feat: support tensor parallel using Pytorch 2.0

Signed-off-by: Mehant Kammakomati <[email protected]>

Author: kmehant

src/accelerate/accelerator.py

@@ -67,6 +67,7 @@
     ProjectConfiguration,
     RNGType,
     TorchDynamoPlugin,
+    TorchTensorParallelPlugin,
     apply_fp8_autowrap,
     check_os_kernel,
     clean_state_dict_for_safetensors,
@@ -188,6 +189,9 @@ class Accelerator:
         fsdp_plugin ([`~utils.FullyShardedDataParallelPlugin`], *optional*):
             Tweak your FSDP related args using this argument. This argument is optional and can be configured directly
             using *accelerate config*
+        torch_tp_plugin ([`~utils.TorchTensorParallelPlugin`], *optional*):
+            Tweak your torch tensor parallel. This argument is optional and can be configured directly using
+            *accelerate config*
         megatron_lm_plugin ([`~utils.MegatronLMPlugin`], *optional*):
             Tweak your MegatronLM related args using this argument. This argument is optional and can be configured
             directly using *accelerate config*
@@ -254,6 +258,7 @@ def __init__(
         dataloader_config: DataLoaderConfiguration | None = None,
         deepspeed_plugin: DeepSpeedPlugin | dict[str, DeepSpeedPlugin] | None = None,
         fsdp_plugin: FullyShardedDataParallelPlugin | None = None,
+        torch_tp_plugin: TorchTensorParallelPlugin | None = None,
         megatron_lm_plugin: MegatronLMPlugin | None = None,
         rng_types: list[str | RNGType] | None = None,
         log_with: str | LoggerType | GeneralTracker | list[str | LoggerType | GeneralTracker] | None = None,
@@ -418,6 +423,7 @@ def __init__(
             dynamo_plugin=dynamo_plugin,
             deepspeed_plugin=deepspeed_plugins,
             fsdp_plugin=fsdp_plugin,
+            torch_tp_plugin=torch_tp_plugin,
             megatron_lm_plugin=megatron_lm_plugin,
             _from_accelerator=True,
             **kwargs,
@@ -1461,6 +1467,8 @@ def prepare_model(self, model: torch.nn.Module, device_placement: bool = None, e
                     )
                     if self.ddp_handler is not None:
                         self.ddp_handler.register_comm_hook(model)
+            elif self.distributed_type == DistributedType.TP:
+                model.tensor_parallel(self.state.torch_tp_plugin.torch_device_mesh["tp"])
             elif self.distributed_type == DistributedType.FSDP:
                 # We need to fix the optimizer *before* sharding the model
                 from torch.distributed.fsdp.fully_sharded_data_parallel import FullyShardedDataParallel as FSDP
@@ -2117,6 +2125,7 @@ def prepare_data_loader(
             data_seed=self.dataloader_config.data_seed,
             non_blocking=self.non_blocking,
             use_stateful_dataloader=self.use_stateful_dataloader,
+            torch_device_mesh=self.state.torch_tp_plugin.torch_device_mesh if self.state.torch_tp_plugin else None,
         )
         self._dataloaders.append(prepared_data_loader)
         return prepared_data_loader

src/accelerate/data_loader.py

@@ -713,6 +713,7 @@ def __init__(
         _drop_last: bool = False,
         _non_blocking: bool = False,
         slice_fn=None,
+        torch_device_mesh=None,
         **kwargs,
     ):
         shuffle = False
@@ -732,15 +733,37 @@ def __init__(
         self._drop_last = _drop_last
         self._non_blocking = _non_blocking
         self.skip_batches = skip_batches
+        self.torch_device_mesh = torch_device_mesh
 
         self.slice_fn = slice_tensors if slice_fn is None else slice_fn
         self.iteration = 0
 
