[Perf] Add swap_ab to SM90 FP8 non-block CUTLASS moe grouped gemm (#20911)

shixianc · Shixian Cui · web-flow · commit 5780121c95bc · 2025-07-18T04:34:43.000Z
Signed-off-by: Shixian Cui &lt;shixian@amazon.com&gt;
Co-authored-by: Shixian Cui &lt;shixian@amazon.com&gt;
diff --git a/csrc/quantization/cutlass_w8a8/moe/grouped_mm_c3x.cu b/csrc/quantization/cutlass_w8a8/moe/grouped_mm_c3x.cu
@@ -29,19 +29,36 @@ struct sm90_fp8_config_default {
 
 template <typename InType, typename OutType,
           template <typename, typename, typename> typename Epilogue>
-struct sm90_fp8_config_M16 {
-  // M in [1, 16]
+struct sm90_fp8_config_M4 {
+  // M in [1, 4]
   static_assert(std::is_same<InType, cutlass::float_e4m3_t>());
   using KernelSchedule =
       cutlass::gemm::KernelPtrArrayTmaWarpSpecializedPingpongFP8FastAccum;
   using EpilogueSchedule =
       cutlass::epilogue::PtrArrayTmaWarpSpecializedPingpong;
-  using TileShape = cute::Shape<cute::_64, cute::_64, cute::_128>;
-  using ClusterShape = cute::Shape<cute::_1, cute::_4, cute::_1>;
+  using TileShape = cute::Shape<cute::_128, cute::_16, cute::_128>;
+  using ClusterShape = cute::Shape<cute::_1, cute::_1, cute::_1>;
 
   using Cutlass3xGemm =
       cutlass_3x_group_gemm<InType, OutType, Epilogue, TileShape, ClusterShape,
-                            KernelSchedule, EpilogueSchedule>;
+                            KernelSchedule, EpilogueSchedule, true>;
+};
+
+template <typename InType, typename OutType,
+          template <typename, typename, typename> typename Epilogue>
+struct sm90_fp8_config_M64 {
+  // M in (4, 64]
+  static_assert(std::is_same<InType, cutlass::float_e4m3_t>());
+  using KernelSchedule =
+      cutlass::gemm::KernelPtrArrayTmaWarpSpecializedPingpongFP8FastAccum;
+  using EpilogueSchedule =
+      cutlass::epilogue::PtrArrayTmaWarpSpecializedPingpong;
+  using TileShape = cute::Shape<cute::_128, cute::_16, cute::_256>;
+  using ClusterShape = cute::Shape<cute::_2, cute::_1, cute::_1>;
+
+  using Cutlass3xGemm =
+      cutlass_3x_group_gemm<InType, OutType, Epilogue, TileShape, ClusterShape,
+                            KernelSchedule, EpilogueSchedule, true>;
 };
 
 template <typename InType, typename OutType,
@@ -102,7 +119,9 @@ void run_cutlass_moe_mm_sm90(
       InType, OutType, vllm::c3x::ScaledEpilogueArray>::Cutlass3xGemm;
   using Cutlass3xGemmK8192 = typename sm90_fp8_config_K8192<
       InType, OutType, vllm::c3x::ScaledEpilogueArray>::Cutlass3xGemm;
-  using Cutlass3xGemmM16 = typename sm90_fp8_config_M16<
+  using Cutlass3xGemmM4 = typename sm90_fp8_config_M4<
+      InType, OutType, vllm::c3x::ScaledEpilogueArray>::Cutlass3xGemm;
+  using Cutlass3xGemmM64 = typename sm90_fp8_config_M64<
       InType, OutType, vllm::c3x::ScaledEpilogueArray>::Cutlass3xGemm;
   using Cutlass3xGemmDefault = typename sm90_fp8_config_default<
       InType, OutType, vllm::c3x::ScaledEpilogueArray>::Cutlass3xGemm;
@@ -111,18 +130,24 @@ void run_cutlass_moe_mm_sm90(
   uint32_t const n = out_tensors.size(1);
   uint32_t const k = a_tensors.size(1);
 
