Refactor: clean trainer device & distrib setters

CHANGELOG.md

@@ -33,6 +33,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
+- Fixed distributed setting and `ddp_cpu` only with `num_processes>1` ([#5297](https://github.com/PyTorchLightning/pytorch-lightning/pull/5297))
+
 
 ## [1.1.0] - 2020-12-09
 

benchmarks/test_sharded_parity.py

@@ -1,7 +1,7 @@
 import os
 import platform
 import time
-from typing import Union
+from typing import Type, Union
 
 import pytest
 import torch
@@ -14,64 +14,48 @@
 from tests.base.boring_model import BoringModel, RandomDataset
 
 
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
-@pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
-def test_ddp_sharded_plugin_correctness_one_device():
-    plugin_parity_test(
-        accelerator='ddp_cpu',
-        max_percent_speed_diff=0.15,  # slower speed due to one CPU doing additional sequential memory saving calls
-        plugin=DDPShardedPlugin(),
-        model_cls=SeedTrainLoaderModel
-    )
-
-
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="requires GPU machine")
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
+@pytest.mark.skipif(platform.system() == "Windows", reason="Distributed training is not supported on Windows")
 @pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
 def test_ddp_sharded_plugin_correctness_one_gpu():
     plugin_parity_test(
         gpus=1,
         accelerator='ddp_spawn',
         plugin=DDPShardedPlugin(),
-        model_cls=SeedTrainLoaderModel
+        model_cls=SeedTrainLoaderModel,
     )
 
 
 @pytest.mark.skipif(not _NATIVE_AMP_AVAILABLE, reason="Requires native AMP")
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="requires GPU machine")
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
+@pytest.mark.skipif(platform.system() == "Windows", reason="Distributed training is not supported on Windows")
 @pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
 def test_ddp_sharded_plugin_correctness_amp_one_gpu():
     plugin_parity_test(
         gpus=1,
         precision=16,
         accelerator='ddp_spawn',
         plugin=DDPShardedPlugin(),
-        model_cls=SeedTrainLoaderModel
+        model_cls=SeedTrainLoaderModel,
     )
 
 
 @pytest.mark.skip(reason="Not a critical test, skip till drone CI performance improves.")
 @pytest.mark.skipif(torch.cuda.device_count() < 2, reason="test requires multi-GPU machine")
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
+@pytest.mark.skipif(platform.system() == "Windows", reason="Distributed training is not supported on Windows")
 @pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
 def test_ddp_sharded_plugin_correctness_multi_gpu():
     plugin_parity_test(
         gpus=2,
         accelerator='ddp_spawn',
         plugin=DDPShardedPlugin(),
         model_cls=SeedTrainLoaderModel,
-        max_percent_speed_diff=0.25
+        max_percent_speed_diff=0.25,
     )
 
 
 @pytest.mark.skipif(not _NATIVE_AMP_AVAILABLE, reason="Requires native AMP")
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
+@pytest.mark.skipif(platform.system() == "Windows", reason="Distributed training is not supported on Windows")
 @pytest.mark.skipif(torch.cuda.device_count() < 2, reason="test requires multi-GPU machine")
 @pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
 def test_ddp_sharded_plugin_correctness_amp_multi_gpu():
@@ -81,13 +65,12 @@ def test_ddp_sharded_plugin_correctness_amp_multi_gpu():
         accelerator='ddp_spawn',
         plugin=DDPShardedPlugin(),
         model_cls=SeedTrainLoaderModel,
-        max_percent_speed_diff=0.25
+        max_percent_speed_diff=0.25,
     )
 
 
 @pytest.mark.skipif(not _NATIVE_AMP_AVAILABLE, reason="Requires native AMP")
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
+@pytest.mark.skipif(platform.system() == "Windows", reason="Distributed training is not supported on Windows")
 @pytest.mark.skipif(torch.cuda.device_count() < 2, reason="test requires multi-GPU machine")
 @pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
 def test_ddp_string_sharded_plugin_correctness_amp_multi_gpu():
@@ -97,7 +80,7 @@ def test_ddp_string_sharded_plugin_correctness_amp_multi_gpu():
         accelerator='ddp_spawn',
         plugin='ddp_sharded',
         model_cls=SeedTrainLoaderModel,
-        max_percent_speed_diff=0.25
+        max_percent_speed_diff=0.25,
     )
 
 
@@ -133,8 +116,7 @@ def test_ddp_sharded_plugin_correctness_amp_multi_gpu_ddp(tmpdir, args=None):
 
