Enable preshuffled mixed dtype Cutlass Gemm (pytorch#3722)

jwfromm · facebook-github-bot · commit dc741e7b4ded · 2025-02-21T15:54:49.000-08:00
Summary:

WIP to enable new optimized preshuffled fp8xint4 gemm.

While the example compiles and runs, it runs into a variety of problems. The outputs are either completely incorrect, contain NaNs, or the kernel hits an Illegal Memory Access. I'm not yet sure why.

Differential Revision: D69955197
diff --git a/fbgemm_gpu/experimental/gen_ai/bench/quantize_ops.py b/fbgemm_gpu/experimental/gen_ai/bench/quantize_ops.py
@@ -1121,6 +1121,54 @@ def cuda(self) -> bool:
         return True
 
 
+@register_quantize_op
+class F8I4ShuffledGemm(F8I4RowwiseGemm):
+    def _int4_row_quantize(
+        self,
+        x: torch.Tensor,
+        group_size: int = 128,
+    ) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
+        n_bit = 4  # Number of target bits.
+        to_quant = x.reshape(-1, group_size).to(torch.float)
+
+        max_val = torch.abs(to_quant).amax(dim=1, keepdim=True)
+        max_int = 2 ** (n_bit - 1)
+        min_int = -(2 ** (n_bit - 1))
+        scales = max_val.clamp(min=1e-6) / max_int
+
+        out = to_quant.div(scales).round().clamp_(min_int, max_int - 1)
+
+        # Cast to int8 and restore shape.
+        out = out.to(dtype=torch.int8).reshape(x.shape)
+
+        # View scales as rows, groups.
+        scales = scales.view(x.shape[0], -1)
+
+        return out, scales
+
+    def quantize(self, x, w):
+        # Quantize both input tensors.
+        xq, x_scale = quantize_fp8_row(x)
+        wq, w_scale = self._int4_row_quantize(w)
+        # Pack int4 values together.
+        wq = self._pack_int4(wq)
+        # Shuffle weights and scales for faster compute.
+        wq, w_scale = torch.ops.fbgemm.preshuffle_i4(wq, w_scale)
+        return xq, wq, x_scale, w_scale
+
+    def compute(self, xq, wq, x_scale, w_scale):
+        out = torch.ops.fbgemm.f8i4bf16_shuffled(xq, wq, x_scale, w_scale)
+        return out
+
+    def quantize_and_compute(self, x, w):
+        xq, wq, x_scale, w_scale = self.quantize(x, w)
+        return self.compute(xq, wq, x_scale, w_scale)
+
+    @property
+    def name(self) -> str:
+        return "cutlass_f8i4_preshuffle"
+
+
 @register_quantize_op
 class BF16I4RowwiseGemm(F8I4RowwiseGemm):
     """
diff --git a/fbgemm_gpu/experimental/gen_ai/src/quantize/cutlass_extensions/f8i4bf16_shuffled.cu b/fbgemm_gpu/experimental/gen_ai/src/quantize/cutlass_extensions/f8i4bf16_shuffled.cu
@@ -0,0 +1,254 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <ATen/ATen.h>
+#include <ATen/cuda/CUDAContext.h>
+
+#include "cutlass/cutlass.h"
+
+#include "cute/tensor.hpp"
+#include "cutlass/epilogue/collective/collective_builder.hpp"
+#include "cutlass/epilogue/collective/default_epilogue.hpp"
+#include "cutlass/epilogue/thread/linear_combination.h"
+#include "cutlass/gemm/collective/collective_builder.hpp"
+#include "cutlass/gemm/device/gemm_universal_adapter.h"
+#include "cutlass/gemm/dispatch_policy.hpp"
+#include "cutlass/gemm/kernel/gemm_universal.hpp"
+#include "cutlass/tensor_ref.h"
+
+#include "cutlass/util/mixed_dtype_utils.hpp"
+#include "cutlass/util/packed_stride.hpp"
+
+namespace fbgemm_gpu {
+
+at::Tensor f8i4bf16_shuffled(
+    at::Tensor XQ,
+    at::Tensor WQ,
+    at::Tensor x_scale,
+    at::Tensor w_scale) {
+  // Get shape information from input tensors.
+  int M = XQ.size(0);
+  int K = XQ.size(1);
+  int N = WQ.size(0);
+  int num_groups = w_scale.size(1);
+  int group_size = K / num_groups;
+  // Allocate output.