-  if (n >= 8192) {
-    cutlass_group_gemm_caller<Cutlass3xGemmN8192>(
+  // Use swap_ab for M <= 64 by default to reduce padding
+  if (m <= 4) {
+    cutlass_group_gemm_caller<Cutlass3xGemmM4>(
         out_tensors, a_tensors, b_tensors, a_scales, b_scales, expert_offsets,
         problem_sizes, a_strides, b_strides, c_strides, per_act_token,
         per_out_ch);
-  } else if (k >= 8192) {
-    cutlass_group_gemm_caller<Cutlass3xGemmK8192>(
+  } else if (m <= 64) {
+    cutlass_group_gemm_caller<Cutlass3xGemmM64>(
         out_tensors, a_tensors, b_tensors, a_scales, b_scales, expert_offsets,
         problem_sizes, a_strides, b_strides, c_strides, per_act_token,
         per_out_ch);
-  } else if (m <= 16) {
-    cutlass_group_gemm_caller<Cutlass3xGemmM16>(
+  } else if (n >= 8192) {
+    cutlass_group_gemm_caller<Cutlass3xGemmN8192>(
+        out_tensors, a_tensors, b_tensors, a_scales, b_scales, expert_offsets,
+        problem_sizes, a_strides, b_strides, c_strides, per_act_token,
+        per_out_ch);
+  } else if (k >= 8192) {
+    cutlass_group_gemm_caller<Cutlass3xGemmK8192>(
         out_tensors, a_tensors, b_tensors, a_scales, b_scales, expert_offsets,
         problem_sizes, a_strides, b_strides, c_strides, per_act_token,
         per_out_ch);
diff --git a/csrc/quantization/cutlass_w8a8/moe/grouped_mm_c3x.cuh b/csrc/quantization/cutlass_w8a8/moe/grouped_mm_c3x.cuh
@@ -22,24 +22,30 @@ using ArchTag = cutlass::arch::Sm90;
 using OperatorClass = cutlass::arch::OpClassTensorOp;
 
 using LayoutA = cutlass::layout::RowMajor;
+using LayoutA_Transpose =
+    typename cutlass::layout::LayoutTranspose<LayoutA>::type;
 using LayoutB = cutlass::layout::ColumnMajor;
-using LayoutC = cutlass::layout::RowMajor;
+using LayoutB_Transpose =
+    typename cutlass::layout::LayoutTranspose<LayoutB>::type;
+using LayoutD = cutlass::layout::RowMajor;
+using LayoutD_Transpose =
+    typename cutlass::layout::LayoutTranspose<LayoutD>::type;
+using LayoutC = LayoutD;
+using LayoutC_Transpose = LayoutD_Transpose;
 
 template <typename ElementAB_, typename ElementC_,
           template <typename, typename, typename> typename Epilogue_,
           typename TileShape, typename ClusterShape, typename KernelSchedule,
-          typename EpilogueSchedule>
+          typename EpilogueSchedule, bool swap_ab_ = false>
 struct cutlass_3x_group_gemm {
+  static constexpr bool swap_ab = swap_ab_;
   using ElementAB = ElementAB_;
   using ElementC = void;
   using ElementD = ElementC_;
   using ElementAccumulator = float;
 
   using Epilogue = Epilogue_<ElementAccumulator, ElementD, TileShape>;
 
-  using StrideC =
-      cute::remove_pointer_t<cute::Stride<int64_t, cute::Int<1>, cute::Int<0>>>;
-
   static constexpr int AlignmentAB =
       128 / cutlass::sizeof_bits<ElementAB>::value;
   static constexpr int AlignmentC = 128 / cutlass::sizeof_bits<ElementD>::value;
@@ -50,19 +56,26 @@ struct cutlass_3x_group_gemm {
       typename cutlass::epilogue::collective::CollectiveBuilder<
           ArchTag, OperatorClass, TileShape, ClusterShape,
           cutlass::epilogue::collective::EpilogueTileAuto, ElementAccumulator,
-          ElementAccumulator, ElementC, LayoutC*, AlignmentC, ElementD,
-          LayoutC*, AlignmentC, EpilogueSchedule, EVTCompute>::CollectiveOp;
+          ElementAccumulator, ElementC,
+          conditional_t<swap_ab, LayoutC_Transpose*, LayoutC*>, AlignmentC,
+          ElementD, conditional_t<swap_ab, LayoutD_Transpose*, LayoutD*>,
+          AlignmentC, EpilogueSchedule, EVTCompute>::CollectiveOp;
 
   static constexpr size_t CEStorageSize =
       sizeof(typename CollectiveEpilogue::SharedStorage);
   using Stages = typename cutlass::gemm::collective::StageCountAutoCarveout<
       static_cast<int>(CEStorageSize)>;
 
