[Kernels] Enable FlashInfer FP8 Blockscale on SM90 (for TEP DSR1) (#27134)

Signed-off-by: Duncan Moss <djm.moss@gmail.com>
Co-authored-by: Robert Shaw <114415538+robertgshaw2-redhat@users.noreply.github.com>
Co-authored-by: Wentao Ye <44945378+yewentao256@users.noreply.github.com>

vllm/model_executor/layers/fused_moe/flashinfer_cutlass_moe.py

@@ -57,6 +57,7 @@ class FlashInferExperts(mk.FusedMoEPermuteExpertsUnpermute):
         tp_rank: int = 0,
         tp_size: int = 1,
         use_dp: bool = False,
+        use_deepseek_fp8_block_scale: bool = False,
     ):
         super().__init__(quant_config)
         assert quant_config.quant_dtype in ("nvfp4", torch.float8_e4m3fn, None), (
@@ -69,6 +70,10 @@ class FlashInferExperts(mk.FusedMoEPermuteExpertsUnpermute):
         self.tp_size = tp_size
         self.out_dtype = out_dtype
         self.use_dp = use_dp
+        # Enables DeepSeek-style FP8 block-scale path:
+        # - pass per-block weight scales to the kernel
+        # - skip input activation quantization (kernel applies scaling)
+        self.use_deepseek_fp8_block_scale = use_deepseek_fp8_block_scale
 
     @property
     def activation_formats(
@@ -147,7 +152,12 @@ class FlashInferExperts(mk.FusedMoEPermuteExpertsUnpermute):
             "Only activation silu is supported in FlashInferExperts"
         )
 
-        if self.quant_dtype == torch.float8_e4m3fn:
+        # Select quantization metadata based on FP8 format/path
+        if (
+            self.quant_dtype == torch.float8_e4m3fn
+            and not self.use_deepseek_fp8_block_scale
+        ):
+            # FP8 per-tensor path: use global alphas/scales; do not pass input_sf
             quant_scales = [
                 self.g1_alphas,
                 self.a2_gscale,
@@ -176,6 +186,15 @@ class FlashInferExperts(mk.FusedMoEPermuteExpertsUnpermute):
             # FlashInfer API requires weight to be long for nvfp4
             fc1_expert_weights = w1.view(torch.long)
             fc2_expert_weights = w2.view(torch.long)
+        elif self.use_deepseek_fp8_block_scale:
+            # FP8 block-scale path: provide block-scale weights, omit a1q_scale
+            quant_scales = [
+                self.w1_scale,
+                self.w2_scale,
+            ]
+            a1q_scale = None
+            fc1_expert_weights = w1
+            fc2_expert_weights = w2
         else:
             quant_scales = None
             a1q_scale = None
@@ -196,6 +215,8 @@ class FlashInferExperts(mk.FusedMoEPermuteExpertsUnpermute):
             ep_size=self.ep_size,
             ep_rank=self.ep_rank,
             output=output,
+            # Informs FlashInfer to use the block-scale decoding path when True
+            use_deepseek_fp8_block_scale=self.use_deepseek_fp8_block_scale,
         )
 
 

vllm/model_executor/layers/fused_moe/flashinfer_cutlass_prepare_finalize.py

@@ -28,11 +28,15 @@ class FlashInferCutlassMoEPrepareAndFinalize(mk.FusedMoEPrepareAndFinalize):
         self,
         use_dp: bool,
         num_dispatchers: int = 1,
+        use_deepseek_fp8_block_scale: bool = False,
     ):
         super().__init__()
         self.num_dispatchers_ = num_dispatchers
         self.use_dp = use_dp
         self.local_tokens = None
+        # Toggle for DeepSeek-style FP8 block-scale path where activations are
+        # not quantized here and weight block scales are consumed by the kernel.
+        self.use_deepseek_fp8_block_scale = use_deepseek_fp8_block_scale
 
