[Feat][Perf] Enable deepep-low-latency with round-robin expert placement. (#28449)

Signed-off-by: bruceszchen <bruceszchen@tencent.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/model_executor/layers/fused_moe/all2all_utils.py

@@ -67,6 +67,7 @@ def maybe_roundup_layer_hidden_size(
 def maybe_make_prepare_finalize(
     moe: FusedMoEConfig,
     quant_config: FusedMoEQuantConfig | None,
+    routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
 ) -> FusedMoEPrepareAndFinalize | None:
     if not moe.moe_parallel_config.use_all2all_kernels:
         return None
@@ -134,6 +135,13 @@ def maybe_make_prepare_finalize(
 
     elif moe.use_deepep_ll_kernels:
         assert quant_config is not None
+        global_to_physical = physical_to_global = local_expert_global_ids = None
+        if routing_tables is not None:
+            (
+                global_to_physical,
+                physical_to_global,
+                local_expert_global_ids,
+            ) = routing_tables
         all_to_all_args = dict(
             max_num_tokens_per_dp_rank=moe.max_num_tokens,
             token_hidden_size=moe.hidden_dim,
@@ -155,6 +163,9 @@ def maybe_make_prepare_finalize(
             max_tokens_per_rank=moe.max_num_tokens,
             num_dispatchers=all2all_manager.world_size,
             use_fp8_dispatch=use_fp8_dispatch,
+            global_to_physical=global_to_physical,
+            physical_to_global=physical_to_global,
+            local_expert_global_ids=local_expert_global_ids,
         )
 
     return prepare_finalize

vllm/model_executor/layers/fused_moe/deepep_ll_prepare_finalize.py

@@ -85,6 +85,9 @@ class DeepEPLLPrepareAndFinalize(mk.FusedMoEPrepareAndFinalize):
         max_tokens_per_rank: int,
         num_dispatchers: int,
         use_fp8_dispatch: bool = False,
+        global_to_physical: torch.Tensor | None = None,
+        physical_to_global: torch.Tensor | None = None,
+        local_expert_global_ids: torch.Tensor | None = None,
     ):
         super().__init__()
 
@@ -97,6 +100,17 @@ class DeepEPLLPrepareAndFinalize(mk.FusedMoEPrepareAndFinalize):
         self.handles: list[tuple | None] = [None, None]
         self.num_dispatchers_ = num_dispatchers
 
+        topk_indices_dtype = self.topk_indices_dtype()
+
+        def _maybe_cast(tensor: torch.Tensor | None) -> torch.Tensor | None:
+            if tensor is None or topk_indices_dtype is None:
+                return tensor
+            return tensor.to(dtype=topk_indices_dtype)
+
+        self.global_to_physical = _maybe_cast(global_to_physical)
+        self.physical_to_global = _maybe_cast(physical_to_global)
+        self.local_expert_global_ids = _maybe_cast(local_expert_global_ids)
+
         # We don't have enough information to determine if we should dispatch
         # activation scales in a packed ue8m0 format during object construction
         # time. This setting is handled by post_init_setup.
@@ -136,6 +150,16 @@ class DeepEPLLPrepareAndFinalize(mk.FusedMoEPrepareAndFinalize):
     def topk_indices_dtype(self) -> torch.dtype | None:
         return torch.int64
 
+    def _map_global_to_physical_ids(self, topk_ids: torch.Tensor) -> torch.Tensor:
+        if self.global_to_physical is None:
+            return topk_ids
+        return self.global_to_physical[topk_ids]
+
+    def _map_local_to_global_ids(self, expert_topk_ids: torch.Tensor) -> torch.Tensor:
+        if self.local_expert_global_ids is None:
+            return expert_topk_ids
+        return self.local_expert_global_ids[expert_topk_ids]
+
     def _do_quant(
         self,
         x: torch.Tensor | tuple[torch.Tensor, torch.Tensor],
@@ -226,9 +250,10 @@ class DeepEPLLPrepareAndFinalize(mk.FusedMoEPrepareAndFinalize):
             a1 = a1 * topk_weights.to(a1.dtype)
 