-  using CollectiveMainloop =
+  using CollectiveMainloop = conditional_t<
+      swap_ab,
+      typename cutlass::gemm::collective::CollectiveBuilder<
+          ArchTag, OperatorClass, ElementAB, LayoutB_Transpose*, AlignmentAB,
+          ElementAB, LayoutA_Transpose*, AlignmentAB, ElementAccumulator,
+          TileShape, ClusterShape, Stages, KernelSchedule>::CollectiveOp,
       typename cutlass::gemm::collective::CollectiveBuilder<
           ArchTag, OperatorClass, ElementAB, LayoutA*, AlignmentAB, ElementAB,
           LayoutB*, AlignmentAB, ElementAccumulator, TileShape, ClusterShape,
-          Stages, KernelSchedule>::CollectiveOp;
+          Stages, KernelSchedule>::CollectiveOp>;
 
   using KernelType = enable_sm90_only<cutlass::gemm::kernel::GemmUniversal<
       ProblemShape, CollectiveMainloop, CollectiveEpilogue>>;
@@ -78,12 +91,12 @@ void cutlass_group_gemm_caller(
     torch::Tensor const& problem_sizes, torch::Tensor const& a_strides,
     torch::Tensor const& b_strides, torch::Tensor const& c_strides,
     bool per_act_token, bool per_out_ch) {
+  static constexpr bool swap_ab = Gemm::swap_ab;
+
   using ElementAB = typename Gemm::ElementAB;
   using ElementD = typename Gemm::ElementD;
 
   int num_experts = static_cast<int>(expert_offsets.size(0));
-  int k_size = a_tensors.size(1);
-  int n_size = out_tensors.size(1);
 
   auto stream = at::cuda::getCurrentCUDAStream(a_tensors.device().index());
 
@@ -110,19 +123,35 @@ void cutlass_group_gemm_caller(
           problem_sizes.data_ptr());
   ProblemShape prob_shape{num_experts, problem_sizes_as_shapes, nullptr};
 
-  typename GemmKernel::MainloopArguments mainloop_args{
-      static_cast<const ElementAB**>(a_ptrs.data_ptr()),
-      static_cast<StrideA*>(a_strides.data_ptr()),
-      static_cast<const ElementAB**>(b_ptrs.data_ptr()),
-      static_cast<StrideB*>(b_strides.data_ptr())};
+  typename GemmKernel::MainloopArguments mainloop_args;
+  if constexpr (swap_ab) {
+    mainloop_args = typename GemmKernel::MainloopArguments{
+        static_cast<const ElementAB**>(b_ptrs.data_ptr()),
+        static_cast<StrideB*>(b_strides.data_ptr()),
+        static_cast<const ElementAB**>(a_ptrs.data_ptr()),
+        static_cast<StrideA*>(a_strides.data_ptr())};
+  } else {
+    mainloop_args = typename GemmKernel::MainloopArguments{
+        static_cast<const ElementAB**>(a_ptrs.data_ptr()),
+        static_cast<StrideA*>(a_strides.data_ptr()),
+        static_cast<const ElementAB**>(b_ptrs.data_ptr()),
+        static_cast<StrideB*>(b_strides.data_ptr())};
+  }
 