     @property
     def activation_format(self) -> mk.FusedMoEActivationFormat:
@@ -73,8 +77,9 @@ class FlashInferAllToAllMoEPrepareAndFinalize(FlashInferCutlassMoEPrepareAndFina
         self,
         use_dp: bool,
         num_dispatchers: int = 1,
+        use_deepseek_fp8_block_scale: bool = False,
     ):
-        super().__init__(use_dp, num_dispatchers)
+        super().__init__(use_dp, num_dispatchers, use_deepseek_fp8_block_scale)
         self.alltoall_info = None
 
         # Initialize all2all_manager only for DP case
@@ -97,7 +102,8 @@ class FlashInferAllToAllMoEPrepareAndFinalize(FlashInferCutlassMoEPrepareAndFina
         )
 
         if not self.use_dp:
-            # Non-DP case: standard quantization
+            # Non-DP case: quantize activations unless using block-scale path
+            if not self.use_deepseek_fp8_block_scale:
                 a1q, a1q_scale = moe_kernel_quantize_input(
                     a1,
                     quant_config.a1_gscale,
@@ -106,6 +112,9 @@ class FlashInferAllToAllMoEPrepareAndFinalize(FlashInferCutlassMoEPrepareAndFina
                     quant_config.block_shape,
                     is_fp4_scale_swizzled=not self.use_dp,
                 )
+            else:
+                a1q = a1
+                a1q_scale = None
         else:
             # DP case: use FlashInfer AllToAll
             global_num_tokens_cpu = get_local_sizes()
@@ -122,6 +131,7 @@ class FlashInferAllToAllMoEPrepareAndFinalize(FlashInferCutlassMoEPrepareAndFina
                     top_k,
                     num_experts,
                     quant_config,
+                    use_deepseek_fp8_block_scale=self.use_deepseek_fp8_block_scale,
                 )
             )
 
@@ -154,8 +164,9 @@ class FlashInferAllGatherMoEPrepareAndFinalize(FlashInferCutlassMoEPrepareAndFin
         self,
         use_dp: bool,
         num_dispatchers: int = 1,
+        use_deepseek_fp8_block_scale: bool = False,
     ):
-        super().__init__(use_dp, num_dispatchers)
+        super().__init__(use_dp, num_dispatchers, use_deepseek_fp8_block_scale)
 
     def prepare(
         self,
@@ -173,6 +184,7 @@ class FlashInferAllGatherMoEPrepareAndFinalize(FlashInferCutlassMoEPrepareAndFin
         if not self.use_dp and quant_config.quant_dtype == "nvfp4":
             return a1, None, None, topk_ids, topk_weights
 
+        if not self.use_deepseek_fp8_block_scale:
             a1q, a1q_scale = moe_kernel_quantize_input(
                 a1,
                 quant_config.a1_gscale,
@@ -181,14 +193,33 @@ class FlashInferAllGatherMoEPrepareAndFinalize(FlashInferCutlassMoEPrepareAndFin
                 quant_config.block_shape,
                 is_fp4_scale_swizzled=not self.use_dp,
             )
+        else:
+            # Block-scale path: pass activations through, omit per-token scales
+            a1q = a1
+            a1q_scale = None
 
         if self.use_dp:
-            topk_weights, topk_ids, a1q, a1q_scale = get_dp_group().all_gatherv(
-                [topk_weights, topk_ids, a1q, a1q_scale],
+            # Build gather list conditionally - omit a1q_scale if None
+            # (block-scale path)
+            gather_list = [topk_weights, topk_ids, a1q]
+            if a1q_scale is not None:
+                gather_list.append(a1q_scale)
+                gathered = get_dp_group().all_gatherv(
+                    gather_list,
                     dim=0,
                     sizes=get_local_sizes(),
                 )
-        if quant_config.quant_dtype == "nvfp4":
+                topk_weights, topk_ids, a1q, a1q_scale = gathered
+            else:
+                gathered = get_dp_group().all_gatherv(
+                    gather_list,
+                    dim=0,
+                    sizes=get_local_sizes(),
+                )
+                topk_weights, topk_ids, a1q = gathered
+                a1q_scale = None
+
+        if quant_config.quant_dtype == "nvfp4" and a1q_scale is not None:
             a1q_scale = nvfp4_block_scale_interleave(a1q_scale)
 