 @pytest.mark.skip(reason="Current issue with multiple optimizers and FairScale.")
 @pytest.mark.skipif(torch.cuda.device_count() < 2, reason="test requires multi-GPU machine")
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
+@pytest.mark.skipif(platform.system() == "Windows", reason="Distributed training is not supported on Windows")
 @pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
 def test_ddp_sharded_plugin_correctness_multi_gpu_multi_optim():
     """
@@ -145,14 +127,13 @@ def test_ddp_sharded_plugin_correctness_multi_gpu_multi_optim():
         gpus=2,
         accelerator='ddp_spawn',
         model_cls=SeedTrainLoaderMultipleOptimizersModel,
-        max_percent_speed_diff=0.25  # Increase speed diff since only 2 GPUs sharding 2 optimizers
+        max_percent_speed_diff=0.25,  # Increase speed diff since only 2 GPUs sharding 2 optimizers
     )
 
 
 @pytest.mark.skip(reason="Current issue with multiple optimizers and FairScale.")
 @pytest.mark.skipif(torch.cuda.device_count() < 2, reason="test requires multi-GPU machine")
-@pytest.mark.skipif(platform.system() == "Windows",
-                    reason="Distributed training is not supported on Windows")
+@pytest.mark.skipif(platform.system() == "Windows", reason="Distributed training is not supported on Windows")
 @pytest.mark.skipif(not _FAIRSCALE_AVAILABLE, reason="Fairscale is not available")
 def test_ddp_sharded_plugin_correctness_multi_gpu_multi_optim_manual(tmpdir):
     """
@@ -163,7 +144,7 @@ def test_ddp_sharded_plugin_correctness_multi_gpu_multi_optim_manual(tmpdir):
         gpus=2,
         accelerator='ddp_spawn',
         model_cls=SeedTrainLoaderManualModel,
-        max_percent_speed_diff=0.25  # Increase speed diff since only 2 GPUs sharding 2 optimizers
+        max_percent_speed_diff=0.25,  # Increase speed diff since only 2 GPUs sharding 2 optimizers
     )
 
 
@@ -259,13 +240,14 @@ def record_ddp_fit_model_stats(trainer, model, use_cuda):
 
 
 def plugin_parity_test(
-        model_cls: SeedTrainLoaderModel,
+        model_cls: Type[SeedTrainLoaderModel],
         plugin: Union[str, DDPPlugin],
         seed: int = 42,
         accelerator: str = 'ddp_spawn',
         gpus: int = 0,
         precision: int = 32,
-        max_percent_speed_diff: float = 0.1):
+        max_percent_speed_diff: float = 0.1,
+):
     """
     Ensures that the trained model is identical to the standard DDP implementation.
     Also checks for speed/memory regressions, we should expect always less memory but performance to fluctuate.

pytorch_lightning/accelerators/accelerator_connector.py

@@ -15,7 +15,7 @@
 
 import torch
 
-from pytorch_lightning.utilities import _HOROVOD_AVAILABLE
+from pytorch_lightning.utilities import _HOROVOD_AVAILABLE, DeviceType, DistributedType
 from pytorch_lightning import _logger as log
 from pytorch_lightning import accelerators
 from pytorch_lightning.accelerators.accelerator import Accelerator
@@ -81,10 +81,7 @@ def on_trainer_init(
         # sync-bn backend
         self.trainer.sync_batchnorm = sync_batchnorm
 
-        self.trainer.tpu_cores = device_parser.parse_tpu_cores(tpu_cores)
-        self.trainer.on_tpu = self.trainer.tpu_cores is not None
-
-        self.trainer.tpu_id = self.trainer.tpu_cores[0] if isinstance(self.trainer.tpu_cores, list) else None
+        self._parse_tpu_device_details(tpu_cores)
 
         if num_processes != 1 and distributed_backend != "ddp_cpu":
             rank_zero_warn("num_processes is only used for `accelerator='ddp_cpu'`. Ignoring it.")
@@ -100,23 +97,10 @@ def on_trainer_init(
 
         self.trainer.data_parallel_device_ids = device_parser.parse_gpu_ids(self.trainer.gpus)
         self.trainer.root_gpu = device_parser.determine_root_gpu_device(self.trainer.data_parallel_device_ids)
-        self.trainer.root_device = torch.device("cpu")
-
-        self.trainer.on_gpu = True if (self.trainer.data_parallel_device_ids and torch.cuda.is_available()) else False
-
-        # tpu state flags
-        self.trainer.use_tpu = False
-        self.trainer.tpu_local_core_rank = None
-        self.trainer.tpu_global_core_rank = None
 
