[bugfix] Apex never instantiated.

CHANGELOG.md

@@ -434,6 +434,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `LightningModule.save_hyperparameters()` when attempting to save an empty container ([#7268](https://github.com/PyTorchLightning/pytorch-lightning/pull/7268))
 
 
+- Fixed `apex` not properly instantiated when running with `ddp` ([#7274](https://github.com/PyTorchLightning/pytorch-lightning/pull/7274))
+
 
 ## [1.2.7] - 2021-04-06
 

pytorch_lightning/accelerators/accelerator.py

@@ -107,6 +107,11 @@ def pre_dispatch(self, trainer: 'pl.Trainer') -> None:
             self.setup_optimizers(trainer)
         self.precision_plugin.pre_dispatch()
 
+    def dispatch(self, trainer: 'pl.Trainer') -> None:
+        """Hook to do something before the training/evaluation/prediction starts."""
+        self.training_type_plugin.dispatch(trainer)
+        self.precision_plugin.dispatch(trainer)
+
     def post_dispatch(self, trainer: 'pl.Trainer') -> None:
         """Hook to do something after the training/evaluation/prediction starts."""
         self.training_type_plugin.post_dispatch()

pytorch_lightning/plugins/base_plugin.py

@@ -15,13 +15,18 @@
 from abc import ABC
 from typing import Generator
 
+import pytorch_lightning as pl
+
 
 class Plugin(ABC):
     """Basic class for all precision- and training type plugins."""
 
     def pre_dispatch(self) -> None:
         """Hook to do something before the training/evaluation/prediction starts."""
 
+    def dispatch(self, trainer: "pl.Trainer") -> None:
+        """Hook to do something at trainer run_stage starts."""
+
     def post_dispatch(self) -> None:
         """Hook to do something after the training/evaluation/prediction finishes."""
 

pytorch_lightning/plugins/precision/apex_amp.py

@@ -11,14 +11,14 @@
 # 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, Callable, ContextManager, List, Sequence, Tuple, Type
+from typing import Any, Callable, ContextManager, Sequence
 
 import torch
 from torch import Tensor
-from torch.nn import Module
 from torch.optim import Optimizer
 
-from pytorch_lightning.core import LightningModule
+import pytorch_lightning as pl
+from pytorch_lightning.core.lightning import LightningModule
 from pytorch_lightning.plugins.precision.mixed import MixedPrecisionPlugin
 from pytorch_lightning.utilities import _APEX_AVAILABLE, AMPType
 from pytorch_lightning.utilities.types import _PARAMETERS
@@ -34,24 +34,19 @@ def __init__(self, amp_level: str = "O2") -> None:
         super().__init__()
         self.backend = AMPType.APEX
         self.amp_level = amp_level
+        self._connected = False
 
     def master_params(self, optimizer: Optimizer) -> _PARAMETERS:
         return amp.master_params(optimizer)
 
-    def connect(
-        self,
-        model: Module,
-        optimizers: List[Optimizer],
-        lr_schedulers: List[Any],
-    ) -> Tuple[Module, List[Optimizer], List[Any]]:
-        """Connects the precision plugin to the training process,
-        configures apex and reinits the schedulers
-        """
-        if model.device.type != "cuda":
-            return model, optimizers, lr_schedulers
-        model, optimizers = self.configure_apex(amp, model, list(optimizers), self.amp_level)
-        self.reinit_scheduler_properties(optimizers, lr_schedulers)
-        return model, optimizers, lr_schedulers
+    def dispatch(self, trainer: "pl.Trainer") -> None:
+        if not self._connected:
+            accelerator = trainer.accelerator
+            _, accelerator.optimizers = amp.initialize(
+                trainer.lightning_module, accelerator.optimizers, opt_level=self.amp_level
+            )
+            self._connected = True
+        return super().dispatch(trainer)
 
     def backward(
         self,
@@ -99,40 +94,6 @@ def backward(
         closure_loss = closure_loss.detach()
         return closure_loss
 
