Support (1 <= dp < tp) in the dp attention in DeepEP (#4770)

Co-authored-by: Cheng Wan <cwan39@gatech.edu>

python/sglang/srt/distributed/parallel_state.py

@@ -439,6 +439,15 @@ class GroupCoordinator:
         else:
             torch.distributed.all_reduce(input_, group=self.device_group)
 
+    def reduce_scatter(
+        self,
+        output: torch.Tensor,
+        input_list: List[torch.Tensor],
+    ) -> None:
+        # TODO(ch-wan): support other backends
+        torch.distributed.reduce_scatter(output, input_list, group=self.device_group)
+        return output
+
     def _all_gather_into_tensor(self, output: torch.Tensor, input: torch.Tensor):
         pynccl_comm = self.pynccl_comm
         if pynccl_comm is not None and not pynccl_comm.disabled:
@@ -456,11 +465,23 @@ class GroupCoordinator:
                 output, input, group_name=self.unique_name
             )
 
-    def all_gather(self, input_: torch.Tensor, dim: int = -1) -> torch.Tensor:
+    def all_gather(
+        self,
+        input_: torch.Tensor,
+        dim: int = -1,
+        tensor_list: List[torch.Tensor] = None,
+    ) -> torch.Tensor:
         world_size = self.world_size
         # Bypass the function if we are using only 1 GPU.
         if world_size == 1:
             return input_
+
+        if tensor_list is not None:
+            # TODO(ch-wan): support other backends
+            return torch.distributed.all_gather(
+                tensor_list, input_, group=self.device_group
+            )
+
         assert (
             -input_.dim() <= dim < input_.dim()
         ), f"Invalid dim ({dim}) for input tensor with shape {input_.size()}"