+  at::Tensor Y = at::empty({M, N}, XQ.options().dtype(at::kBFloat16));
+
+  // Define input types.
+  using MmaType = cutlass::float_e4m3_t;
+  using QuantType = cutlass::int4b_t;
+  constexpr int TileShapeK = 128 * 8 / cute::sizeof_bits<MmaType>::value;
+
+  // A Matrix configuration.
+  using ElementA = MmaType;
+  using LayoutA = cutlass::layout::RowMajor;
+  constexpr int AlignmentA = 128 / cutlass::sizeof_bits<ElementA>::value;
+
+  // B Matrix Configuration.
+  using ElementB = QuantType;
+  using LayoutB = cutlass::layout::ColumnMajor;
+  constexpr int AlignmentB = 128 / cutlass::sizeof_bits<ElementB>::value;
+
+  // We need to manually swap and transpose inputs. Unclear how required this is
+  // though.
+  using LayoutA_Transpose =
+      typename cutlass::layout::LayoutTranspose<LayoutA>::type;
+  using LayoutB_Transpose =
+      typename cutlass::layout::LayoutTranspose<LayoutB>::type;
+
+  using StrideA = cutlass::detail::TagToStrideA_t<LayoutA>;
+  using StrideB = cutlass::detail::TagToStrideB_t<LayoutB>;
+
+  // Define layout for shuffled weight tensor.
+  using LayoutAtomQuant =
+      decltype(cutlass::compute_memory_reordering_atom<MmaType>());
+  using LayoutB_Reordered = decltype(cute::tile_to_shape(
+      LayoutAtomQuant{}, cute::Layout<cute::Shape<int, int, int>, StrideB>{}));
+
+  using ElementScale = MmaType;
+  using LayoutScale = cutlass::layout::RowMajor;
+
+  // Output Matrix configuration.
+  using ElementC = cutlass::bfloat16_t;
+  using LayoutC = cutlass::layout::RowMajor;
+  constexpr int AlignmentC = 128 / cutlass::sizeof_bits<ElementC>::value;
+
+  // Core kernel configurations
+  using ElementAccumulator = float;
+  using ElementCompute = float;
+  using ArchTag = cutlass::arch::Sm90;
+  using OperatorClass = cutlass::arch::OpClassTensorOp;
+  // TODO tune these shapes.
+  using TileShape = cute::Shape<cute::_128, cute::_128, cute::Int<TileShapeK>>;
+  using ClusterShape = cute::Shape<cute::_1, cute::_1, cute::_1>;
+  // TODO Should we use fast accum here?
+  using KernelSchedule = cutlass::gemm::KernelTmaWarpSpecializedCooperative;
+  // Might be the only epilogue schedule that supports swap + transpose.
+  using EpilogueSchedule = cutlass::epilogue::TmaWarpSpecializedCooperative;
+  using EpilogueTileType = cutlass::epilogue::collective::EpilogueTileAuto;
+
+  // Define EVT for rowwise scaling.
+  using XScale = cutlass::epilogue::fusion::Sm90RowBroadcast<
+      0,
+      TileShape,
+      ElementAccumulator,
+      ElementAccumulator,
+      cute::Stride<cute::Int<0>, cute::Int<1>, cute::Int<0>>>;
+
+  using Accum = cutlass::epilogue::fusion::Sm90AccFetch;
+
+  using Compute0 = cutlass::epilogue::fusion::Sm90Compute<
+      cutlass::multiplies,
+      ElementC, // First stage output type.
+      ElementAccumulator, // First stage input types.