   // Currently, we are only able to do broadcast on either all or none a_scales
   // and on either all or none b_scales
   typename GemmKernel::EpilogueArguments epilogue_args{
       Gemm::Epilogue::prepare_args(
-          static_cast<const ElementAccumulator**>(a_scales_ptrs.data_ptr()),
-          static_cast<const ElementAccumulator**>(b_scales_ptrs.data_ptr()),
-          per_act_token, per_out_ch),
+          swap_ab ? static_cast<const ElementAccumulator**>(
+                        b_scales_ptrs.data_ptr())
+                  : static_cast<const ElementAccumulator**>(
+                        a_scales_ptrs.data_ptr()),
+          swap_ab ? static_cast<const ElementAccumulator**>(
+                        a_scales_ptrs.data_ptr())
+                  : static_cast<const ElementAccumulator**>(
+                        b_scales_ptrs.data_ptr()),
+          swap_ab ? per_out_ch : per_act_token,
+          swap_ab ? per_act_token : per_out_ch),
       nullptr, static_cast<StrideC*>(c_strides.data_ptr()),
       static_cast<ElementD**>(out_ptrs.data_ptr()),
       static_cast<StrideC*>(c_strides.data_ptr())};
diff --git a/csrc/quantization/cutlass_w8a8/moe/moe_data.cu b/csrc/quantization/cutlass_w8a8/moe/moe_data.cu
@@ -6,7 +6,10 @@
 #include <iostream>
 
 constexpr uint64_t THREADS_PER_EXPERT = 512;
+// threshold must match the dispatch logic in run_cutlass_moe_mm_sm90()
+constexpr int SWAP_AB_THRESHOLD = 64;
 
+template <bool SWAP_AB>
 __global__ void compute_problem_sizes(const int32_t* __restrict__ topk_ids,
                                       int32_t* problem_sizes1,
                                       int32_t* problem_sizes2,
@@ -24,40 +27,53 @@ __global__ void compute_problem_sizes(const int32_t* __restrict__ topk_ids,
 
   if (threadIdx.x == 0) {
     int final_occurrences = atomic_buffer[expert_id];
-    problem_sizes1[expert_id * 3] = final_occurrences;
-    problem_sizes1[expert_id * 3 + 1] = 2 * n;
-    problem_sizes1[expert_id * 3 + 2] = k;
-    problem_sizes2[expert_id * 3] = final_occurrences;
-    problem_sizes2[expert_id * 3 + 1] = k;
-    problem_sizes2[expert_id * 3 + 2] = n;
+    if constexpr (!SWAP_AB) {
+      problem_sizes1[expert_id * 3] = final_occurrences;
+      problem_sizes1[expert_id * 3 + 1] = 2 * n;
+      problem_sizes1[expert_id * 3 + 2] = k;
+      problem_sizes2[expert_id * 3] = final_occurrences;
+      problem_sizes2[expert_id * 3 + 1] = k;
+      problem_sizes2[expert_id * 3 + 2] = n;
+    } else {
+      problem_sizes1[expert_id * 3] = 2 * n;
+      problem_sizes1[expert_id * 3 + 1] = final_occurrences;
+      problem_sizes1[expert_id * 3 + 2] = k;
+      problem_sizes2[expert_id * 3] = k;
+      problem_sizes2[expert_id * 3 + 1] = final_occurrences;
+      problem_sizes2[expert_id * 3 + 2] = n;
+    }
   }
 }
 
 __global__ void compute_expert_offsets(
     const int32_t* __restrict__ problem_sizes1, int32_t* expert_offsets,
-    int32_t* atomic_buffer, const int num_experts) {
+    int32_t* atomic_buffer, const int num_experts, const int topk_length) {
   int32_t tot_offset = 0;
   expert_offsets[0] = 0;
   for (int i = 0; i < num_experts; ++i) {
     atomic_buffer[i] = tot_offset;
-    tot_offset += problem_sizes1[i * 3];
+    tot_offset += topk_length > SWAP_AB_THRESHOLD ? problem_sizes1[i * 3]
+                                                  : problem_sizes1[i * 3 + 1];
     expert_offsets[i + 1] = tot_offset;
   }
 }
 
