[Fix] TPU Training Type Plugin

CHANGELOG.md

@@ -200,6 +200,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed torch distributed not available in setup hook for DDP ([#6506](https://github.com/PyTorchLightning/pytorch-lightning/pull/6506))
 
 
+- Fixed TPU Colab hang issue, post training ([#6816](https://github.com/PyTorchLightning/pytorch-lightning/pull/6816))
+
+
 - Enforce an epoch scheduler interval when using SWA ([#6588](https://github.com/PyTorchLightning/pytorch-lightning/pull/6588))
 
 

pytorch_lightning/plugins/training_type/single_tpu.py

@@ -11,15 +11,10 @@
 # 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 os
-from typing import Optional, Union
-
 import torch
 
-from pytorch_lightning.core.lightning import LightningModule
 from pytorch_lightning.plugins.training_type.single_device import SingleDevicePlugin
-from pytorch_lightning.plugins.training_type.utils import on_colab_kaggle
-from pytorch_lightning.utilities import _TPU_AVAILABLE, rank_zero_warn
+from pytorch_lightning.utilities import _TPU_AVAILABLE
 from pytorch_lightning.utilities.apply_func import move_data_to_device
 
 if _TPU_AVAILABLE:
@@ -28,17 +23,22 @@
 
 class SingleTPUPlugin(SingleDevicePlugin):
 
-    def __init__(self, device: Union[torch.device, int]):
-        if isinstance(device, int):
-            device = xm.xla_device(device)
+    def __init__(self, device: int):
+
+        device = xm.xla_device(device)
         super().__init__(device)
 
         self.tpu_local_core_rank = 0
         self.tpu_global_core_rank = 0
 
+    @property
     def on_tpu(self) -> bool:
         return True
 
+    @property
+    def is_distributed(self) -> bool:
+        return False
+
     def model_to_device(self) -> None:
         self.model.to(self.root_device)
 
@@ -49,29 +49,10 @@ def pre_dispatch(self) -> None:
         self.tpu_local_core_rank = xm.get_local_ordinal()
         self.tpu_global_core_rank = xm.get_ordinal()
 
-    def post_dispatch(self) -> None:
-        model = self.lightning_module
-
-        if on_colab_kaggle():
-            rank_zero_warn("cleaning up... please do not interrupt")
-            self.save_spawn_weights(model)
-
-    def save_spawn_weights(self, model: LightningModule) -> Optional[str]:
-        """
-        Dump a temporary checkpoint after ddp ends to get weights out of the process
-        """
-        path = os.path.join(model.trainer.default_root_dir, "__temp_weight_distributed_end.ckpt")
-        model.trainer.save_checkpoint(path)
-        return path
-
     def on_save(self, checkpoint: dict) -> dict:
         """
         Move XLA tensors to CPU before saving
         Recommended on XLA Guide:
         https://github.com/pytorch/xla/blob/master/API_GUIDE.md#saving-and-loading-xla-tensors
         """
         return move_data_to_device(checkpoint, torch.device("cpu"))
-
-    @property
-    def is_distributed(self):
-        return False

pytorch_lightning/plugins/training_type/tpu_spawn.py

@@ -20,9 +20,7 @@
 import torch
 import torch.multiprocessing as mp
 
-from pytorch_lightning.core.lightning import LightningModule
 from pytorch_lightning.plugins.training_type.ddp_spawn import DDPSpawnPlugin
-from pytorch_lightning.plugins.training_type.utils import on_colab_kaggle
 from pytorch_lightning.trainer.states import TrainerState
 from pytorch_lightning.utilities import _OMEGACONF_AVAILABLE, _TPU_AVAILABLE, rank_zero_warn
 from pytorch_lightning.utilities.apply_func import apply_to_collection
@@ -32,28 +30,20 @@
 
 if _TPU_AVAILABLE:
     import torch_xla.core.xla_model as xm
-    import torch_xla.distributed.parallel_loader as xla_pl
     import torch_xla.distributed.xla_multiprocessing as xmp
     from torch_xla.core.xla_model import rendezvous
-    from torch_xla.distributed.parallel_loader import ParallelLoader
+    from torch_xla.distributed.parallel_loader import MpDeviceLoader
 else:
-    xm, xla_pl, xmp, ParallelLoader, rendezvous = [None] * 5
+    xm, xmp, MpDeviceLoader, rendezvous = [None] * 4
 
 if _OMEGACONF_AVAILABLE:
     from omegaconf import DictConfig, ListConfig, OmegaConf
 
 
 class TPUSpawnPlugin(DDPSpawnPlugin):
 