         return a1q, a1q_scale, None, topk_ids, topk_weights
@@ -221,6 +252,7 @@ def flashinfer_alltoall_dispatch(
     top_k: int,
     num_experts: int,
     quant_config: FusedMoEQuantConfig,
+    use_deepseek_fp8_block_scale: bool = False,
 ):
     from flashinfer.comm.trtllm_alltoall import MnnvlMoe
 
@@ -250,6 +282,7 @@ def flashinfer_alltoall_dispatch(
     )
     topk_weights = topk_weights.view(dtype=orig_topk_weights_dtype)
 
+    if not use_deepseek_fp8_block_scale:
         x, x_sf = moe_kernel_quantize_input(
             x,
             gs,
@@ -273,7 +306,18 @@ def flashinfer_alltoall_dispatch(
             ep_rank,
             ep_size,
         )
+        if quant_config.quant_dtype == "nvfp4":
             x_sf = nvfp4_block_scale_interleave(x_sf)
+    else:
+        # Block-scale path: pass activations through without quantization
+        x_sf = None
+        x = MnnvlMoe.mnnvl_moe_alltoallv(
+            x,
+            alltoall_info,
+            all2all_manager.workspace_tensor,
+            ep_rank,
+            ep_size,
+        )
     return alltoall_info, topk_ids, topk_weights, x, x_sf
 
 
@@ -304,6 +348,7 @@ def create_flashinfer_prepare_finalize(
     use_dp: bool,
     use_nvfp4: bool = False,
     enable_alltoallv: bool = False,
+    use_deepseek_fp8_block_scale: bool = False,
 ) -> FlashInferCutlassMoEPrepareAndFinalize:
     """Factory function to create the appropriate FlashInfer implementation."""
     if use_nvfp4:
@@ -311,5 +356,7 @@ def create_flashinfer_prepare_finalize(
             return FlashInferAllToAllMoEPrepareAndFinalize(use_dp)
         else:
             return FlashInferAllGatherMoEPrepareAndFinalize(use_dp)
-    # Fp8 only supports AllGather
-    return FlashInferAllGatherMoEPrepareAndFinalize(use_dp)
+    # FP8 path currently supported via AllGather; optionally enable block-scale
+    return FlashInferAllGatherMoEPrepareAndFinalize(
+        use_dp=use_dp, use_deepseek_fp8_block_scale=use_deepseek_fp8_block_scale
+    )

vllm/model_executor/layers/quantization/fp8.py

@@ -3,6 +3,7 @@
 
 from collections.abc import Callable
 from enum import Enum
+from functools import partial
 from typing import TYPE_CHECKING, Any, Optional
 
 import torch
@@ -122,10 +123,13 @@ def get_fp8_moe_backend(block_quant: bool) -> Fp8MoeBackend:
     Select the primary FP8 MoE backend
     Note: Shape-specific fallbacks may still occur at runtime.
     """
-    # prefer FlashInfer backends when available and enabled on supported GPUs
+    # Prefer FlashInfer backends on supported GPUs; allow SM90 and SM100.
     if (
         current_platform.is_cuda()
-        and current_platform.is_device_capability(100)
+        and (
+            current_platform.is_device_capability(100)
+            or current_platform.is_device_capability(90)
+        )
         and envs.VLLM_USE_FLASHINFER_MOE_FP8
         and has_flashinfer_moe()
     ):
@@ -134,14 +138,14 @@ def get_fp8_moe_backend(block_quant: bool) -> Fp8MoeBackend:
             logger.info_once("Using FlashInfer FP8 MoE TRTLLM backend for SM100")
             return Fp8MoeBackend.FLASHINFER_TRTLLM
         else:
-            if block_quant:
+            if block_quant and current_platform.is_device_capability(100):
                 raise ValueError(
                     "FlashInfer FP8 MoE throughput backend does not "
                     "support block quantization. Please use "
                     "VLLM_FLASHINFER_MOE_BACKEND=latency "
                     "instead."
                 )
-            logger.info_once("Using FlashInfer FP8 MoE CUTLASS backend for SM100")
+            logger.info_once("Using FlashInfer FP8 MoE CUTLASS backend for SM90/SM100")
             return Fp8MoeBackend.FLASHINFER_CUTLASS
 