+      cutlass::FloatRoundStyle::round_to_nearest>;
+
+  using EpilogueEVT =
+      cutlass::epilogue::fusion::Sm90EVT<Compute0, XScale, Accum>;
+
+  using CollectiveEpilogue =
+      typename cutlass::epilogue::collective::CollectiveBuilder<
+          cutlass::arch::Sm90,
+          cutlass::arch::OpClassTensorOp,
+          TileShape,
+          ClusterShape,
+          EpilogueTileType,
+          ElementAccumulator,
+          ElementAccumulator,
+          ElementC,
+          typename cutlass::layout::LayoutTranspose<LayoutC>::type,
+          AlignmentC,
+          ElementC,
+          typename cutlass::layout::LayoutTranspose<LayoutC>::type,
+          AlignmentC,
+          EpilogueSchedule,
+          EpilogueEVT>::CollectiveOp;
+
+  using CollectiveMainloopScaleOnly =
+      typename cutlass::gemm::collective::CollectiveBuilder<
+          ArchTag,
+          OperatorClass,
+          cute::tuple<ElementB, cutlass::Array<ElementScale, 8>>,
+          LayoutB_Transpose,
+          AlignmentB,
+          ElementA,
+          LayoutA_Transpose,
+          AlignmentA,
+          ElementAccumulator,
+          TileShape,
+          ClusterShape,
+          cutlass::gemm::collective::StageCountAutoCarveout<static_cast<int>(
+              sizeof(typename CollectiveEpilogue::SharedStorage))>,
+          KernelSchedule>::CollectiveOp;
+
+  using GemmKernelScaleOnly = cutlass::gemm::kernel::GemmUniversal<
+      cute::Shape<int, int, int, int>, // Indicates ProblemShape
+      CollectiveMainloopScaleOnly,
+      CollectiveEpilogue>;
+
+  using CollectiveMainloopShuffled =
+      typename cutlass::gemm::collective::CollectiveBuilder<
+          ArchTag,
+          OperatorClass,
+          cute::tuple<ElementB, cutlass::Array<ElementScale, 8>>,
+          LayoutB_Reordered,
+          AlignmentB,
+          ElementA,
+          LayoutA_Transpose,
+          AlignmentA,
+          ElementAccumulator,
+          TileShape,
+          ClusterShape,
+          cutlass::gemm::collective::StageCountAutoCarveout<static_cast<int>(
+              sizeof(typename CollectiveEpilogue::SharedStorage))>,
+          KernelSchedule>::CollectiveOp;
+
+  using GemmKernelShuffled = cutlass::gemm::kernel::GemmUniversal<
+      cute::Shape<int, int, int, int>,
+      CollectiveMainloopShuffled,
+      CollectiveEpilogue>;
+
+  using GemmScaleOnly =
+      cutlass::gemm::device::GemmUniversalAdapter<GemmKernelScaleOnly>;
+  using GemmShuffled =
+      cutlass::gemm::device::GemmUniversalAdapter<GemmKernelShuffled>;
+
+  using StrideC = typename GemmKernelScaleOnly::StrideC;
+
+  /// Initialization
+  auto shape_B = cute::make_shape(N, K, 1);
+  StrideA stride_A =
+      cutlass::make_cute_packed_stride(StrideA{}, cute::make_shape(M, K, 1));
+  StrideB stride_B = cutlass::make_cute_packed_stride(StrideB{}, shape_B);
+  StrideC stride_C =
+      cutlass::make_cute_packed_stride(StrideC{}, cute::make_shape(N, M, 1));
+  LayoutB_Reordered layout_B_reordered =
+      cute::tile_to_shape(LayoutAtomQuant{}, shape_B);
+  using StrideS = typename CollectiveMainloopScaleOnly::StrideScale;
+  StrideS stride_S = cutlass::make_cute_packed_stride(
+      StrideS{}, cute::make_shape(N, num_groups, 1));
+
+  // Define Gemm arguments.
+  typename GemmShuffled::Arguments arguments{
+      cutlass::gemm::GemmUniversalMode::kGemm,
+      {N, M, K, 1},
+      {reinterpret_cast<ElementB*>(WQ.data_ptr()),
+       layout_B_reordered,
+       reinterpret_cast<ElementA*>(XQ.data_ptr()),
+       stride_A,
+       reinterpret_cast<cutlass::Array<ElementScale, 8>*>(w_scale.data_ptr()),
+       stride_S,
+       group_size},
+      {{},
+       reinterpret_cast<ElementC*>(Y.data_ptr()),
+       stride_C,
+       reinterpret_cast<ElementC*>(Y.data_ptr()),
+       stride_C}};
+
+  arguments.epilogue.thread = {
+      {reinterpret_cast<ElementAccumulator*>(x_scale.data_ptr())}, // x_scale
+      {}, // Accumulator
+      {}, // Multiplies
+  };
+
+  // Launch the workload.
