swap A/B and naive heuristic

IwakuraRein · IwakuraRein · commit 59d5e360a595 · 2025-05-24T14:26:52.000-07:00
Signed-off-by: Lain &lt;siyuanf@nvidia.com&gt;
diff --git a/csrc/quantization/cutlass_w8a8/c3x/scaled_mm_blockwise_sm100_fp8.cu b/csrc/quantization/cutlass_w8a8/c3x/scaled_mm_blockwise_sm100_fp8.cu
@@ -9,10 +9,6 @@ void cutlass_scaled_mm_blockwise_sm100_fp8(torch::Tensor& out,
                                            torch::Tensor const& b,
                                            torch::Tensor const& a_scales,
                                            torch::Tensor const& b_scales) {
-  TORCH_CHECK(
-      a.size(0) % 4 == 0,
-      "Input tensor must have a number of rows that is a multiple of 4. ",
-      "but got: ", a.size(0), " rows.");
   if (out.dtype() == torch::kBFloat16) {
     cutlass_gemm_blockwise_sm100_fp8_dispatch<cutlass::bfloat16_t>(
         out, a, b, a_scales, b_scales);
diff --git a/csrc/quantization/cutlass_w8a8/c3x/scaled_mm_blockwise_sm100_fp8_dispatch.cuh b/csrc/quantization/cutlass_w8a8/c3x/scaled_mm_blockwise_sm100_fp8_dispatch.cuh
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "cuda_utils.h"
 #include "cutlass/cutlass.h"
 #include "cutlass/numeric_types.h"
 
@@ -22,49 +23,49 @@ namespace vllm {
 
 using namespace cute;
 
-template <typename OutType, typename MmaTileShape, typename ScalesPerTile,
-          class ClusterShape, typename EpilogueScheduler,
-          typename MainloopScheduler>
+// clang-format off
+template <class OutType, int ScaleGranularityM,
+          int ScaleGranularityN, int ScaleGranularityK,
+          class MmaTileShape, class ClusterShape,
+          class EpilogueScheduler, class MainloopScheduler,
+          bool swap_ab_ = false>
 struct cutlass_3x_gemm_fp8_blockwise {
+  static constexpr bool swap_ab = swap_ab_;
   using ElementAB = cutlass::float_e4m3_t;
 
   using ElementA = ElementAB;
   using LayoutA = cutlass::layout::RowMajor;
+  using LayoutA_Transpose = typename cutlass::layout::LayoutTranspose<LayoutA>::type;
   static constexpr int AlignmentA = 128 / cutlass::sizeof_bits<ElementA>::value;
 
   using ElementB = ElementAB;
   using LayoutB = cutlass::layout::ColumnMajor;
+  using LayoutB_Transpose = typename cutlass::layout::LayoutTranspose<LayoutB>::type;
   static constexpr int AlignmentB = 128 / cutlass::sizeof_bits<ElementB>::value;
 
-  using ElementC = void;
   using ElementD = OutType;
   using LayoutD = cutlass::layout::RowMajor;
+  using LayoutD_Transpose = typename cutlass::layout::LayoutTranspose<LayoutD>::type;
   static constexpr int AlignmentD = 128 / cutlass::sizeof_bits<ElementD>::value;
 
+  using ElementC = void; // TODO: support bias
   using LayoutC = LayoutD;
+  using LayoutC_Transpose = LayoutD_Transpose;
   static constexpr int AlignmentC = AlignmentD;
 
   using ElementAccumulator = float;
   using ElementCompute = float;
   using ElementBlockScale = float;
 
-  // MMA and Cluster Tile Shapes
-  // Shape of the tile computed by tcgen05 MMA, could be across 2 SMs if Cluster
-  // Shape %2 == 0 using MmaTileShape_MNK = Shape<_128,_128,_128>;
-  static constexpr int ScaleMsPerTile = size<0>(ScalesPerTile{});
-  static constexpr int ScaleGranularityM =
-      size<0>(MmaTileShape{}) / ScaleMsPerTile;
-  static constexpr int ScaleGranularityN =
-      size<1>(MmaTileShape{}) / size<1>(ScalesPerTile{});
-  static constexpr int ScaleGranularityK =
-      size<2>(MmaTileShape{}) / size<2>(ScalesPerTile{});
-
-  // Shape of the threadblocks in a cluster
-  using ClusterShape_MNK = ClusterShape;
-
-  using ScaleConfig = cutlass::detail::Sm100BlockwiseScaleConfig<
-      ScaleGranularityM, ScaleGranularityN, ScaleGranularityK,
-      cute::UMMA::Major::MN, cute::UMMA::Major::K>;
+  using ScaleConfig = conditional_t<swap_ab,
+      cutlass::detail::Sm100BlockwiseScaleConfig<
+        ScaleGranularityM, ScaleGranularityN, ScaleGranularityK,
+        cute::UMMA::Major::K, cute::UMMA::Major::MN>,
+      cutlass::detail::Sm100BlockwiseScaleConfig<
+        ScaleGranularityM, ScaleGranularityN, ScaleGranularityK,
+        cute::UMMA::Major::MN, cute::UMMA::Major::K>>;
+
+  // layout_SFA and layout_SFB cannot be swapped since they are deduced.
   using LayoutSFA = decltype(ScaleConfig::deduce_layoutSFA());
   using LayoutSFB = decltype(ScaleConfig::deduce_layoutSFB());
 
