Make torch TP composable with torchao

Customize parallel style to perform local sharding instead of scatter

worked configs:
TP + int8wo, TP + fp8wo

python/sglang/srt/model_parallel.py

@@ -2,25 +2,69 @@
 Common utilities for torch model parallelism.
 """
 
-from typing import Optional
+from typing import Optional, Sequence
 
 import torch
+import torch.nn as nn
 from torch.distributed.device_mesh import DeviceMesh
 
 try:
-    from torch.distributed.tensor import DTensor, Shard
+    import torch.distributed.tensor as dt
 except ImportError:
     # torch 2.4 or older
-    from torch.distributed._tensor import DTensor, Shard
+    import torch.distributed._tensor as dt
 
-from torch.distributed._functional_collectives import AsyncCollectiveTensor
 from torch.distributed.tensor.parallel import (
     ColwiseParallel,
     RowwiseParallel,
     parallelize_module,
 )
 
 
+def _shard_tensor(
+    full_tensor: torch.Tensor,
+    device_mesh: DeviceMesh,
+    placements: Sequence[dt.Shard],
+) -> "dt.DTensor":
+    """
+    Locally shards a full tensor based on indicated sharding arrangement, and
+    returns a DTensor containing the local shard.
+
+    .. warning:: This is a private API that is subject to change. It skips the
+        communication otherwise required by `distribute_tensor`. It is only
+        applicable to cases where all ranks have the same `full_tensor`. For
+        example, in distributed inference all ranks load from the same
+        checkpoint. This API will not check for data equality between ranks, it
+        is thus user's responsibility to ensure the `full_tensor` is the same
+        across ranks.
+
+    Args:
+        full_tensor (torch.Tensor): the full tensor to be sharded.
+        device_mesh (:class:`DeviceMesh`): DeviceMesh to place the
+            DTensor.  Must have same dimension as the number of placements.
+        placements (Sequence[:class:`Shard`]): the placements that
+            describes how to place the local tensor on DeviceMesh.
+
+    Returns:
+        A :class:`DTensor` object with the shard as its local tensor.
+
+    Examples:
+        >>> # xdoctest: +SKIP("need world_size and rank")
+        >>> device_mesh = dist.init_device_mesh("cuda", (world_size,))
+        >>> full_tensor = torch.arange(world_size, device=f"cuda:{rank}")
+        >>> dtensor = _shard_tensor(full_tensor, device_mesh, [Shard(1)])
+    """
+    shape, offset = dt._utils.compute_local_shape_and_global_offset(
+        full_tensor.shape, device_mesh, placements
+    )
+    slices = [
+        slice(cur_offset, cur_offset + cur_shape)
+        for cur_shape, cur_offset in zip(shape, offset)
+    ]
+    local_tensor = full_tensor[slices]
+    return dt.DTensor.from_local(local_tensor, device_mesh, placements)
+
+
 class ColwiseParallelSharded(ColwiseParallel):
     """
     A version of ColwiseParallel where the local weight has been already
@@ -34,7 +78,7 @@ def _partition_linear_fn(self, name, module, device_mesh):
         # means Colwise as Linear is input * weight^T + bias, where
         # weight would become Shard(1)
         for name, param in module.named_parameters():
-            dtensor = DTensor.from_local(param, device_mesh, [Shard(0)])
+            dtensor = dt.DTensor.from_local(param, device_mesh, [dt.Shard(0)])
             dist_param = torch.nn.Parameter(dtensor, requires_grad=False)
             module.register_parameter(name, dist_param)
 
@@ -47,6 +91,23 @@ class RowwiseParallelMaybeWait(RowwiseParallel):
     AsyncCollectiveTensor and custom ops, such as `class RMSNorm(CustomOp)`.
     """
 
+    def _partition_linear_fn(self, name, module, device_mesh):
+        # Rowwise shard weight to Shard(1), bias to Replicate(), weight be Shard(1)
+        # means Rowwise as nn.Linear is input * weight^T + bias, where
+        # weight would become Shard(0)
+        module.register_parameter(
+            "weight",
+            nn.Parameter(_shard_tensor(module.weight, device_mesh, [dt.Shard(1)])),
+        )
+        if getattr(module, "bias", None) is not None:
+            # The Linear module has bias
+            module.register_parameter(
+                "bias",
+                nn.Parameter(
+                    dt.distribute_tensor(module.bias, device_mesh, [dt.Replicate()])
+                ),
+            )
+
     @staticmethod
     def _prepare_output_fn(output_layouts, use_local_output, mod, outputs, device_mesh):
         outputs = super(