         # Dispatch
+        dispatch_topk_ids = self._map_global_to_physical_ids(topk_ids)
         expert_x, expert_num_tokens, handle, _, hook = self.buffer.low_latency_dispatch(
             a1,
-            topk_ids,
+            dispatch_topk_ids,
             self.max_tokens_per_rank,
             num_experts,
             use_fp8=self.use_fp8_dispatch,
@@ -313,11 +338,12 @@ class DeepEPLLPrepareAndFinalize(mk.FusedMoEPrepareAndFinalize):
             # weights have already been applied.
             combine_topk_weights = torch.ones_like(topk_weights)
 
+        combine_topk_ids = self._map_global_to_physical_ids(topk_ids)
         # TODO (varun) : Enable zero copy mode
         dbo_maybe_run_recv_hook()
         _, _, recv_hook = self.buffer.low_latency_combine(
             fused_expert_output,
-            topk_ids,
+            combine_topk_ids,
             combine_topk_weights,
             handle,
             async_finish=False,

vllm/model_executor/layers/fused_moe/fused_moe_method_base.py

@@ -50,10 +50,15 @@ class FusedMoEMethodBase(QuantizeMethodBase):
         """
         return False
 
-    def maybe_make_prepare_finalize(self) -> FusedMoEPrepareAndFinalize | None:
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> FusedMoEPrepareAndFinalize | None:
         from .all2all_utils import maybe_make_prepare_finalize
 
-        return maybe_make_prepare_finalize(self.moe, self.moe_quant_config)
+        return maybe_make_prepare_finalize(
+            self.moe, self.moe_quant_config, routing_tables
+        )
 
     def select_gemm_impl(
         self,

vllm/model_executor/layers/fused_moe/layer.py

@@ -5,7 +5,7 @@ from collections.abc import Callable, Iterable
 from contextlib import nullcontext
 from enum import Enum
 from functools import partial
-from typing import Literal, get_args, overload
+from typing import Literal, cast, get_args, overload
 
 import torch
 import torch.nn.functional as F
@@ -192,6 +192,42 @@ def determine_expert_map(
     return (local_num_experts, expert_map, expert_mask)
 
 
+def determine_expert_placement_strategy(
+    expert_placement_strategy: ExpertPlacementStrategy,
+    moe_parallel_config: FusedMoEParallelConfig,
+    num_expert_group: int | None,
+    num_redundant_experts: int,
+    enable_eplb: bool,
+) -> ExpertPlacementStrategy:
+    if expert_placement_strategy == "round_robin":
+        round_robin_supported = (
+            (num_expert_group is not None and num_expert_group > 1)
+            and num_redundant_experts == 0
+            and not enable_eplb
+        )
+
+        if not round_robin_supported:
+            logger.warning(
+                "Round-robin expert placement is only supported for "
+                "models with multiple expert groups and no redundant "
+                "experts. Falling back to linear expert placement."
+            )
+            return "linear"
+        if (
+            moe_parallel_config.use_all2all_kernels
+            and not moe_parallel_config.use_deepep_ll_kernels
+        ):
+            logger.warning(
+                "Round-robin expert placement currently only supports "
+                "the DeepEP low-latency backend, but '%s' was configured. "
+                "Falling back to linear expert placement.",
+                moe_parallel_config.all2all_backend,
+            )
+            return "linear"
+
+    return expert_placement_strategy
+
+
 def get_compressed_expert_map(expert_map: torch.Tensor) -> str:
     """
     Compresses the expert map by removing any -1 entries.
@@ -400,6 +436,9 @@ class FusedMoE(CustomOp):
         self.expert_load_view: torch.Tensor | None = None
         self.logical_to_physical_map: torch.Tensor | None = None
         self.logical_replica_count: torch.Tensor | None = None
+        self.expert_placement_strategy: ExpertPlacementStrategy = (
+            vllm_config.parallel_config.expert_placement_strategy
+        )
 