         # distributed backend choice
         self.set_distributed_mode()
 
-        # override dist backend when using tpus
-        if self.trainer.on_tpu:
-            self.trainer.distributed_backend = "tpu"
-            self.trainer.use_tpu = True
-
         # init flags for SLURM+DDP to work
         self.trainer.world_size = 1
         self.trainer.interactive_ddp_procs = []
@@ -135,10 +119,29 @@ def on_trainer_init(
 
         self.trainer.replace_sampler_ddp = replace_sampler_ddp
 
+    def _parse_tpu_device_details(self, tpu_cores):
+        self.trainer.tpu_cores = device_parser.parse_tpu_cores(tpu_cores)
+        if self.trainer.tpu_cores is not None:
+            if _TPU_AVAILABLE:
+                self.trainer._device_type = DeviceType.TPU
+                self.trainer.distributed_backend = "tpu"
+            else:
+                raise MisconfigurationException(
+                    f"You have requested {self.trainer.tpu_cores} TPU cores but none is available."
+                )
+
+        self.trainer.tpu_id = self.trainer.tpu_cores[0] if isinstance(self.trainer.tpu_cores, list) else None
+
+        # tpu state flags
+        self.trainer.tpu_local_core_rank = None
+        self.trainer.tpu_global_core_rank = None
+
     def _map_deprecated_dist_backend(self, accelerator, distributed_backend):
         if distributed_backend is not None:
-            rank_zero_warn(DeprecationWarning('distributed_backend has been renamed to accelerator. '
-                                              'Deprecated in 1.0.0, will be removed in 1.2.0'))
+            rank_zero_warn(
+                '`distributed_backend` has been renamed to accelerator. Deprecated in 1.0.0, will be removed in 1.2.0',
+                DeprecationWarning
+            )
 
         # temporary mapping until we remove all the distributed_backend references
         if accelerator is not None:
@@ -276,71 +279,75 @@ def select_accelerator(self):
             accelerator_backend = accelerators.CPUAccelerator(self.trainer, cluster_env)
         else:
             raise MisconfigurationException(
-                f'Trainer(accelerator={self.trainer.distributed_backend} is not a supported backend'
+                f'`Trainer(accelerator={self.trainer.distributed_backend}, num_nodes={self.trainer.num_nodes},'
+                f' num_processes={self.trainer.num_processes}, ...)` is not a supported backend for'
+                f' num_gpus={self.trainer.num_gpus}'
             )
 
         return accelerator_backend
 
     def set_distributed_mode(self):
-        self.trainer.use_dp = False
-        self.trainer.use_ddp = False
-        self.trainer.use_ddp2 = False
-        self.trainer.use_horovod = False
-        self.trainer.use_single_gpu = False
 
         if self.trainer.distributed_backend is None:
             if self.has_horovodrun():
                 self._set_horovod_backend()
-            elif self.trainer.num_gpus == 0:
-                if self.trainer.num_nodes > 1 or self.trainer.num_processes > 1:
-                    self.trainer.use_ddp = True  # ddp_cpu
-            elif self.trainer.num_gpus == 1:
-                self.trainer.use_single_gpu = True
+            elif self.trainer.num_gpus == 0 and (self.trainer.num_nodes > 1 or self.trainer.num_processes > 1):
+                self.trainer._distrib_type = DistributedType.DDP
             elif self.trainer.num_gpus > 1:
                 rank_zero_warn(
                     'You requested multiple GPUs but did not specify a backend, e.g.'
-                    ' `Trainer(accelerator="dp"|"ddp"|"ddp2")`.'
-                    ' Setting `accelerator="ddp_spawn"` for you.'
+                    ' `Trainer(accelerator="dp"|"ddp"|"ddp2")`. Setting `accelerator="ddp_spawn"` for you.'
                 )
                 self.trainer.distributed_backend = "ddp_spawn"
 
