Add support for pluggable Accelerators

CHANGELOG.md

@@ -137,6 +137,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added `estimated_stepping_batches` property to `Trainer` ([#11599](https://github.com/PyTorchLightning/pytorch-lightning/pull/11599))
 
 
+- Added support for pluggable Accelerators ([#12030](https://github.com/PyTorchLightning/pytorch-lightning/pull/12030))
+
+
 ### Changed
 
 - Make `benchmark` flag optional and set its value based on the deterministic flag ([#11944](https://github.com/PyTorchLightning/pytorch-lightning/pull/11944))

docs/source/extensions/accelerator.rst

@@ -20,6 +20,7 @@ Each Accelerator gets two plugins upon initialization:
 One to handle differences from the training routine and one to handle different precisions.
 
 .. testcode::
+    :skipif: torch.cuda.device_count() < 2
 
     from pytorch_lightning import Trainer
     from pytorch_lightning.accelerators import GPUAccelerator
@@ -28,8 +29,8 @@ One to handle differences from the training routine and one to handle different
 
     accelerator = GPUAccelerator()
     precision_plugin = NativeMixedPrecisionPlugin(precision=16, device="cuda")
-    training_type_plugin = DDPStrategy(accelerator=accelerator, precision_plugin=precision_plugin)
-    trainer = Trainer(strategy=training_type_plugin)
+    training_strategy = DDPStrategy(accelerator=accelerator, precision_plugin=precision_plugin)
+    trainer = Trainer(strategy=training_strategy, devices=2)
 
 
 We expose Accelerators and Plugins mainly for expert users who want to extend Lightning to work with new

pytorch_lightning/accelerators/accelerator.py

@@ -55,6 +55,16 @@ def get_device_stats(self, device: Union[str, torch.device]) -> Dict[str, Any]:
         """
         raise NotImplementedError
 
+    @staticmethod
+    @abstractmethod
+    def parse_devices(devices: Any) -> Any:
+        """Accelerator device parsing logic."""
+
+    @staticmethod
+    @abstractmethod
+    def get_parallel_devices(devices: Any) -> Any:
+        """Gets parallel devices for the Accelerator."""
+
     @staticmethod
     @abstractmethod
     def auto_device_count() -> int:

pytorch_lightning/accelerators/cpu.py

@@ -11,14 +11,13 @@
 # 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.
-from __future__ import annotations
-
-from typing import Any
+from typing import Any, Dict, List, Union
 
 import torch
 
 from pytorch_lightning.accelerators.accelerator import Accelerator
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
+from pytorch_lightning.utilities.rank_zero import rank_zero_warn
 from pytorch_lightning.utilities.types import _DEVICE
 
 
@@ -35,10 +34,25 @@ def setup_environment(self, root_device: torch.device) -> None:
         if root_device.type != "cpu":
             raise MisconfigurationException(f"Device should be CPU, got {root_device} instead.")
 
-    def get_device_stats(self, device: _DEVICE) -> dict[str, Any]:
+    def get_device_stats(self, device: _DEVICE) -> Dict[str, Any]:
         """CPU device stats aren't supported yet."""
         return {}
 
+    @staticmethod
+    def parse_devices(devices: Union[int, str, List[int]]) -> Union[int, str, List[int]]:
+        """Accelerator device parsing logic."""
+        return devices
+
+    @staticmethod
+    def get_parallel_devices(devices: Union[int, str, List[int]]) -> List[torch.device]:
+        """Gets parallel devices for the Accelerator."""
+        if isinstance(devices, int):
+            return [torch.device("cpu")] * devices
+        rank_zero_warn(
+            f"The flag `devices` must be an int with `accelerator='cpu'`, got `devices={devices!r}` instead."
+        )
+        return []
+
     @staticmethod
     def auto_device_count() -> int:
         """Get the devices when set to auto."""

pytorch_lightning/accelerators/gpu.py

@@ -11,18 +11,17 @@
 # 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.
-from __future__ import annotations
-
 import logging
 import os
 import shutil
 import subprocess
-from typing import Any
+from typing import Any, Dict, List, Optional, Union
 
 import torch
 
 import pytorch_lightning as pl
 from pytorch_lightning.accelerators.accelerator import Accelerator
+from pytorch_lightning.utilities import device_parser
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.imports import _TORCH_GREATER_EQUAL_1_8
 from pytorch_lightning.utilities.types import _DEVICE
@@ -44,7 +43,7 @@ def setup_environment(self, root_device: torch.device) -> None:
             raise MisconfigurationException(f"Device should be GPU, got {root_device} instead")
         torch.cuda.set_device(root_device)
 
