[Feature] Enable TP + EP `shared_experts` overlap with router, 3.7% E2E...

[Feature] Enable TP + EP `shared_experts` overlap with router, 3.7% E2E performance improvement (#28164)
Signed-off-by: yewentao256 <zhyanwentao@126.com>

vllm/model_executor/layers/fused_moe/layer.py

@@ -1178,7 +1178,7 @@ class FusedMoE(CustomOp):
         hidden_size: Input hidden state size of the transformer
         intermediate_size: Intermediate size of the experts
         params_dtype: Data type for the parameters.
-        reduce_results: Whether to all all_reduce on the output of the layer
+        reduce_results: Whether to all_reduce on the output of the layer
         renormalize: Whether to renormalize the logits in the fused_moe kernel
         quant_config: Quantization configure.
         enable_eplb: Whether to enable expert parallelism load balancer.

vllm/model_executor/layers/fused_moe/shared_fused_moe.py

@@ -3,7 +3,10 @@
 
 import torch
 
-from vllm.distributed import tensor_model_parallel_all_reduce
+from vllm.distributed import (
+    get_tensor_model_parallel_world_size,
+    tensor_model_parallel_all_reduce,
+)
 from vllm.model_executor.layers.fused_moe.layer import FusedMoE
 
 
@@ -25,16 +28,13 @@ class SharedFusedMoE(FusedMoE):
         super().__init__(**kwargs)
         self._shared_experts = shared_experts
 
-        # Disable shared expert overlap if EP is disabled or we are not using
+        # Disable shared expert overlap if we are not using
         # flashinfer + DP since there is nothing to be gained in this case.
         # Disabling the overlap optimization also prevents the shared experts
         # from being hidden from torch.compile.
         self.use_overlapped = (
             use_overlapped
-            and not (
-                self.use_ep
-                or (self.use_flashinfer_cutlass_kernels and self.dp_size > 1)
-            )
+            and not (self.use_flashinfer_cutlass_kernels and self.dp_size > 1)
             and self._shared_experts is not None
         )
 
@@ -65,7 +65,7 @@ class SharedFusedMoE(FusedMoE):
                 # should have been created with reduce_results=False.
                 if (
                     self.reduce_results
-                    and self.tp_size > 1
+                    and get_tensor_model_parallel_world_size() > 1
                     and self.must_reduce_shared_expert_outputs()
                 ):
                     shared_out = tensor_model_parallel_all_reduce(shared_out)
@@ -81,4 +81,12 @@ class SharedFusedMoE(FusedMoE):
                 hidden_states=hidden_states,
                 router_logits=router_logits,
             )
+            # ensure early TP reduction of shared expert outputs when required
+            if (
+                shared_out is not None
+                and self.reduce_results
+                and get_tensor_model_parallel_world_size() > 1
+                and self.must_reduce_shared_expert_outputs()
+            ):
+                shared_out = tensor_model_parallel_all_reduce(shared_out)
         return shared_out, fused_out