-        if self.trainer.distributed_backend == "dp":
-            # do nothing if num_gpus == 0
-            if self.trainer.num_gpus == 1:
-                self.trainer.use_single_gpu = True
-                self.trainer.use_dp = True
-            elif self.trainer.num_gpus > 1:
-                self.trainer.use_dp = True
-
-        elif self.trainer.distributed_backend in ("ddp", "ddp_spawn"):
-            if self.trainer.num_gpus == 0:
-                if self.trainer.num_nodes > 1 or self.trainer.num_processes > 1:
-                    self.trainer.use_ddp = True  # ddp_cpu
-            elif self.trainer.num_gpus == 1:
-                self.trainer.use_single_gpu = True
-                self.trainer.use_ddp = True
-            elif self.trainer.num_gpus > 1:
-                self.trainer.use_ddp = True
-                self.trainer.num_processes = self.trainer.num_gpus
-
-        elif self.trainer.distributed_backend == "ddp2":
-            # do nothing if num_gpus == 0
-            if self.trainer.num_gpus >= 1:
-                self.trainer.use_ddp2 = True
-        elif self.trainer.distributed_backend == "ddp_cpu":
+        # special case with DDP on CPUs
+        if self.trainer.distributed_backend == "ddp_cpu":
+            self.trainer._distrib_type = DistributedType.DDP
+            self.trainer.data_parallel_device_ids = None
             if self.trainer.num_gpus > 0:
                 rank_zero_warn(
                     'You requested one or more GPUs, but set the backend to `ddp_cpu`. Training will not use GPUs.'
                 )
-            self.trainer.use_ddp = True
-            self.trainer.data_parallel_device_ids = None
-            self.trainer.on_gpu = False
-            self.trainer.on_cpu = True
-        elif self.trainer.distributed_backend == "horovod":
+            if self.trainer.num_processes is None:
+                # define the max CPU available
+                self.trainer.num_processes = os.cpu_count()
+        # special case with TPUs
+        elif self.trainer.distributed_backend == 'tpu':
+            self.trainer._device_type = DeviceType.TPU
+        # set all other requested distrib. types adn if it was not set in the
+        elif self.trainer.distributed_backend and self.trainer._distrib_type is None:
+            self.trainer._distrib_type = DistributedType(self.trainer.distributed_backend)
+
+        # unless you request explicitly for CPU and some GPU are available use them
+        _on_cpu = self.trainer.distributed_backend and 'cpu' in self.trainer.distributed_backend
+        if (self.trainer.num_gpus > 0 and not _on_cpu):
+            self.trainer._device_type = DeviceType.GPU
+
+        _distrib_types = (DistributedType.DP, DistributedType.DDP, DistributedType.DDP_SPAWN, DistributedType.DDP2)
+        # DP and DDP2 cannot run without GPU
+        if (self.trainer.num_gpus == 0 and self.trainer._distrib_type in _distrib_types):
+            rank_zero_warn(
+                'You requested distributed training on GPUs, but none is available, so we set backend to `ddp_cpu`.'
+            )
+            # todo: in some cases it yield in comarison None and int
+            if ((self.trainer.num_nodes and self.trainer.num_nodes > 1)
+                    or (self.trainer.num_processes and self.trainer.num_processes > 1)):
+                self.trainer._distrib_type = DistributedType.DDP
+            else:
+                rank_zero_warn('You are running on single node with no parallelization, so distributed has no effect.')
+                self.trainer._distrib_type = None
+
+        # for DDP overwrite nb processes by requested GPUs
+        if (self.trainer._device_type == DeviceType.GPU
+                and self.trainer._distrib_type in (DistributedType.DDP, DistributedType.DDP_SPAWN)):
+            self.trainer.num_processes = self.trainer.num_gpus
+
+        # Horovod si an extra case...
+        if self.trainer.distributed_backend == "horovod":
             self._set_horovod_backend()
 
         # throw error to force user ddp or ddp2 choice
-        if self.trainer.num_nodes > 1 and not (self.trainer.use_ddp2 or self.trainer.use_ddp):
+        if self.trainer.num_nodes > 1 and self.trainer._distrib_type not in (DistributedType.DDP2, DistributedType.DDP):
             raise MisconfigurationException(
                 'DataParallel does not support num_nodes > 1. Switching to DistributedDataParallel for you. '
                 'To silence this warning set `accelerator="ddp"` or `accelerator="ddp2"`'
@@ -350,20 +357,20 @@ def set_distributed_mode(self):
         num_cores = self.trainer.tpu_cores if self.trainer.tpu_cores is not None else 0
         rank_zero_info(f'TPU available: {_TPU_AVAILABLE}, using: {num_cores} TPU cores')
 
-        if torch.cuda.is_available() and not self.trainer.on_gpu:
+        if torch.cuda.is_available() and self.trainer._device_type != DeviceType.GPU:
             rank_zero_warn('GPU available but not used. Set the --gpus flag when calling the script.')
 
     def _set_horovod_backend(self):
-        self.check_horovod()
-        self.trainer.use_horovod = True
+        self._check_horovod()
+        self.trainer._distrib_type = DistributedType.HOROVOD
 
         # Initialize Horovod to get rank / size info
         hvd.init()
         if self.trainer.on_gpu:
             # Horovod assigns one local GPU per process
             self.trainer.root_gpu = hvd.local_rank()
 
-    def check_horovod(self):
+    def _check_horovod(self):
         """Raises a `MisconfigurationException` if the Trainer is not configured correctly for Horovod."""
         if not _HOROVOD_AVAILABLE:
             raise MisconfigurationException(

pytorch_lightning/plugins/plugin_connector.py

@@ -31,8 +31,6 @@ def __init__(self, trainer):
         self.plugins = []
         self.ddp_plugin = DDPPlugin()
         self.cloud_environment = None
-        self.amp_plugin = NativeAMPPlugin(trainer)
-        self.apex_plugin = ApexPlugin(trainer)
 
     def on_trainer_init(self, plugins: Optional[Union[str, list]]):
         self.plugins = plugins