-    def configure_apex(
-        self,
-        amp: Type,
-        model: Module,
-        optimizers: List[Optimizer],
-        amp_level: str,
-    ) -> Tuple[Module, List[Optimizer]]:
-        r"""
-        Override to init AMP your own way.
-        Must return a model and list of optimizers.
-
-        Args:
-            amp: pointer to amp library object.
-            model: pointer to current :class:`torch.nn.Module`.
-            optimizers: list of optimizers passed in :meth:`configure_optimizers`.
-            amp_level: AMP mode chosen ('O1', 'O2', etc...)
-
-        Return:
-            Apex wrapped model and optimizers
-
-        Examples:
-            .. code-block:: python
-
-                # Default implementation used by Trainer.
-                def configure_apex(self, amp, model, optimizers, amp_level):
-                    model, optimizers = amp.initialize(
-                        model, optimizers, opt_level=amp_level,
-                    )
-
-                    return model, optimizers
-        """
-        model, optimizers = amp.initialize(model, optimizers, opt_level=amp_level)
-        return model, optimizers
-
     @staticmethod
     def reinit_scheduler_properties(optimizers: Sequence[Optimizer], schedulers: Sequence[Any]) -> None:
         """Reinitializes schedulers with correct properties"""

pytorch_lightning/trainer/trainer.py

@@ -516,7 +516,8 @@ def dispatch(self):
         else:
             self.accelerator.start_training(self)
 
-    def run_stage(self) -> Optional[Union[_EVALUATE_OUTPUT, _PREDICT_OUTPUT]]:
+    def run_stage(self):
+        self.accelerator.dispatch(self)
         self.profile_connector.setup()
 
         if self.evaluating:

tests/plugins/test_amp_plugins.py

@@ -1,3 +1,17 @@
+# Copyright The PyTorch Lightning 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 os
 from unittest import mock
 
@@ -37,7 +51,7 @@ class MyApexPlugin(ApexMixedPrecisionPlugin):
         pytest.param('native', False, NativeMixedPrecisionPlugin, marks=RunIf(amp_native=True)),
         pytest.param('native', True, MyNativeAMP, marks=RunIf(amp_native=True)),
         pytest.param('apex', False, ApexMixedPrecisionPlugin, marks=RunIf(amp_apex=True)),
-        pytest.param('apex', True, MyApexPlugin, marks=RunIf(amp_apex=True))
+        pytest.param('apex', True, MyApexPlugin, marks=RunIf(amp_apex=True)),
     ]
 )
 def test_amp_apex_ddp(
@@ -83,3 +97,47 @@ def test_amp_gradient_unscale(tmpdir, accum: int):
         accumulate_grad_batches=accum,
     )
     trainer.fit(model)
+
+
+@RunIf(min_gpus=2, amp_apex=True, special=True)
+@pytest.mark.parametrize("amp_level", ['O2'])
+def test_amp_apex_ddp_fit(amp_level, tmpdir):
+
+    class CustomBoringModel(BoringModel):
+
+        def training_step(self, batch, batch_idx):
+            assert self.layer.weight.dtype == torch.float16
+            assert self.trainer.precision_plugin._connected
+            return super().training_step(batch, batch_idx)
+
+    trainer = Trainer(
+        default_root_dir=tmpdir,
+        fast_dev_run=True,
+        precision=16,
+        amp_backend="apex",
+        gpus=2,
+        accelerator='ddp',
+        plugins=ApexMixedPrecisionPlugin(amp_level=amp_level),
+    )
+    assert isinstance(trainer.precision_plugin, ApexMixedPrecisionPlugin)
+    model = CustomBoringModel()
+    trainer.fit(model)
+    trainer.test(model)
+
+
+@RunIf(min_gpus=2, amp_apex=True)
+@pytest.mark.parametrize("amp_level", ['O2'])
+def test_amp_apex_ddp_spawn_fit(amp_level, tmpdir):
+
+    trainer = Trainer(
+        default_root_dir=tmpdir,
+        fast_dev_run=True,
+        precision=16,
+        amp_backend="apex",
+        gpus=2,
+        accelerator='ddp_spawn',
+        plugins=ApexMixedPrecisionPlugin(amp_level=amp_level),
+    )
+    assert isinstance(trainer.precision_plugin, ApexMixedPrecisionPlugin)
+    model = BoringModel()
+    trainer.fit(model)

tests/plugins/test_cluster_integration.py

@@ -1,3 +1,16 @@
+# Copyright The PyTorch Lightning 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 os
 from unittest import mock