-    def setup(self, trainer: pl.Trainer) -> None:
+    def setup(self, trainer: "pl.Trainer") -> None:
         # TODO refactor input from trainer to local_rank @four4fish
         self.set_nvidia_flags(trainer.local_rank)
         # clear cache before training
@@ -58,7 +57,7 @@ def set_nvidia_flags(local_rank: int) -> None:
         devices = os.getenv("CUDA_VISIBLE_DEVICES", all_gpu_ids)
         _log.info(f"LOCAL_RANK: {local_rank} - CUDA_VISIBLE_DEVICES: [{devices}]")
 
-    def get_device_stats(self, device: _DEVICE) -> dict[str, Any]:
+    def get_device_stats(self, device: _DEVICE) -> Dict[str, Any]:
         """Gets stats for the given GPU device.
 
         Args:
@@ -75,6 +74,16 @@ def get_device_stats(self, device: _DEVICE) -> dict[str, Any]:
             return torch.cuda.memory_stats(device)
         return get_nvidia_gpu_stats(device)
 
+    @staticmethod
+    def parse_devices(devices: Union[int, str, List[int]]) -> Optional[List[int]]:
+        """Accelerator device parsing logic."""
+        return device_parser.parse_gpu_ids(devices)
+
+    @staticmethod
+    def get_parallel_devices(devices: List[int]) -> List[torch.device]:
+        """Gets parallel devices for the Accelerator."""
+        return [torch.device("cuda", i) for i in devices]
+
     @staticmethod
     def auto_device_count() -> int:
         """Get the devices when set to auto."""
@@ -85,7 +94,7 @@ def is_available() -> bool:
         return torch.cuda.device_count() > 0
 
 
-def get_nvidia_gpu_stats(device: _DEVICE) -> dict[str, float]:
+def get_nvidia_gpu_stats(device: _DEVICE) -> Dict[str, float]:
     """Get GPU stats including memory, fan speed, and temperature from nvidia-smi.
 
     Args:

pytorch_lightning/accelerators/ipu.py

@@ -11,7 +11,7 @@
 # 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.
-from typing import Any, Dict, Union
+from typing import Any, Dict, List, Union
 
 import torch
 
@@ -26,6 +26,16 @@ def get_device_stats(self, device: Union[str, torch.device]) -> Dict[str, Any]:
         """IPU device stats aren't supported yet."""
         return {}
 
+    @staticmethod
+    def parse_devices(devices: int) -> int:
+        """Accelerator device parsing logic."""
+        return devices
+
+    @staticmethod
+    def get_parallel_devices(devices: int) -> List[int]:
+        """Gets parallel devices for the Accelerator."""
+        return list(range(devices))
+
     @staticmethod
     def auto_device_count() -> int:
         """Get the devices when set to auto."""

pytorch_lightning/accelerators/tpu.py

@@ -11,11 +11,12 @@
 # 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.
-from typing import Any, Dict, Union
+from typing import Any, Dict, List, Optional, Union
 
 import torch
 
 from pytorch_lightning.accelerators.accelerator import Accelerator
+from pytorch_lightning.utilities import device_parser
 from pytorch_lightning.utilities.imports import _TPU_AVAILABLE, _XLA_AVAILABLE
 
 if _XLA_AVAILABLE:
@@ -43,6 +44,18 @@ def get_device_stats(self, device: Union[str, torch.device]) -> Dict[str, Any]:
         }
         return device_stats
 
+    @staticmethod
+    def parse_devices(devices: Union[int, str, List[int]]) -> Optional[Union[int, List[int]]]:
+        """Accelerator device parsing logic."""
+        return device_parser.parse_tpu_cores(devices)
+
+    @staticmethod
+    def get_parallel_devices(devices: Union[int, List[int]]) -> List[int]:
+        """Gets parallel devices for the Accelerator."""
+        if isinstance(devices, int):
+            return list(range(devices))
+        return devices
+
     @staticmethod
     def auto_device_count() -> int:
         """Get the devices when set to auto."""