         # ROCm aiter shared experts fusion
         self.rocm_aiter_fmoe_enabled = rocm_aiter_ops.is_fused_moe_enabled()
@@ -433,38 +472,27 @@ class FusedMoE(CustomOp):
                     "Redundant experts are only supported with EPLB."
                 )
 
-            expert_placement_strategy = (
-                vllm_config.parallel_config.expert_placement_strategy
-            )
-            if expert_placement_strategy == "round_robin":
-                # TODO(Bruce): will support round robin expert placement with
-                # EPLB enabled in the future.
-                round_robin_supported = (
-                    (num_expert_group is not None and num_expert_group > 1)
-                    and num_redundant_experts == 0
-                    and not self.enable_eplb
-                )
-
-                if not round_robin_supported:
-                    logger.warning(
-                        "Round-robin expert placement is only supported for "
-                        "models with multiple expert groups and no redundant "
-                        "experts. Falling back to linear expert placement."
+            self.expert_placement_strategy = determine_expert_placement_strategy(
+                expert_placement_strategy=self.expert_placement_strategy,
+                moe_parallel_config=self.moe_parallel_config,
+                num_expert_group=num_expert_group,
+                num_redundant_experts=num_redundant_experts,
+                enable_eplb=self.enable_eplb,
             )
-                    expert_placement_strategy = "linear"
 
             self.expert_map: torch.Tensor | None
             local_num_experts, expert_map, expert_mask = determine_expert_map(
                 ep_size=self.ep_size,
                 ep_rank=self.ep_rank,
                 global_num_experts=self.global_num_experts,
-                expert_placement_strategy=expert_placement_strategy,
+                expert_placement_strategy=self.expert_placement_strategy,
                 num_fused_shared_experts=self.num_fused_shared_experts,
                 return_expert_mask=self.rocm_aiter_fmoe_enabled,
             )
             self.local_num_experts = local_num_experts
             self.register_buffer("expert_map", expert_map)
             self.register_buffer("expert_mask", expert_mask)
+            self._maybe_init_expert_routing_tables()
             logger.info_once(
                 "[EP Rank %s/%s] Expert parallelism is enabled. Expert "
                 "placement strategy: %s. Local/global"
@@ -472,7 +500,7 @@ class FusedMoE(CustomOp):
                 " %s.",
                 self.ep_rank,
                 self.ep_size,
-                expert_placement_strategy,
+                self.expert_placement_strategy,
                 self.local_num_experts,
                 self.global_num_experts,
                 get_compressed_expert_map(self.expert_map),
@@ -621,7 +649,12 @@ class FusedMoE(CustomOp):
     # should be safe to swap out the quant_method.
     def maybe_init_modular_kernel(self) -> None:
         self.ensure_moe_quant_config_init()
-        prepare_finalize = self.quant_method.maybe_make_prepare_finalize()
+        # routing_tables only needed for round-robin expert placement with
+        # DeepEP all2all backend.
+        routing_tables = self._maybe_init_expert_routing_tables()
+        prepare_finalize = self.quant_method.maybe_make_prepare_finalize(
+            routing_tables=routing_tables
+        )
         if prepare_finalize is not None:
             logger.debug(
                 "%s for %s(%s)", prepare_finalize.__class__.__name__, self, id(self)
@@ -703,6 +736,84 @@ class FusedMoE(CustomOp):
         # By default, router/gate is called before FusedMoE forward pass
         return False
 
