gemm_universal_with_visitor.h

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/*! \file
    \brief Gemm kernel with an epilogue defined under the epilogue visitor concept
*/

#pragma once

#include "cutlass/cutlass.h"
#include "cutlass/gemm/kernel/gemm_universal.h"

/////////////////////////////////////////////////////////////////////////////////////////////////

namespace cutlass {
namespace gemm {
namespace kernel {

/////////////////////////////////////////////////////////////////////////////////////////////////

// Gemm that compute the epilogue visitor functor
template <
  typename Mma,                  ///! Threadblock-scoped matrix multiply-accumulate
  typename Epilogue,             ///! Epilogue
  typename ThreadblockSwizzle_   ///! Threadblock swizzling function
>
class GemmWithEpilogueVisitor: public GemmUniversal<Mma, Epilogue, ThreadblockSwizzle_> {
public:

  using ThreadblockSwizzle = ThreadblockSwizzle_;

  using Base = GemmUniversal<Mma, Epilogue, ThreadblockSwizzle>;
  using Base::Base;

  using FusionCallbacks = typename Epilogue::FusionCallbacks;

  using ElementA = typename Base::ElementA;
  using LayoutA = typename Base::LayoutA;
  using ElementB = typename Base::ElementB;
  using LayoutB = typename Base::LayoutB;
  using ElementC = typename Base::ElementC;
  using LayoutC = typename Base::LayoutC;

  using ThreadblockShape = typename Mma::Shape;

  //
  // Structures
  //

  using SharedStorage = typename Base::SharedStorage;
  using Arguments = typename Base::Arguments;

  //
  // Structure for precomputing values in host memory and passing to kernels
  //

  /// Parameters structure
  struct Params : UniversalParamsBase<
    ThreadblockSwizzle,
    ThreadblockShape,
    ElementA,
    ElementB,
    ElementC,
    LayoutA,
    LayoutB>
  {
    using ParamsBase = UniversalParamsBase<
      ThreadblockSwizzle,
      ThreadblockShape,
      ElementA,
      ElementB,
      ElementC,
      LayoutA,
      LayoutB>;

    //
    // Data members
    //
    cute::Shape<int32_t,int32_t,int32_t> problem_shape;

    typename Mma::IteratorA::Params params_A;
    typename Mma::IteratorB::Params params_B;
    typename FusionCallbacks::Params output_op;

    void * ptr_A;
    void * ptr_B;

    int64_t batch_stride_A;
    int64_t batch_stride_B;

    int * ptr_gather_A_indices;
    int * ptr_gather_B_indices;

    //
    // Host dispatch API
    //

    /// Default constructor
    Params() = default;

    /// Constructor
    Params(
      Arguments const &args,  /// GEMM application arguments
      int device_sms,         /// Number of SMs on the device
      int sm_occupancy)       /// Kernel SM occupancy (in thread blocks)
    :
      ParamsBase(args, device_sms, sm_occupancy),
      params_A(args.lda ? make_Coord_with_padding<LayoutA::kStrideRank>(args.lda) : args.stride_a),
      params_B(args.ldb ? make_Coord_with_padding<LayoutB::kStrideRank>(args.ldb) : args.stride_b),
      output_op(FusionCallbacks::to_underlying_arguments(args.problem_size, args.epilogue, nullptr /*workspace*/)),
      problem_shape({args.problem_size.m(), args.problem_size.n(), args.batch_count}),
      ptr_A(const_cast<void *>(args.ptr_A)),
      ptr_B(const_cast<void *>(args.ptr_B)),
      batch_stride_A(args.batch_stride_A),
      batch_stride_B(args.batch_stride_B),
      ptr_gather_A_indices(const_cast<int *>(args.ptr_gather_A_indices)),
      ptr_gather_B_indices(const_cast<int *>(args.ptr_gather_B_indices))
    {
      // Raise error on unsupported modes
      assert(args.mode != GemmUniversalMode::kGemmSplitKParallel && "Sm80 EVT does not support SplitKParallel.");
      assert(!(args.mode == GemmUniversalMode::kGemm && this->grid_tiled_shape.k() > 1 )
        && "Sm80 EVT does not support SplitKSerial.");
      assert(args.mode != GemmUniversalMode::kArray && "Sm80 EVT does not support Array Gemm.");
    }

    /// Lightweight update given a subset of arguments.
    void update(Arguments const &args)
    {
      CUTLASS_TRACE_HOST("GemmUniversalwithVisitor::Params::update()");