     # weight-only path for older GPUs without native FP8
@@ -641,6 +645,16 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             self.flashinfer_moe_backend = FlashinferMoeBackend.TENSORRT_LLM
         elif self.fp8_backend == Fp8MoeBackend.FLASHINFER_CUTLASS:
             self.flashinfer_moe_backend = FlashinferMoeBackend.CUTLASS
+            if self.block_quant:
+                assert self.weight_block_size == [128, 128], (
+                    f"Only support weight_block_size == [128, 128], "
+                    f"got {self.weight_block_size}"
+                )
+            self.flashinfer_moe_fn = partial(
+                flashinfer_cutlass_moe_fp8,
+                moe=self.moe,
+                use_deepseek_fp8_block_scale=self.block_quant,
+            )
 
         self.allow_deep_gemm = self.fp8_backend == Fp8MoeBackend.DEEPGEMM
         self.allow_cutlass_block_scaled_grouped_gemm = (
@@ -1012,8 +1026,15 @@ class Fp8MoEMethod(FusedMoEMethodBase):
         ):
             return None
         elif self.flashinfer_moe_backend == FlashinferMoeBackend.CUTLASS:
+            if self.block_quant:
+                assert self.weight_block_size == [128, 128], (
+                    f"Only support weight_block_size == [128, 128], "
+                    f"got {self.weight_block_size}"
+                )
+            # Wire block-scale flag through prepare/finalize when using CUTLASS
             prepare_finalize = build_flashinfer_fp8_cutlass_moe_prepare_finalize(
-                self.moe
+                self.moe,
+                use_deepseek_fp8_block_scale=self.block_quant,
             )
             logger.debug_once("%s", prepare_finalize.__class__.__name__)
             return prepare_finalize
@@ -1062,9 +1083,11 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             )
 
         elif self.flashinfer_moe_backend == FlashinferMoeBackend.CUTLASS:
+            # Select GEMM experts with block-scale when weights are block-quantized
             experts = select_cutlass_fp8_gemm_impl(
                 self.moe,
                 self.moe_quant_config,
+                use_deepseek_fp8_block_scale=self.block_quant,
             )
             logger.debug_once("Using %s", experts.__class__.__name__)
             return experts
@@ -1251,16 +1274,17 @@ class Fp8MoEMethod(FusedMoEMethodBase):
                 workspace=layer.workspace,
             )
         elif self.flashinfer_moe_backend == FlashinferMoeBackend.CUTLASS:
-            assert not self.block_quant
-            assert not renormalize and custom_routing_function is not None
             assert activation == "silu", (
                 f"Expected 'silu' activation but got {activation}"
             )
+            if not self.block_quant:
+                assert not renormalize and custom_routing_function is not None
                 assert scoring_func == "sigmoid", (
                     f"Expected 'sigmoid' scoring func but got {scoring_func}"
                 )
-
-            result = flashinfer_cutlass_moe_fp8(
+            # Delegate to CUTLASS FlashInfer path; function already bound with
+            # use_deepseek_fp8_block_scale for block-quant when applicable
+            result = self.flashinfer_moe_fn(
                 x,
                 layer,
                 topk_weights,

vllm/model_executor/layers/quantization/utils/flashinfer_utils.py

@@ -17,6 +17,7 @@ from vllm.model_executor.layers.fused_moe.flashinfer_cutlass_moe import (
 from vllm.model_executor.layers.fused_moe.flashinfer_cutlass_prepare_finalize import (  # noqa: E501
     create_flashinfer_prepare_finalize,
 )
+from vllm.platforms import current_platform
 
 logger = init_logger(__name__)
 