+  GemmShuffled gemm;
+
+  // Using the arguments, query for extra workspace required for matrix
+  // multiplication computation
+  size_t workspace_size = GemmShuffled::get_workspace_size(arguments);
+
+  // Allocate workspace memory
+  cutlass::device_memory::allocation<uint8_t> workspace(workspace_size);
+
+  // Check the problem size is supported or not
+  cutlass::Status status = gemm.can_implement(arguments);
+  if (status != cutlass::Status::kSuccess) {
+    throw std::runtime_error("cutlass cannot implement");
+  }
+
+  // Initialize CUTLASS kernel with arguments and workspace pointer
+  status = gemm.initialize(arguments, workspace.get());
+  if (status != cutlass::Status::kSuccess) {
+    throw std::runtime_error("cutlass cannot initialize");
+  }
+
+  status = gemm(at::cuda::getCurrentCUDAStream());
+
+  if (status != cutlass::Status::kSuccess) {
+    throw std::runtime_error(
+        std::string("cutlass cannot run") +
+        cutlass::cutlassGetStatusString(status));
+  }
+  C10_CUDA_KERNEL_LAUNCH_CHECK();
+
+  return Y;
+}
+
+} // namespace fbgemm_gpu
diff --git a/fbgemm_gpu/experimental/gen_ai/src/quantize/cutlass_extensions/mixed_dtype_utils.cu b/fbgemm_gpu/experimental/gen_ai/src/quantize/cutlass_extensions/mixed_dtype_utils.cu
@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <ATen/ATen.h>
+#include <ATen/cuda/CUDAContext.h>
+
+#include "cute/layout.hpp"
+#include "cutlass/detail/layout.hpp"
+#include "cutlass/layout/matrix.h"
+#include "cutlass/util/mixed_dtype_utils.hpp"
+
+namespace fbgemm_gpu {
+
+std::tuple<at::Tensor, at::Tensor> preshuffle_i4(
+    at::Tensor WQ,
+    at::Tensor w_scale) {
+  // Check that w_scale is proper type. if not, quantize it.
+  if (w_scale.dtype() != at::kFloat8_e4m3fn) {
+    TORCH_WARN(
+        "Weight scale must be FP8 for preshuffled GEMM. Performing downcasting.");
+    w_scale = w_scale.to(WQ.options().dtype(at::kFloat8_e4m3fn));
+  }
+  // Start by allocating space for shuffled tensors.
+  at::Tensor WQ_shuffled = at::empty_like(WQ);
+  at::Tensor w_scale_packed = at::empty_like(w_scale);
+  // WQ has two int4 values packed into each int8 dtype, so the size
+  // is larger than it seems.
+  size_t WQ_size = 2 * WQ.numel();
+  // Encode weights to enable efficient lookup.
+  cutlass::unified_encode_int4b(
+      reinterpret_cast<cutlass::int4b_t*>(WQ.data_ptr()),
+      reinterpret_cast<cutlass::int4b_t*>(WQ_shuffled.data_ptr()),
+      WQ_size);
+
+  // Pack scale values. Size is divided by 8 to account for packing.
+  size_t w_scale_size = w_scale.numel() / 8;
+  cutlass::pack_scale_fp8(
+      reinterpret_cast<cutlass::float_e4m3_t*>(w_scale.data_ptr()),
+      reinterpret_cast<cutlass::Array<cutlass::float_e4m3_t, 8>*>(
+          w_scale_packed.data_ptr()),
+      w_scale_size);
+
+  // Next we need to shuffle B. To do this, we define a few helper objects.
+  const int N = WQ.size(0);
+  const int K = 2 * WQ.size(1);
+  auto shape_B = cute::make_shape(N, K, 1);
+  using LayoutB = cutlass::layout::ColumnMajor;
+  using StrideB = cutlass::detail::TagToStrideB_t<LayoutB>;
+  using LayoutAtomQuant = decltype(cutlass::compute_memory_reordering_atom<
+                                   cutlass::float_e4m3_t>());
+  using LayoutB_Reordered = decltype(cute::tile_to_shape(
+      LayoutAtomQuant{}, cute::Layout<cute::Shape<int, int, int>, StrideB>{}));
+  StrideB stride_B;
+  auto layout_B = make_layout(shape_B, stride_B);
+  LayoutB_Reordered layout_B_reordered =
+      cute::tile_to_shape(LayoutAtomQuant{}, shape_B);
+  ;
+
+  // Now we're ready to reorder the tensor into proper layout.
+  cutlass::reorder_tensor(
+      reinterpret_cast<cutlass::int4b_t*>(WQ_shuffled.data_ptr()),
+      layout_B,
+      layout_B_reordered);
+
+  // Tensors should now be preshuffled and ready for use.
+  return {WQ_shuffled, w_scale_packed};
+}
+
+} // namespace fbgemm_gpu
diff --git a/fbgemm_gpu/experimental/gen_ai/src/quantize/quantize.cpp b/fbgemm_gpu/experimental/gen_ai/src/quantize/quantize.cpp