-    def __init__(
-        self,
-        parallel_devices: Optional[List[torch.device]] = None,
-        num_nodes: int = 1,
-        **kwargs: Dict[str, Any]
-    ) -> None:
-        super().__init__(
-            parallel_devices, num_nodes=num_nodes, cluster_environment=None, sync_batchnorm=False, **kwargs
-        )
+    def __init__(self, parallel_devices: Optional[List[int]] = None, **kwargs: Dict[str, Any]) -> None:
+        super().__init__(parallel_devices, num_nodes=1, cluster_environment=None, sync_batchnorm=False)
         self.tpu_local_core_rank = 0
         self.start_method = None
 
@@ -74,10 +64,9 @@ def distributed_sampler_kwargs(self) -> dict:
     def is_distributed(self):
         return self.world_size != 1
 
-    def process_dataloader(self, dataloader: Union[Iterable, torch.utils.data.DataLoader]) -> ParallelLoader:
+    def process_dataloader(self, dataloader: Union[Iterable, torch.utils.data.DataLoader]) -> MpDeviceLoader:
         device = xm.xla_device()
-        dataloader = xla_pl.ParallelLoader(dataloader, [device])
-        dataloader = dataloader.per_device_loader(device)
+        dataloader = MpDeviceLoader(dataloader, device)
         return dataloader
 
     def configure_ddp(self) -> None:
@@ -115,7 +104,6 @@ def new_process(self, process_idx: int, trainer, mp_queue) -> None:
 
         results = trainer.run_stage()
 
-        self.__save_end_of_training_weights(self.lightning_module)
         self.transfer_distrib_spawn_state_on_fit_end(results)
 
         # https://github.com/pytorch/xla/issues/1801#issuecomment-602799542
@@ -125,12 +113,6 @@ def new_process(self, process_idx: int, trainer, mp_queue) -> None:
         if self.global_rank == 0:
             time.sleep(2)
 
-    def __save_end_of_training_weights(self, model: LightningModule) -> None:
-        # when training ends on these platforms dump weights to get out of the main process
-        if on_colab_kaggle():
-            rank_zero_warn("cleaning up... please do not interrupt")
-            self.save_spawn_weights(model)
-
     def model_to_device(self) -> None:
         self._model.to(xm.xla_device())
 
@@ -172,37 +154,7 @@ def broadcast(self, obj: object, src: int = 0) -> object:
         obj = torch.load(buffer)
         return obj
 
-    def load_spawn_weights(self, original_model: LightningModule) -> LightningModule:
-        """
-        Load the temp weights saved in the process
-        To recover the trained model from the ddp process we load the saved weights
-        """
-
-        loaded_model = original_model
-
-        if self.is_global_zero:
-            # load weights saved in ddp
-            path = os.path.join(original_model.trainer.default_root_dir, "__temp_weight_distributed_end.ckpt")
-            loaded_model = original_model.__class__.load_from_checkpoint(path)
-
-            # copy loaded weights to old model
-            original_model.load_state_dict(loaded_model.state_dict())
-
-            # remove ddp weights
-            os.remove(path)
-
-        return loaded_model
-
-    def save_spawn_weights(self, model: LightningModule) -> Optional[str]:
-        """
-        Dump a temporary checkpoint after ddp ends to get weights out of the process
-        """
-        if model.trainer.is_global_zero:
-            path = os.path.join(model.trainer.default_root_dir, "__temp_weight_distributed_end.ckpt")
-            model.trainer.save_checkpoint(path)
-            return path
-
-    def reduce_decision(self, decision: bool) -> bool:
+    def reduce_boolean_decision(self, decision: bool) -> bool:
         decision = torch.tensor(int(decision), device=self.device)
         decision = self.reduce(decision, "sum")
         decision = bool(decision == self.world_size)
@@ -226,39 +178,6 @@ def reduce(self, output, group: Optional[Any] = None, reduce_op: Optional[Union[
 