pytorch_lightning/trainer/connectors/accelerator_connector.py

@@ -168,6 +168,7 @@ def __init__(
         self._precision_flag: Optional[Union[int, str]] = None
         self._precision_plugin_flag: Optional[PrecisionPlugin] = None
         self._cluster_environment_flag: Optional[Union[ClusterEnvironment, str]] = None
+        self._parallel_devices: List[Union[int, torch.device]] = []
         self.checkpoint_io: Optional[CheckpointIO] = None
         self._amp_type_flag: Optional[LightningEnum] = None
         self._amp_level_flag: Optional[str] = amp_level
@@ -361,6 +362,7 @@ def _check_config_and_set_final_flags(
                         self._accelerator_flag = "cpu"
                     if self._strategy_flag.parallel_devices[0].type == "cuda":
                         self._accelerator_flag = "gpu"
+                    self._parallel_devices = self._strategy_flag.parallel_devices
 
         amp_type = amp_type if isinstance(amp_type, str) else None
         self._amp_type_flag = AMPType.from_str(amp_type)
@@ -387,7 +389,7 @@ def _check_device_config_and_set_final_flags(
             devices, num_processes, gpus, ipus, tpu_cores
         )
 
-        if self._devices_flag in ([], 0, "0", "0,"):
+        if self._devices_flag in ([], 0, "0"):
             rank_zero_warn(f"You passed `devices={devices}`, switching to `cpu` accelerator")
             self._accelerator_flag = "cpu"
 
@@ -408,10 +410,8 @@ def _map_deprecated_devices_specfic_info_to_accelerator_and_device_flag(
         """Sets the `devices_flag` and `accelerator_flag` based on num_processes, gpus, ipus, tpu_cores."""
         self._gpus: Optional[Union[List[int], str, int]] = gpus
         self._tpu_cores: Optional[Union[List[int], str, int]] = tpu_cores
-        gpus = device_parser.parse_gpu_ids(gpus)
-        tpu_cores = device_parser.parse_tpu_cores(tpu_cores)
         deprecated_devices_specific_flag = num_processes or gpus or ipus or tpu_cores
-        if deprecated_devices_specific_flag and deprecated_devices_specific_flag not in (0, "0"):
+        if deprecated_devices_specific_flag and deprecated_devices_specific_flag not in ([], 0, "0"):
             if devices:
                 # TODO: @awaelchli improve error message
                 rank_zero_warn(
@@ -456,51 +456,34 @@ def _choose_accelerator(self) -> str:
 
     def _set_parallel_devices_and_init_accelerator(self) -> None:
         # TODO add device availability check
-        self._parallel_devices: List[Union[int, torch.device]] = []
-
         if isinstance(self._accelerator_flag, Accelerator):
             self.accelerator: Accelerator = self._accelerator_flag
-        elif self._accelerator_flag == "tpu":
-            self.accelerator = TPUAccelerator()
-            self._set_devices_flag_if_auto_passed()
-            if isinstance(self._devices_flag, int):
-                self._parallel_devices = list(range(self._devices_flag))
-            else:
-                self._parallel_devices = self._devices_flag  # type: ignore[assignment]
-
-        elif self._accelerator_flag == "ipu":
-            self.accelerator = IPUAccelerator()
-            self._set_devices_flag_if_auto_passed()
-            if isinstance(self._devices_flag, int):
-                self._parallel_devices = list(range(self._devices_flag))
-
-        elif self._accelerator_flag == "gpu":
-            self.accelerator = GPUAccelerator()
-            self._set_devices_flag_if_auto_passed()
-            if isinstance(self._devices_flag, int) or isinstance(self._devices_flag, str):
-                self._devices_flag = int(self._devices_flag)
-                self._parallel_devices = (
-                    [torch.device("cuda", i) for i in device_parser.parse_gpu_ids(self._devices_flag)]  # type: ignore
-                    if self._devices_flag != 0
-                    else []
+        else:
+            ACCELERATORS = {
+                "cpu": CPUAccelerator,
+                "gpu": GPUAccelerator,
+                "tpu": TPUAccelerator,
+                "ipu": IPUAccelerator,
+            }
+            assert self._accelerator_flag is not None
+            self._accelerator_flag = self._accelerator_flag.lower()
+            if self._accelerator_flag not in ACCELERATORS:
+                raise MisconfigurationException(
+                    "When passing string value for the `accelerator` argument of `Trainer`,"
+                    f" it can only be one of {list(ACCELERATORS)}."
                 )
-            else:
-                self._parallel_devices = [torch.device("cuda", i) for i in self._devices_flag]  # type: ignore
+            accelerator_class = ACCELERATORS[self._accelerator_flag]
+            self.accelerator = accelerator_class()  # type: ignore[abstract]
 