@@ -73,7 +74,6 @@ struct cutlass_3x_gemm_fp8_blockwise {
 
   static constexpr auto RoundStyle = cutlass::FloatRoundStyle::round_to_nearest;
   using ElementScalar = float;
-  // clang-format off
   using DefaultOperation = cutlass::epilogue::fusion::LinearCombination<ElementD, ElementCompute, ElementC, ElementScalar, RoundStyle>;
   using CollectiveEpilogue = typename cutlass::epilogue::collective::CollectiveBuilder<
       ArchTag,
@@ -84,33 +84,47 @@ struct cutlass_3x_gemm_fp8_blockwise {
       ElementAccumulator,
       ElementCompute,
       ElementC,
-      LayoutC,
+      conditional_t<swap_ab, LayoutC_Transpose, LayoutC>,
       AlignmentC,
       ElementD,
-      LayoutD,
+      conditional_t<swap_ab, LayoutD_Transpose, LayoutD>,
       AlignmentD,
       EpilogueScheduler,
       DefaultOperation
   >::CollectiveOp;
  
   using StageCountType = cutlass::gemm::collective::StageCountAuto; 
-  using CollectiveMainloop = typename cutlass::gemm::collective::CollectiveBuilder<
-      ArchTag,
-      OperatorClass,
-      ElementA,
-      cute::tuple<LayoutA, LayoutSFA>,
-      AlignmentA,
-      ElementB,
-      cute::tuple<LayoutB, LayoutSFB>,
-      AlignmentB,
-      ElementAccumulator,
-      MmaTileShape,
-      ClusterShape,
-
+  using CollectiveMainloop = conditional_t<swap_ab,
+      typename cutlass::gemm::collective::CollectiveBuilder<
+          ArchTag,
+          OperatorClass,
+          ElementB,
+          cute::tuple<LayoutB_Transpose, LayoutSFA>,
+          AlignmentB,
+          ElementA,
+          cute::tuple<LayoutA_Transpose, LayoutSFB>,
+          AlignmentA,
+          ElementAccumulator,
+          MmaTileShape,
+          ClusterShape,
           cutlass::gemm::collective::StageCountAutoCarveout<static_cast<int>(sizeof(typename CollectiveEpilogue::SharedStorage))>,
-      MainloopScheduler
-  >::CollectiveOp;
-  // clang-format on
+          MainloopScheduler
+      >::CollectiveOp,
+      typename cutlass::gemm::collective::CollectiveBuilder<
+          ArchTag,
+          OperatorClass,
+          ElementA,
+          cute::tuple<LayoutA, LayoutSFA>,
+          AlignmentA,
+          ElementB,
+          cute::tuple<LayoutB, LayoutSFB>,
+          AlignmentB,
+          ElementAccumulator,
+          MmaTileShape,
+          ClusterShape,
+          cutlass::gemm::collective::StageCountAutoCarveout<static_cast<int>(sizeof(typename CollectiveEpilogue::SharedStorage))>,
+          MainloopScheduler
+      >::CollectiveOp>;
 
   using KernelType = enable_sm100_only<cutlass::gemm::kernel::GemmUniversal<
       Shape<int, int, int, int>, CollectiveMainloop, CollectiveEpilogue>>;
@@ -123,6 +137,7 @@ void cutlass_gemm_caller_blockwise(torch::Tensor& out, torch::Tensor const& a,
                                    torch::Tensor const& b,
                                    torch::Tensor const& a_scales,
                                    torch::Tensor const& b_scales) {
+  static constexpr bool swap_ab = Gemm::swap_ab;
   using GemmKernel = typename Gemm::GemmKernel;
   using StrideA = typename Gemm::GemmKernel::StrideA;
   using StrideB = typename Gemm::GemmKernel::StrideB;
@@ -136,7 +151,6 @@ void cutlass_gemm_caller_blockwise(torch::Tensor& out, torch::Tensor const& a,
   using ElementD = typename Gemm::ElementD;
 
   int32_t m = a.size(0), n = b.size(1), k = a.size(1);
-  auto prob_shape = cute::make_shape(m, n, k, 1);
 