@@ -190,17 +191,22 @@ def register_moe_scaling_factors(layer: torch.nn.Module) -> None:
 
 
 def build_flashinfer_fp8_cutlass_moe_prepare_finalize(
-    moe: FusedMoEConfig | None,
+    moe: FusedMoEConfig | None, use_deepseek_fp8_block_scale: bool = False
 ) -> mk.FusedMoEPrepareAndFinalize:
     """Create a FlashInfer CUTLASS fused-MoE prepare finalize kernel"""
     use_dp = moe.moe_parallel_config.dp_size > 1 if moe is not None else False
-    return create_flashinfer_prepare_finalize(use_dp)
+    # Propagate block-scale flag so prepare/finalize can skip act quantization
+    # and inform the kernel to consume per-block weight scales.
+    return create_flashinfer_prepare_finalize(
+        use_dp, use_deepseek_fp8_block_scale=use_deepseek_fp8_block_scale
+    )
 
 
 def select_cutlass_fp8_gemm_impl(
     moe: FusedMoEConfig | None,
     quant_config: FusedMoEQuantConfig,
     out_dtype: torch.dtype | None = None,
+    use_deepseek_fp8_block_scale: bool = False,
 ) -> mk.FusedMoEPermuteExpertsUnpermute:
     """Return a GEMM *experts* implementation for fused-MoE layers"""
 
@@ -212,12 +218,14 @@ def select_cutlass_fp8_gemm_impl(
             ep_size=moe.moe_parallel_config.ep_size,
             tp_rank=moe.moe_parallel_config.tp_rank,
             tp_size=moe.moe_parallel_config.tp_size,
+            use_deepseek_fp8_block_scale=use_deepseek_fp8_block_scale,
         )
 
     assert out_dtype is not None, "If moe config is None, out_dtype must be passed"
     return FlashInferExperts(
         out_dtype=out_dtype,
         quant_config=quant_config,
+        use_deepseek_fp8_block_scale=use_deepseek_fp8_block_scale,
     )
 
 
@@ -231,14 +239,22 @@ def flashinfer_cutlass_moe_fp8(
     global_num_experts: int = -1,
     expert_map: torch.Tensor | None = None,
     apply_router_weight_on_input: bool = False,
+    use_deepseek_fp8_block_scale: bool = False,
+    moe: FusedMoEConfig | None = None,
 ) -> torch.Tensor:
     quant_config = layer.quant_method.get_fused_moe_quant_config(layer)
     assert quant_config is not None
 
+    # Construct modular kernel with block-scale support when requested.
     fused_experts = mk.FusedMoEModularKernel(
-        build_flashinfer_fp8_cutlass_moe_prepare_finalize(moe=None),
+        build_flashinfer_fp8_cutlass_moe_prepare_finalize(
+            moe=moe, use_deepseek_fp8_block_scale=use_deepseek_fp8_block_scale
+        ),
         select_cutlass_fp8_gemm_impl(
-            moe=None, quant_config=quant_config, out_dtype=hidden_states.dtype
+            moe=moe,
+            quant_config=quant_config,
+            out_dtype=hidden_states.dtype,
+            use_deepseek_fp8_block_scale=use_deepseek_fp8_block_scale,
         ),
     )
 
@@ -258,7 +274,10 @@ def flashinfer_cutlass_moe_fp8(
 
 def get_flashinfer_moe_backend() -> FlashinferMoeBackend:
     flashinfer_moe_backend = envs.VLLM_FLASHINFER_MOE_BACKEND
-    if flashinfer_moe_backend == "throughput":
+    # Prefer CUTLASS on SM90 to cover both SM90/SM100 generations
+    if flashinfer_moe_backend == "throughput" or current_platform.is_device_capability(
+        90
+    ):
         return FlashinferMoeBackend.CUTLASS
     elif flashinfer_moe_backend == "latency":
         return FlashinferMoeBackend.TENSORRT_LLM