 __global__ void compute_expert_blockscale_offsets(
     const int32_t* __restrict__ problem_sizes1, int32_t* expert_offsets,
-    int32_t* blockscale_offsets, int32_t* atomic_buffer,
-    const int num_experts) {
+    int32_t* blockscale_offsets, int32_t* atomic_buffer, const int num_experts,
+    const int topk_length) {
   int32_t tot_offset = 0;
   int32_t tot_offset_round = 0;
   expert_offsets[0] = 0;
   blockscale_offsets[0] = 0;
   for (int i = 0; i < num_experts; ++i) {
+    int32_t cur_offset = topk_length > SWAP_AB_THRESHOLD
+                             ? problem_sizes1[i * 3]
+                             : problem_sizes1[i * 3 + 1];
     atomic_buffer[i] = tot_offset;
-    tot_offset += problem_sizes1[i * 3];
+    tot_offset += cur_offset;
     expert_offsets[i + 1] = tot_offset;
-    tot_offset_round += (problem_sizes1[i * 3] + (128 - 1)) / 128 * 128;
+    tot_offset_round += (cur_offset + (128 - 1)) / 128 * 128;
     blockscale_offsets[i + 1] = tot_offset_round;
   }
 }
@@ -102,22 +118,36 @@ void get_cutlass_moe_mm_data_caller(
   torch::Tensor atomic_buffer = torch::zeros(num_experts, options_int32);
 
   int num_threads = min(THREADS_PER_EXPERT, topk_ids.numel());
-  compute_problem_sizes<<<num_experts, num_threads, 0, stream>>>(
-      static_cast<const int32_t*>(topk_ids.data_ptr()),
-      static_cast<int32_t*>(problem_sizes1.data_ptr()),
-      static_cast<int32_t*>(problem_sizes2.data_ptr()),
-      static_cast<int32_t*>(atomic_buffer.data_ptr()), topk_ids.numel(), n, k);
+
+  if (topk_ids.numel() > SWAP_AB_THRESHOLD) {
+    compute_problem_sizes<false><<<num_experts, num_threads, 0, stream>>>(
+        static_cast<const int32_t*>(topk_ids.data_ptr()),
+        static_cast<int32_t*>(problem_sizes1.data_ptr()),
+        static_cast<int32_t*>(problem_sizes2.data_ptr()),
+        static_cast<int32_t*>(atomic_buffer.data_ptr()), topk_ids.numel(), n,
+        k);
+  } else {
+    compute_problem_sizes<true><<<num_experts, num_threads, 0, stream>>>(
+        static_cast<const int32_t*>(topk_ids.data_ptr()),
+        static_cast<int32_t*>(problem_sizes1.data_ptr()),
+        static_cast<int32_t*>(problem_sizes2.data_ptr()),
+        static_cast<int32_t*>(atomic_buffer.data_ptr()), topk_ids.numel(), n,
+        k);
+  }
+
   if (blockscale_offsets.has_value()) {
     compute_expert_blockscale_offsets<<<1, 1, 0, stream>>>(
         static_cast<const int32_t*>(problem_sizes1.data_ptr()),
         static_cast<int32_t*>(expert_offsets.data_ptr()),
         static_cast<int32_t*>(blockscale_offsets.value().data_ptr()),
-        static_cast<int32_t*>(atomic_buffer.data_ptr()), num_experts);
+        static_cast<int32_t*>(atomic_buffer.data_ptr()), num_experts,
+        topk_ids.numel());
   } else {
     compute_expert_offsets<<<1, 1, 0, stream>>>(
         static_cast<const int32_t*>(problem_sizes1.data_ptr()),
         static_cast<int32_t*>(expert_offsets.data_ptr()),
-        static_cast<int32_t*>(atomic_buffer.data_ptr()), num_experts);
+        static_cast<int32_t*>(atomic_buffer.data_ptr()), num_experts,
+        topk_ids.numel());
   }
   compute_arg_sorts<<<num_experts, num_threads, 0, stream>>>(
       static_cast<const int32_t*>(topk_ids.data_ptr()),
diff --git a/tests/kernels/moe/test_cutlass_moe.py b/tests/kernels/moe/test_cutlass_moe.py
@@ -25,6 +25,7 @@
     (2, 1024, 1536),
     (2, 3072, 1024),
     (2, 3072, 1536),
+    (7, 3072, 1536),
     (64, 1024, 1024),
     (64, 1024, 1536),
     (64, 3072, 1024),