-        elif self._accelerator_flag == "cpu":
-            self.accelerator = CPUAccelerator()
-            self._set_devices_flag_if_auto_passed()
-            if isinstance(self._devices_flag, int):
-                self._parallel_devices = [torch.device("cpu")] * self._devices_flag
-            else:
-                rank_zero_warn(
-                    "The flag `devices` must be an int with `accelerator='cpu'`,"
-                    f" got `devices={self._devices_flag}` instead."
-                )
+        self._set_devices_flag_if_auto_passed()
 
         self._gpus = self._devices_flag if not self._gpus else self._gpus
         self._tpu_cores = self._devices_flag if not self._tpu_cores else self._tpu_cores
 
+        self._devices_flag = self.accelerator.parse_devices(self._devices_flag)
+        if not self._parallel_devices:
+            self._parallel_devices = self.accelerator.get_parallel_devices(self._devices_flag)
+
     def _set_devices_flag_if_auto_passed(self) -> None:
         if self._devices_flag == "auto" or not self._devices_flag:
             self._devices_flag = self.accelerator.auto_device_count()

pytorch_lightning/trainer/connectors/data_connector.py

@@ -21,7 +21,7 @@
 from torch.utils.data.distributed import DistributedSampler
 
 import pytorch_lightning as pl
-from pytorch_lightning.accelerators import IPUAccelerator
+from pytorch_lightning.accelerators.ipu import IPUAccelerator
 from pytorch_lightning.overrides.distributed import UnrepeatedDistributedSampler
 from pytorch_lightning.strategies import DDPSpawnStrategy
 from pytorch_lightning.trainer.states import RunningStage, TrainerFn

tests/accelerators/test_accelerator_connector.py

@@ -341,6 +341,14 @@ def creates_processes_externally(self) -> bool:
 @mock.patch("pytorch_lightning.strategies.DDPStrategy.setup_distributed", autospec=True)
 def test_custom_accelerator(device_count_mock, setup_distributed_mock):
     class Accel(Accelerator):
+        @staticmethod
+        def parse_devices(devices):
+            return devices
+
+        @staticmethod
+        def get_parallel_devices(devices):
+            return [torch.device("cpu")] * devices
+
         @staticmethod
         def auto_device_count() -> int:
             return 1
@@ -413,10 +421,17 @@ def test_ipython_incompatible_backend_error(_, monkeypatch):
         Trainer(strategy="dp")
 
 
-@pytest.mark.parametrize("trainer_kwargs", [{}, dict(strategy="dp", accelerator="gpu"), dict(accelerator="tpu")])
-def test_ipython_compatible_backend(trainer_kwargs, monkeypatch):
+@mock.patch("torch.cuda.device_count", return_value=2)
+def test_ipython_compatible_dp_strategy_gpu(_, monkeypatch):
+    monkeypatch.setattr(pytorch_lightning.utilities, "_IS_INTERACTIVE", True)
+    trainer = Trainer(strategy="dp", accelerator="gpu")
+    assert trainer.strategy.launcher is None or trainer.strategy.launcher.is_interactive_compatible
+
+
+@mock.patch("pytorch_lightning.accelerators.tpu.TPUAccelerator.parse_devices", return_value=8)
+def test_ipython_compatible_strategy_tpu(_, monkeypatch):
     monkeypatch.setattr(pytorch_lightning.utilities, "_IS_INTERACTIVE", True)
-    trainer = Trainer(**trainer_kwargs)
+    trainer = Trainer(accelerator="tpu")
     assert trainer.strategy.launcher is None or trainer.strategy.launcher.is_interactive_compatible
 
 
@@ -883,10 +898,9 @@ def test_strategy_choice_ddp_cpu_slurm(device_count_mock, setup_distributed_mock
     assert trainer.strategy.local_rank == 0
 
 
-def test_unsupported_tpu_choice(monkeypatch):
-    import pytorch_lightning.utilities.imports as imports
+@mock.patch("pytorch_lightning.accelerators.tpu.TPUAccelerator.parse_devices", return_value=8)
+def test_unsupported_tpu_choice(mock_devices):
 
-    monkeypatch.setattr(imports, "_XLA_AVAILABLE", True)
     with pytest.raises(MisconfigurationException, match=r"accelerator='tpu', precision=64\)` is not implemented"):
         Trainer(accelerator="tpu", precision=64)