+        # if a device mesh is provided extract each dimension (tp and dp)
+        # device mesh will be used only if there is tp involved
+        # otherwise the default behavour should be sufficient
+        self.submesh_tp = None
+        self.submesh_dp = None
+        if self.torch_device_mesh and "tp" in self.torch_device_mesh.mesh_dim_names:
+            # extract torch sub device mesh objects
+            self.submesh_tp = self.torch_device_mesh["tp"]
+            if "dp" in self.torch_device_mesh.mesh_dim_names:
+                self.submesh_dp = self.torch_device_mesh["dp"]
+        if self.submesh_tp and self.submesh_dp:
+            raise ValueError("TP + DDP / TP + FSDP is not yet supported")
+
     def _fetch_batches(self, iterator):
         batches, batch = None, None
         # On process 0, we gather the batch to dispatch.
         if self.state.process_index == 0:
+            # Procedure to support TP only is simpler
+            # since we want to dispatch the same batch of samples across all ranks
+            # this removes complexity of handling multiple tp rank groups when TP + DP
+            # combination is involved.
+
             try:
+                # for TP case avoid using split_batches
+                # since it would mean that the dataloader should be spilling out
+                # duplicates of batches.
                 if self.split_batches:
                     # One batch of the main iterator is dispatched and split.
                     self._update_state_dict()
@@ -749,9 +772,15 @@ def _fetch_batches(self, iterator):
                     # num_processes batches of the main iterator are concatenated then dispatched and split.
                     # We add the batches one by one so we have the remainder available when drop_last=False.
                     batches = []
-                    for _ in range(self.state.num_processes):
+                    if self.submesh_tp:
+                        # when tp, extract single batch and then replicate
                         self._update_state_dict()
-                        batches.append(next(iterator))
+                        batch = next(iterator)
+                        batches = [batch] * self.state.num_processes
+                    else:
+                        for _ in range(self.state.num_processes):
+                            self._update_state_dict()
+                            batches.append(next(iterator))
                     try:
                         batch = concatenate(batches, dim=0)
                     except RuntimeError as e:
@@ -942,6 +971,7 @@ def prepare_data_loader(
     data_seed: Optional[int] = None,
     non_blocking: bool = False,
     use_stateful_dataloader: bool = False,
+    torch_device_mesh: torch.distributed.DeviceMesh = None,
 ) -> DataLoader:
     """
     Wraps a PyTorch `DataLoader` to generate batches for one of the processes only.
@@ -1009,6 +1039,8 @@ def prepare_data_loader(
             "If set to true, the dataloader prepared by the Accelerator will be backed by "
             "[torchdata.StatefulDataLoader](https://github.com/pytorch/data/tree/main/torchdata/stateful_dataloader).
             This requires `torchdata` version 0.8.0 or higher that supports StatefulDataLoader to be installed."
+        torch_device_mesh (`torch.distributed.DeviceMesh`, *optional*, defaults to `None`):
+            PyTorch device mesh.
 
 
     Returns:
@@ -1144,6 +1176,7 @@ def prepare_data_loader(
             _non_blocking=non_blocking,
             slice_fn=slice_fn_for_dispatch,
             use_stateful_dataloader=use_stateful_dataloader,
+            torch_device_mesh=torch_device_mesh,
             **kwargs,
         )
     elif sampler_is_batch_sampler:

src/accelerate/state.py

@@ -850,6 +850,7 @@ def __init__(
         dynamo_plugin=None,
         deepspeed_plugin=None,
         fsdp_plugin=None,
+        torch_tp_plugin=None,
         megatron_lm_plugin=None,
         _from_accelerator: bool = False,
         **kwargs,
@@ -864,6 +865,7 @@ def __init__(
         if not self.initialized:
             self.deepspeed_plugins = None
             self.use_ipex = None
+            self.torch_tp_plugin = torch_tp_plugin
             mixed_precision = (
                 parse_choice_from_env("ACCELERATE_MIXED_PRECISION", "no")
                 if mixed_precision is None
@@ -921,6 +923,8 @@ def __init__(
                     self.distributed_type = DistributedType.MEGATRON_LM
                     megatron_lm_plugin.set_mixed_precision(self._mixed_precision)
                     self.megatron_lm_plugin = megatron_lm_plugin
+                if os.environ.get("ACCELERATE_USE_TP", "false") == "true" or self.torch_tp_plugin is not None:
+                    self.distributed_type = DistributedType.TP
             elif self.distributed_type in [DistributedType.MULTI_CPU, DistributedType.MULTI_XPU, DistributedType.NO]:
                 if is_ipex_available():
                     # check if user disables it explicitly