         return output
 
-    def post_dispatch(self) -> None:
-        # TODO: Check if trainer references can be resolved otherwise
-        model = self.lightning_module
-
-        # restore main state with best weights
-        best_path = self.mp_queue.get()
-        last_path = self.mp_queue.get()
-        self._results = self.mp_queue.get()
-
-        # transfer back the best path to the trainer
-        if self.lightning_module.trainer.checkpoint_callback is not None:
-            self.lightning_module.trainer.checkpoint_callback.best_model_path = best_path
-        # todo, pass also bets score
-
-        # load last weights
-        if last_path and model.trainer.state == TrainerState.FITTING:
-            ckpt = torch.load(last_path, map_location=lambda storage, loc: storage)
-            model.load_state_dict(ckpt)
-
-        self._model = model
-
-        # when training completes, load the weights back in main process
-        self.__load_weights_on_main_process()
-
-    def __load_weights_on_main_process(self) -> None:
-        model = self.lightning_module
-
-        # load weights if not interrupted
-        if on_colab_kaggle() and model.trainer.state == TrainerState.FITTING:
-            self.load_spawn_weights(model)
-
-        self._model = model
-
     def _close_logger(self, trainer) -> None:
         if trainer.logger is not None:
             trainer.logger.finalize("success")

pytorch_lightning/trainer/connectors/accelerator_connector.py

@@ -257,7 +257,7 @@ def use_dp(self) -> bool:
     def use_ddp(self) -> bool:
         return self._distrib_type in (
             DistributedType.DDP, DistributedType.DDP_SPAWN, DistributedType.DDP_SHARDED,
-            DistributedType.DDP_SHARDED_SPAWN, DistributedType.DEEPSPEED
+            DistributedType.DDP_SHARDED_SPAWN, DistributedType.DEEPSPEED, DistributedType.TPU_SPAWN
         )
 
     @property
@@ -297,7 +297,8 @@ def parallel_devices(self) -> List[Union[torch.device, int]]:
         elif self.on_tpu:
             # explicitly don't make a tpu device here!
             # https://github.com/PyTorchLightning/pytorch-lightning/issues/3169
-            devices = [i for i in self.parallel_device_ids]
+            if isinstance(self.tpu_cores, int):
+                devices = list(range(self.tpu_cores))
         else:
             devices = [torch.device("cpu")] * self.num_processes
         return devices
@@ -376,6 +377,7 @@ def select_training_type_plugin(self) -> TrainingTypePlugin:
             use_torchelastic_ddp = self.use_ddp and self.is_using_torchelastic
             use_ddp_spawn = self._distrib_type == DistributedType.DDP_SPAWN
             use_ddp_cpu_spawn = self.use_ddp and self.on_cpu
+            use_tpu_spawn = self.on_tpu and self._distrib_type == DistributedType.TPU_SPAWN
             use_ddp_cpu_torch_elastic = use_ddp_cpu_spawn and self.is_using_torchelastic
             use_ddp_cpu_slurm = use_ddp_cpu_spawn and self.is_slurm_managing_tasks
             use_ddp_sharded = self._distrib_type == DistributedType.DDP_SHARDED
@@ -386,7 +388,7 @@ def select_training_type_plugin(self) -> TrainingTypePlugin:
             if os.environ.get("PL_IN_DDP_SUBPROCESS", False):
                 use_torchelastic_ddp = False
 
