
+        return True
+
     def setup(self, model):
         os.environ["MASTER_PORT"] = str(self.cluster_environment.master_port())
-
         # pass in a state q
         smp = mp.get_context("spawn")
         self.mp_queue = smp.SimpleQueue()
@@ -181,13 +192,30 @@ def pre_configure_ddp(self):
             )
             self._ddp_kwargs["find_unused_parameters"] = True
 
+    def _register_ddp_hooks(self) -> None:
+        # currently, DDP communication hooks only work with NCCL backend and SPSD (singlge process single device) mode
+        # https://github.com/pytorch/pytorch/blob/e6779d4357ae94cc9f9fedb83a87eb6126016769/
+        # torch/nn/parallel/distributed.py#L1040
+        if (
+            _TORCH_GREATER_EQUAL_1_8
+            and self.on_gpu
+            and self._is_single_process_single_device
+        ):
+            register_ddp_comm_hook(
+                model=self._model,
+                ddp_comm_state=self._ddp_comm_state,
+                ddp_comm_hook=self._ddp_comm_hook,
+                ddp_comm_wrapper=self._ddp_comm_wrapper,
+            )
+
     def configure_ddp(self):
         self.pre_configure_ddp()
         self._model = DistributedDataParallel(
             LightningDistributedModule(self.model),
             device_ids=self.determine_ddp_device_ids(),
             **self._ddp_kwargs,
         )
+        self._register_ddp_hooks()
 
     def init_ddp_connection(self, global_rank: int, world_size: int) -> None:
         # TODO: this code is duplicated in DDP and DDPSpawn, make this a function

pytorch_lightning/utilities/__init__.py

@@ -39,6 +39,8 @@
     _RPC_AVAILABLE,
     _TORCH_GREATER_EQUAL_1_6,
     _TORCH_GREATER_EQUAL_1_7,
+    _TORCH_GREATER_EQUAL_1_8,
+    _TORCH_GREATER_EQUAL_1_9,
     _TORCH_LOWER_EQUAL_1_4,
     _TORCH_QUANTIZE_AVAILABLE,
     _TORCHTEXT_AVAILABLE,

pytorch_lightning/utilities/distributed.py

@@ -17,9 +17,15 @@
 import warnings
 from functools import wraps
 from typing import Any, Optional, Union
+from pytorch_lightning.utilities.imports import (
+    _TORCH_GREATER_EQUAL_1_8,
+    _TORCH_GREATER_EQUAL_1_9,
+)
 
 import torch
 
+from torch.nn.parallel.distributed import DistributedDataParallel
+
 log = logging.getLogger(__name__)
 
 if torch.distributed.is_available():
@@ -197,3 +203,107 @@ def all_gather_ddp_if_available(
             with torch.no_grad():
                 return AllGatherGrad.apply(tensor, group)
     return tensor
+
+
+def register_ddp_comm_hook(
+    model: DistributedDataParallel,
+    ddp_comm_state: Optional[object] = None,
+    ddp_comm_hook: Optional[callable] = None,
+    ddp_comm_wrapper: Optional[callable] = None,
+) -> None:
+    """
+    Function to register communication hook for DDP model
+    https://pytorch.org/docs/master/ddp_comm_hooks.html
+
+    Args:
+        model:
+            DDP model
+        ddp_comm_state:
+            state is passed to the hook and can be used to maintain
+            and update any state information that users would like to
+            maintain as part of the training process. Examples: error
+            feedback in gradient compression, peers to communicate with
+            next in GossipGrad etc.
+        ddp_comm_hook:
+            hook(state: object, bucket: dist._GradBucket) -> torch.futures.Future
+
+            This callable function is called once the bucket is ready. The
+            hook can perform whatever processing is needed and return
+            a Future indicating completion of any async work (ex: allreduce).
+            If the hook doesn't perform any communication, it can also
+            just return a completed Future. The Future should hold the
+            new value of grad bucket's tensors. Once a bucket is ready,
+            c10d reducer would call this hook and use the tensors returned
+            by the Future and copy grads to individual parameters.
+        ddp_comm_wrapper:
+            communication hook wraper to support a communication hook such
+            as FP16 compression as wrapper, which could be combined with
+            ddp_comm_hook
+
+    .. warning ::
+        DDP communication hook needs pytorch version at least 1.8.0
+
+    .. warning ::
+        DDP communication wrapper needs pytorch version at least 1.9.0
+
+    Example:
+
+        from torch.distributed.algorithms.ddp_comm_hooks import (
+            default_hooks as default,
+            powerSGD_hook as powerSGD,
+        )
+
+        # fp16_compress_hook for compress gradients
+        register_ddp_comm_hook(
+            model=ddp_model,
+            ddp_comm_hook=default.fp16_compress_hook,
+        )
+
+        # powerSGD_hook
+        register_ddp_comm_hook(
+            model=ddp_model,
+            ddp_comm_state=powerSGD.PowerSGDState(
+                process_group=None,
+                matrix_approximation_rank=1,
+                start_powerSGD_iter=5000,
+            ),
+            ddp_comm_hook=powerSGD.powerSGD_hook,
+        )
+
+        # fp16_compress_wrapper combined with other communication hook
+        register_ddp_comm_hook(
+            model=ddp_model,
+            ddp_comm_state=powerSGD.PowerSGDState(
+                process_group=None,
+                matrix_approximation_rank=1,
+                start_powerSGD_iter=5000,
+            ),
+            ddp_comm_hook=powerSGD.powerSGD_hook,
+            ddp_comm_wrapper=default.fp16_compress_wrapper,
+        )
+    """
+    if not _TORCH_GREATER_EQUAL_1_8:
+        rank_zero_warn(
+            "Not registering DDP comm hook. "
+            "To use communication hooks, please use pytorch>=1.8.0."
+        )
+        return
+    if ddp_comm_hook is None:
+        return
+    if ddp_comm_wrapper is not None:
+        if not _TORCH_GREATER_EQUAL_1_9:
+            rank_zero_warn(
+                "Not applying DDP comm wrapper. "
+                "To use communication wrapper, please use pytorch>=1.9.0."
+            )
+        else:
+            rank_zero_info(
+                f"DDP comm wrapper is provided, apply {ddp_comm_wrapper.__qualname__}({ddp_comm_hook.__qualname__})."
+            )
+            ddp_comm_hook = ddp_comm_wrapper(ddp_comm_hook)
+
+    rank_zero_debug(f"Registering DDP comm hook: {ddp_comm_hook.__qualname__}.")
+    model.register_comm_hook(
+        state=ddp_comm_state,
+        hook=ddp_comm_hook,
+    )

pytorch_lightning/utilities/imports.py

@@ -69,6 +69,7 @@ def _compare_version(package: str, op, version) -> bool:
 _TORCH_GREATER_EQUAL_1_6 = _compare_version("torch", operator.ge, "1.6.0")
 _TORCH_GREATER_EQUAL_1_7 = _compare_version("torch", operator.ge, "1.7.0")
 _TORCH_GREATER_EQUAL_1_8 = _compare_version("torch", operator.ge, "1.8.0")
+_TORCH_GREATER_EQUAL_1_9 = _compare_version("torch", operator.ge, "1.9.0")
 
 _KINETO_AVAILABLE = torch.profiler.kineto_available() if _TORCH_GREATER_EQUAL_1_8 else False
 _APEX_AVAILABLE = _module_available("apex.amp")

tests/plugins/test_custom_plugin.py

@@ -18,7 +18,6 @@
 
 
 class CustomParallelPlugin(DDPPlugin):
-
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
         # Set to None so it will be overwritten by the accelerator connector.