src/accelerate/utils/__init__.py

@@ -57,6 +57,7 @@
     SageMakerDistributedType,
     TensorInformation,
     TorchDynamoPlugin,
+    TorchTensorParallelPlugin,
     add_model_config_to_megatron_parser,
 )
 from .environment import (

src/accelerate/utils/constants.py

@@ -46,6 +46,7 @@
 ELASTIC_LOG_LINE_PREFIX_TEMPLATE_PYTORCH_VERSION = "2.2.0"
 XPU_PROFILING_AVAILABLE_PYTORCH_VERSION = "2.4.0"
 MITA_PROFILING_AVAILABLE_PYTORCH_VERSION = "2.1.0"
+BETA_TP_AVAILABLE_PYTORCH_VERSION = "2.3.0"
 
 STR_OPERATION_TO_FUNC = {">": op.gt, ">=": op.ge, "==": op.eq, "!=": op.ne, "<=": op.le, "<": op.lt}
 
@@ -76,7 +77,7 @@
     "master_port",
 ]
 
-CUDA_DISTRIBUTED_TYPES = ["DEEPSPEED", "MULTI_GPU", "FSDP", "MEGATRON_LM"]
+CUDA_DISTRIBUTED_TYPES = ["DEEPSPEED", "MULTI_GPU", "FSDP", "MEGATRON_LM", "TP"]
 TORCH_DISTRIBUTED_OPERATION_TYPES = CUDA_DISTRIBUTED_TYPES + [
     "MULTI_NPU",
     "MULTI_MLU",

src/accelerate/utils/dataclasses.py

@@ -30,6 +30,7 @@
 import torch
 
 from .constants import (
+    BETA_TP_AVAILABLE_PYTORCH_VERSION,
     FSDP_AUTO_WRAP_POLICY,
     FSDP_BACKWARD_PREFETCH,
     FSDP_SHARDING_STRATEGY,
@@ -540,6 +541,7 @@ class DistributedType(str, enum.Enum):
     MULTI_XPU = "MULTI_XPU"
     DEEPSPEED = "DEEPSPEED"
     FSDP = "FSDP"
+    TP = "TP"
     XLA = "XLA"
     MEGATRON_LM = "MEGATRON_LM"
 
@@ -1810,6 +1812,32 @@ def set_mixed_precision(self, mixed_precision, buffer_autocast=False, override=F
             self.mixed_precision_policy = MixedPrecision(**self.mixed_precision_policy)
 
 
+@dataclass
+class TorchTensorParallelPlugin:
+    """
+    This plugin is used to enable tensor parallelism using PyTorch >= 2.0.
+    """
+
+    tp_size: int = field(
+        default=1,
+        metadata={"help": "tensor parallel size will be used in the device mesh preparation"},
+    )
+
+    # type has to be "torch.distributed.DeviceMesh"
+    torch_device_mesh: torch.distributed.DeviceMesh = field(default=None)
+
+    def __post_init__(self):
+        if is_torch_version("<", BETA_TP_AVAILABLE_PYTORCH_VERSION):
+            raise ValueError(
+                f"Minimum PyTorch version {BETA_TP_AVAILABLE_PYTORCH_VERSION} needed to use tensor parallel."
+            )
+        from torch.distributed.device_mesh import init_device_mesh
+
+        mesh_dim_name = "tp"
+        device = "cuda"  # support for other devices has to be investigated
+        self.torch_device_mesh = init_device_mesh(device, (self.tp_size,), mesh_dim_names=(mesh_dim_name,))
+
+
 @dataclass
 class MegatronLMPlugin:
     """