+    def _maybe_init_expert_routing_tables(
+        self,
+    ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None:
+        # Currently routing_tables only needed for round-robin expert placement
+        # with DeepEP-ll all2all backend.
+        if (
+            self.expert_placement_strategy != "round_robin"
+            or not self.use_deepep_ll_kernels
+        ):
+            return None
+
+        if hasattr(self, "expert_global_to_physical"):
+            return cast(
+                tuple[torch.Tensor, torch.Tensor, torch.Tensor],
+                (
+                    self.expert_global_to_physical,
+                    self.expert_physical_to_global,
+                    self.expert_local_to_global,
+                ),
+            )
+
+        if self.expert_map is None:
+            return None
+
+        routing_tables = self.ensure_round_robin_expert_routing_tables(
+            global_num_experts=self.global_num_experts,
+            ep_size=self.ep_size,
+            ep_rank=self.ep_rank,
+            local_num_experts=self.local_num_experts,
+            device=self.expert_map.device,
+        )
+
+        global_to_physical, physical_to_global, local_global = routing_tables
+        self.register_buffer("expert_global_to_physical", global_to_physical)
+        self.register_buffer("expert_physical_to_global", physical_to_global)
+        self.register_buffer("expert_local_to_global", local_global)
+
+        return routing_tables
+
+    @staticmethod
+    def ensure_round_robin_expert_routing_tables(
+        global_num_experts: int,
+        ep_size: int,
+        ep_rank: int,
+        local_num_experts: int,
+        device: torch.device | None = None,
+    ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
+        device_kwargs = {"device": device} if device is not None else {}
+        global_indices = torch.arange(
+            global_num_experts, dtype=torch.long, **device_kwargs
+        )
+        owner = torch.remainder(global_indices, ep_size)
+        local_index = torch.div(global_indices, ep_size, rounding_mode="floor")
+        base = global_num_experts // ep_size
+        remainder = global_num_experts % ep_size
+        physical_offset = owner * base
+        if remainder > 0:
+            remainder_tensor = torch.tensor(
+                remainder, dtype=torch.long, **device_kwargs
+            )
+            physical_offset = physical_offset + torch.minimum(owner, remainder_tensor)
+
+        global_to_physical = physical_offset + local_index
+        physical_to_global = torch.empty_like(global_to_physical)
+        physical_to_global[global_to_physical] = global_indices
+
+        local_global = torch.arange(
+            ep_rank,
+            global_num_experts,
+            ep_size,
+            dtype=torch.long,
+            **device_kwargs,
+        )
+        if local_global.numel() != local_num_experts:
+            local_global = local_global[:local_num_experts]
+
+        return (global_to_physical, physical_to_global, local_global)
+
     def update_expert_map(self):
         # ep_size and ep_rank should already be updated
         assert self.expert_map is not None
@@ -711,12 +822,14 @@ class FusedMoE(CustomOp):
                 ep_size=self.ep_size,
                 ep_rank=self.ep_rank,
                 global_num_experts=self.global_num_experts,
+                expert_placement_strategy=self.expert_placement_strategy,
                 num_fused_shared_experts=self.num_fused_shared_experts,
                 return_expert_mask=self.rocm_aiter_fmoe_enabled,
             )
             self.local_num_experts = local_num_experts
             self.register_buffer("expert_map", expert_map)
             self.register_buffer("expert_mask", expert_mask)
+            self._maybe_init_expert_routing_tables()
             if self.aiter_fmoe_shared_expert_enabled:
                 self._init_aiter_shared_experts_topK_buffer(
                     vllm_config=get_current_vllm_config(),

vllm/model_executor/layers/fused_moe/unquantized_fused_moe_method.py

@@ -108,11 +108,14 @@ class UnquantizedFusedMoEMethod(FusedMoEMethodBase, CustomOp):
     def allow_inplace(self) -> bool:
         return True
 
-    def maybe_make_prepare_finalize(self) -> FusedMoEPrepareAndFinalize | None:
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> FusedMoEPrepareAndFinalize | None:
         if self.rocm_aiter_moe_enabled:
             return None
         else:
-            return super().maybe_make_prepare_finalize()
+            return super().maybe_make_prepare_finalize(routing_tables)
 
     def select_gemm_impl(
         self,

vllm/model_executor/layers/quantization/compressed_tensors/compressed_tensors_moe.py