   StrideA a_stride;
   StrideB b_stride;
@@ -146,21 +160,36 @@ void cutlass_gemm_caller_blockwise(torch::Tensor& out, torch::Tensor const& a,
   b_stride =
       cutlass::make_cute_packed_stride(StrideB{}, cute::make_shape(n, k, 1));
   c_stride =
-      cutlass::make_cute_packed_stride(StrideC{}, cute::make_shape(m, n, 1));
+      cutlass::make_cute_packed_stride(StrideC{}, swap_ab ? cute::make_shape(n, m, 1) : cute::make_shape(m, n, 1));
 
-  LayoutSFA layout_SFA =
+  LayoutSFA layout_SFA = swap_ab ? 
+      ScaleConfig::tile_atom_to_shape_SFA(make_shape(n, m, k, 1)) :
       ScaleConfig::tile_atom_to_shape_SFA(make_shape(m, n, k, 1));
-  LayoutSFB layout_SFB =
+  LayoutSFB layout_SFB = swap_ab ?
+      ScaleConfig::tile_atom_to_shape_SFB(make_shape(n, m, k, 1)) :
       ScaleConfig::tile_atom_to_shape_SFB(make_shape(m, n, k, 1));
 
   auto a_ptr = static_cast<ElementAB*>(a.data_ptr());
   auto b_ptr = static_cast<ElementAB*>(b.data_ptr());
   auto a_scales_ptr = static_cast<float*>(a_scales.data_ptr());
   auto b_scales_ptr = static_cast<float*>(b_scales.data_ptr());
 
-  typename GemmKernel::MainloopArguments mainloop_args{
-      a_ptr,        a_stride,   b_ptr,        b_stride,
-      a_scales_ptr, layout_SFA, b_scales_ptr, layout_SFB};
+  auto mainloop_args = [&](){
+    // layout_SFA and layout_SFB cannot be swapped since they are deduced.
+    if (swap_ab) {
+      return typename GemmKernel::MainloopArguments{
+          b_ptr,        b_stride,   a_ptr,        a_stride,
+          b_scales_ptr, layout_SFA, a_scales_ptr, layout_SFB
+      };
+    }
+    else {
+      return typename GemmKernel::MainloopArguments{
+          a_ptr,        a_stride,   b_ptr,        b_stride,
+          a_scales_ptr, layout_SFA, b_scales_ptr, layout_SFB
+      };
+    }
+  }();
+  auto prob_shape = swap_ab ? cute::make_shape(n, m, k, 1) : cute::make_shape(m, n, k, 1);
 
   auto c_ptr = static_cast<ElementD*>(out.data_ptr());
   typename GemmKernel::EpilogueArguments epilogue_args{
@@ -181,23 +210,71 @@ void cutlass_gemm_blockwise_sm100_fp8_dispatch(torch::Tensor& out,
   int sms;
   cudaDeviceGetAttribute(&sms, cudaDevAttrMultiProcessorCount, a.get_device());
 