-            if self.on_tpu:
+            if use_tpu_spawn:
                 ddp_plugin_cls = TPUSpawnPlugin
             elif use_ddp_sharded:
                 ddp_plugin_cls = DDPShardedPlugin
@@ -409,11 +411,8 @@ def select_training_type_plugin(self) -> TrainingTypePlugin:
             plugin = DataParallelPlugin(parallel_devices=self.parallel_devices)
         elif self.use_horovod:
             plugin = HorovodPlugin(parallel_devices=self.parallel_devices)
-        elif self.on_tpu:
-            if isinstance(self.tpu_cores, list):
-                plugin = SingleTPUPlugin(self.tpu_id)
-            else:
-                plugin = TPUSpawnPlugin(parallel_devices=list(range(self.tpu_cores)))
+        elif self.on_tpu and isinstance(self.tpu_cores, list):
+            plugin = SingleTPUPlugin(self.tpu_id)
         else:
             single_gpu_ordinal = device_parser.determine_root_gpu_device(self.parallel_device_ids)
             plugin = SingleDevicePlugin(device=torch.device(f"cuda:{single_gpu_ordinal}" if self.on_gpu else "cpu"))
@@ -507,6 +506,8 @@ def set_distributed_mode(self, distributed_backend: Optional[str] = None):
         # special case with TPUs
         elif self.distributed_backend == 'tpu' or self.tpu_cores is not None:
             self._device_type = DeviceType.TPU
+            if isinstance(self.tpu_cores, int):
+                self._distrib_type = DistributedType.TPU_SPAWN
         elif self.distributed_backend and self._distrib_type is None:
             self._distrib_type = DistributedType(self.distributed_backend)
 
@@ -515,9 +516,9 @@ def set_distributed_mode(self, distributed_backend: Optional[str] = None):
         if self.num_gpus > 0 and not _on_cpu:
             self._device_type = DeviceType.GPU
 
-        _distrib_types = (DistributedType.DP, DistributedType.DDP, DistributedType.DDP_SPAWN, DistributedType.DDP2)
+        _gpu_distrib_types = (DistributedType.DP, DistributedType.DDP, DistributedType.DDP_SPAWN, DistributedType.DDP2)
         # DP and DDP2 cannot run without GPU
-        if self.num_gpus == 0 and self._distrib_type in _distrib_types and not _on_cpu:
+        if self.num_gpus == 0 and self._distrib_type in _gpu_distrib_types and not _on_cpu:
             rank_zero_warn(
                 'You requested distributed training on GPUs, but none is available, so we set backend to `ddp_cpu`.'
             )

pytorch_lightning/utilities/enums.py

@@ -62,7 +62,9 @@ class DistributedType(LightningEnum):
     @staticmethod
     def interactive_compatible_types() -> List['DistributedType']:
         """Returns a list containing interactive compatible DistributeTypes"""
-        return [DistributedType.DP, DistributedType.DDP_SPAWN, DistributedType.DDP_SHARDED_SPAWN]
+        return [
+            DistributedType.DP, DistributedType.DDP_SPAWN, DistributedType.DDP_SHARDED_SPAWN, DistributedType.TPU_SPAWN
+        ]
 
     def is_interactive_compatible(self) -> bool:
         """Returns whether self is interactive compatible"""
@@ -72,6 +74,7 @@ def is_interactive_compatible(self) -> bool:
     DDP = 'ddp'
     DDP2 = 'ddp2'
     DDP_SPAWN = 'ddp_spawn'
+    TPU_SPAWN = 'tpu_spawn'
     DEEPSPEED = 'deepspeed'
     HOROVOD = 'horovod'
     DDP_SHARDED = 'ddp_sharded'

tests/models/test_tpu.py

@@ -210,8 +210,8 @@ def test_tpu_grad_norm(tmpdir):
         progress_bar_refresh_rate=0,
         max_epochs=4,
         tpu_cores=1,
-        limit_train_batches=4,
-        limit_val_batches=4,
+        limit_train_batches=0.4,
+        limit_val_batches=0.4,
         gradient_clip_val=0.5,
     )