@@ -380,11 +380,14 @@ class CompressedTensorsW4A4MoeMethod(CompressedTensorsMoEMethod):
             (layer.w2_input_global_scale), requires_grad=False
         )
 
-    def maybe_make_prepare_finalize(self) -> mk.FusedMoEPrepareAndFinalize | None:
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> mk.FusedMoEPrepareAndFinalize | None:
         if self.use_marlin:
             return None
         elif not self.allow_flashinfer:
-            return super().maybe_make_prepare_finalize()
+            return super().maybe_make_prepare_finalize(routing_tables)
 
         prepare_finalize = build_flashinfer_fp4_cutlass_moe_prepare_finalize(self.moe)
         logger.debug_once("%s", prepare_finalize.__class__.__name__)
@@ -890,11 +893,14 @@ class CompressedTensorsW8A8Fp8MoEMethod(CompressedTensorsMoEMethod):
                     layer.w2_weight_scale
                 )
 
-    def maybe_make_prepare_finalize(self) -> mk.FusedMoEPrepareAndFinalize | None:
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> mk.FusedMoEPrepareAndFinalize | None:
         if self.use_marlin or self.rocm_aiter_moe_enabled:
             return None
         else:
-            return super().maybe_make_prepare_finalize()
+            return super().maybe_make_prepare_finalize(routing_tables)
 
     def select_gemm_impl(
         self,

vllm/model_executor/layers/quantization/fp8.py

@@ -1018,7 +1018,10 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             del layer.w13_input_scale
             del layer.w2_input_scale
 
-    def maybe_make_prepare_finalize(self) -> mk.FusedMoEPrepareAndFinalize | None:
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> mk.FusedMoEPrepareAndFinalize | None:
         if (
             self.rocm_aiter_moe_enabled
             or self.use_marlin
@@ -1039,7 +1042,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             logger.debug_once("%s", prepare_finalize.__class__.__name__)
             return prepare_finalize
         else:
-            return super().maybe_make_prepare_finalize()
+            return super().maybe_make_prepare_finalize(routing_tables)
 
     def select_gemm_impl(
         self,

vllm/model_executor/layers/quantization/modelopt.py

@@ -373,6 +373,7 @@ class ModelOptFp8MoEMethod(FusedMoEMethodBase):
 
     def maybe_make_prepare_finalize(
         self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
     ) -> mk.FusedMoEPrepareAndFinalize | None:
         # TRT LLM not supported with all2all yet.
         if self.flashinfer_moe_backend == FlashinferMoeBackend.TENSORRT_LLM:
@@ -384,7 +385,7 @@ class ModelOptFp8MoEMethod(FusedMoEMethodBase):
             logger.debug_once("%s", prepare_finalize.__class__.__name__)
             return prepare_finalize
         else:
-            return super().maybe_make_prepare_finalize()
+            return super().maybe_make_prepare_finalize(routing_tables)
 
     def select_gemm_impl(
         self,
@@ -1179,7 +1180,10 @@ class ModelOptNvFp4FusedMoE(FusedMoEMethodBase):
                 " for ModelOptNvFp4FusedMoE."
             )
 
-    def maybe_make_prepare_finalize(self) -> mk.FusedMoEPrepareAndFinalize | None:
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> mk.FusedMoEPrepareAndFinalize | None:
         if self.use_marlin or (
             self.allow_flashinfer
             and self.flashinfer_moe_backend == FlashinferMoeBackend.TENSORRT_LLM
@@ -1196,7 +1200,7 @@ class ModelOptNvFp4FusedMoE(FusedMoEMethodBase):
             logger.debug_once("%s", prepare_finalize.__class__.__name__)
             return prepare_finalize
         else:
-            return super().maybe_make_prepare_finalize()
+            return super().maybe_make_prepare_finalize(routing_tables)
 
     def select_gemm_impl(
         self,