-  auto should_use_2sm = [&sms](int m, int n, int tile1SM = 128) {
-    return std::ceil(static_cast<float>(m) / tile1SM) *
-               std::ceil(static_cast<float>(n) / tile1SM) >=
-           sms;
-  };
-  bool use_2sm = should_use_2sm(m, n);
-  if (use_2sm) {
-    cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
-        OutType, Shape<_256, _128, _128>, Shape<_256, _1, _1>,
-        Shape<_2, _2, _1>, cutlass::epilogue::TmaWarpSpecialized2Sm,
-        cutlass::gemm::KernelTmaWarpSpecializedBlockwise2SmSm100>>(
-        out, a, b, a_scales, b_scales);
+  constexpr int TILE_K = 128;
+  // TODO: better heuristics
+  bool swap_ab = (m < 16) || (m % 4 != 0);
+  bool use_tma_epilogue = (m * n) % 4 == 0;
+  if (!swap_ab) {
+    constexpr int TILE_N = 128;
+    int tile_m = 256;
+    if (cuda_utils::ceil_div(n, TILE_N) * cuda_utils::ceil_div(m, 64) <= sms) {
+      tile_m = 64;
+    }
+    else if (cuda_utils::ceil_div(n, TILE_N) * cuda_utils::ceil_div(m, 128) <= sms) {
+      tile_m = 128;
+    }
+    if (tile_m == 64) {
+      if (use_tma_epilogue) {
+        cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
+            OutType, 1, TILE_N, TILE_K, Shape<_64, Int<TILE_N>, Int<TILE_K>>,
+            Shape<_1, _1, _1>, cutlass::epilogue::TmaWarpSpecialized1Sm,
+            cutlass::gemm::KernelTmaWarpSpecializedBlockwise1SmSm100>>(
+            out, a, b, a_scales, b_scales);
+      } else {
+        cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
+            OutType, 1, TILE_N, TILE_K, Shape<_64, Int<TILE_N>, Int<TILE_K>>,
+            Shape<_1, _1, _1>, cutlass::epilogue::NoSmemWarpSpecialized1Sm,
+            cutlass::gemm::KernelTmaWarpSpecializedBlockwise1SmSm100>>(
+            out, a, b, a_scales, b_scales);
+      }
+    } else if (tile_m == 128) {
+      if (use_tma_epilogue) {
+        cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
+            OutType, 1, TILE_N, TILE_K, Shape<_128, Int<TILE_N>, Int<TILE_K>>,
+            Shape<_1, _1, _1>, cutlass::epilogue::TmaWarpSpecialized1Sm,
+            cutlass::gemm::KernelTmaWarpSpecializedBlockwise1SmSm100>>(
+            out, a, b, a_scales, b_scales);
+      } else {
+        cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
+            OutType, 1, TILE_N, TILE_K, Shape<_128, Int<TILE_N>, Int<TILE_K>>,
+            Shape<_1, _1, _1>, cutlass::epilogue::NoSmemWarpSpecialized1Sm,
+            cutlass::gemm::KernelTmaWarpSpecializedBlockwise1SmSm100>>(
+            out, a, b, a_scales, b_scales);
+      }
+    } else { // tile_m == 256
+      if (use_tma_epilogue) {
+          cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
+              OutType, 1, TILE_N, TILE_K, Shape<_256, Int<TILE_N>, Int<TILE_K>>,
+            Shape<_2, _1, _1>, cutlass::epilogue::TmaWarpSpecialized2Sm,
+            cutlass::gemm::KernelTmaWarpSpecializedBlockwise2SmSm100>>(
+            out, a, b, a_scales, b_scales);
+      } else {
+          cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
+              OutType, 1, TILE_N, TILE_K, Shape<_256, Int<TILE_N>, Int<TILE_K>>,
+            Shape<_2, _1, _1>, cutlass::epilogue::NoSmemWarpSpecialized2Sm,
+            cutlass::gemm::KernelTmaWarpSpecializedBlockwise2SmSm100>>(
+            out, a, b, a_scales, b_scales);
+      }
+    }
   } else {
+    // TODO: Test more tile N configs
+    constexpr int TILE_M = 128;
+    constexpr int TILE_N = 16;
+    // TMA epilogue isn't compatible with Swap A/B
     cutlass_gemm_caller_blockwise<cutlass_3x_gemm_fp8_blockwise<
-        OutType, Shape<_128, _128, _128>, Shape<_128, _1, _1>,
-        Shape<_1, _1, _1>, cutlass::epilogue::TmaWarpSpecialized1Sm,
-        cutlass::gemm::KernelTmaWarpSpecializedBlockwise1SmSm100>>(
+        OutType, TILE_M, 1, TILE_K, Shape<Int<TILE_M>, Int<TILE_N>, Int<TILE_K>>,
+        Shape<_1, _1, _1>, cutlass::epilogue::NoSmemWarpSpecialized1Sm,
+        cutlass::gemm::KernelTmaWarpSpecializedBlockwise1SmSm100, true>>(
         out, a, b, a_scales, b_scales);
   }
 }
diff --git a/vllm/model_executor/layers/quantization/utils/fp8_utils.py b/vllm/model_executor/layers/quantization/utils/fp8_utils.py
@@ -135,24 +135,10 @@ def ceil_div(x: int, y: int) -> int:
         use_cutlass, use_aiter_and_is_supported)
 
     if use_cutlass:
-        rows, cols = input_2d.shape
-        # Blackwell GPUs (SM100) require row dimensions to be multiple of 4 for
-        # optimal tensor core usage. Can be removed when targeting platforms
-        # without this constraint.
-        should_pad = current_platform.has_device_capability(
-            100) and rows % 4 != 0
-        if should_pad:
-            input_2d = torch.nn.functional.pad(input_2d,
-                                               (0, 0, 0, 4 - (rows % 4)),
-                                               value=0).contiguous()
-
         q_input, x_scale = per_token_group_quant_fp8(
             input_2d, block_size[1], column_major_scales=use_cutlass)
-
         output = w8a8_blockscale_func(q_input, weight, x_scale, weight_scale,
                                       block_size, input.dtype)
-        if should_pad:
-            output = output[:rows, :]
 
     else:
         q_input, x_scale = per_token_group_quant_fp8(