      // Update input pointers
      ptr_A = const_cast<void *>(args.ptr_A);
      ptr_B = const_cast<void *>(args.ptr_B);

      batch_stride_A = args.batch_stride_A;
      batch_stride_B = args.batch_stride_B;
      this->batch_stride_D = args.batch_stride_D;

      ptr_gather_A_indices = const_cast<int *>(args.ptr_gather_A_indices);
      ptr_gather_B_indices = const_cast<int *>(args.ptr_gather_B_indices);

      output_op = FusionCallbacks::to_underlying_arguments(args.problem_size, args.epilogue, nullptr /*workspace*/);
      problem_shape = make_shape(args.problem_size.m(), args.problem_size.n(), args.batch_count);
    }
  };

public:

  //
  // Device-only API
  //

  // Factory invocation
  CUTLASS_DEVICE
  static void invoke(
    Params const &params,
    SharedStorage &shared_storage)
  {
    GemmWithEpilogueVisitor op;
    op(params, shared_storage);
  }


  /// Executes one GEMM
  CUTLASS_DEVICE
  void operator()(Params const &params, SharedStorage &shared_storage) {
    ThreadblockSwizzle threadblock_swizzle;
    run_with_swizzle(params, shared_storage, threadblock_swizzle);
  }

  /// Executes one GEMM with an externally-provided swizzling function
  CUTLASS_DEVICE
  void run_with_swizzle(Params const &params, SharedStorage &shared_storage, ThreadblockSwizzle& threadblock_swizzle) {

    cutlass::gemm::GemmCoord threadblock_tile_offset =
        threadblock_swizzle.get_tile_offset(params.swizzle_log_tile);

    // Early exit if CTA is out of range
    if (params.grid_tiled_shape.m() <= threadblock_tile_offset.m() ||
      params.grid_tiled_shape.n() <= threadblock_tile_offset.n()) {

      return;
    }

    int offset_k = 0;
    int problem_size_k = params.problem_size.k();

    ElementA *ptr_A = static_cast<ElementA *>(params.ptr_A); 
    ElementB *ptr_B = static_cast<ElementB *>(params.ptr_B);

    //
    // Fetch pointers based on mode.
    //
    if (params.mode == GemmUniversalMode::kGemm) {

      if (threadblock_tile_offset.k() + 1 < params.grid_tiled_shape.k()) {

        problem_size_k = (threadblock_tile_offset.k() + 1) * params.gemm_k_size; 
      }

      offset_k = threadblock_tile_offset.k() * params.gemm_k_size;
    }
    else if (params.mode == GemmUniversalMode::kBatched) {
      ptr_A += threadblock_tile_offset.k() * params.batch_stride_A;
      ptr_B += threadblock_tile_offset.k() * params.batch_stride_B;
    }

    __syncthreads();

    // Compute initial location in logical coordinates
    cutlass::MatrixCoord tb_offset_A{
      threadblock_tile_offset.m() * Mma::Shape::kM,
      offset_k,
    };

    cutlass::MatrixCoord tb_offset_B{
      offset_k,
      threadblock_tile_offset.n() * Mma::Shape::kN
    };

    // Compute position within threadblock
    int thread_idx = threadIdx.x;

    // Construct iterators to A and B operands
    typename Mma::IteratorA iterator_A(
      params.params_A,
      ptr_A,
      {params.problem_size.m(), problem_size_k},
      thread_idx,
      tb_offset_A,
      params.ptr_gather_A_indices);

    typename Mma::IteratorB iterator_B(
      params.params_B,
      ptr_B,
      {problem_size_k, params.problem_size.n()},
      thread_idx,
      tb_offset_B,
      params.ptr_gather_B_indices);

    // Broadcast the warp_id computed by lane 0 to ensure dependent code
    // is compiled as warp-uniform.
    int warp_idx = canonical_warp_idx_sync();

    int lane_idx = threadIdx.x % 32;

    //
    // Main loop
    //

    // Construct thread-scoped matrix multiply
    Mma mma(shared_storage.main_loop, thread_idx, warp_idx, lane_idx);

    typename Mma::FragmentC accumulators;

    accumulators.clear();

    // Compute threadblock-scoped matrix multiply-add
    int gemm_k_iterations = (problem_size_k - offset_k + Mma::Shape::kK - 1) / Mma::Shape::kK;

    // Compute threadblock-scoped matrix multiply-add
    mma(
      gemm_k_iterations, 
      accumulators, 
      iterator_A, 
      iterator_B, 
      accumulators);

    //
    // Epilogue
    //

    threadblock_tile_offset = threadblock_swizzle.get_tile_offset(params.swizzle_log_tile);

    Epilogue epilogue(
      params.output_op,
      shared_storage.epilogue, 
      thread_idx, 
      warp_idx, 
      lane_idx);

    // Execute the epilogue operator to update the destination tensor.
    epilogue(accumulators, threadblock_tile_offset, params.problem_shape, thread_idx); 
  }
};

/////////////////////////////////////////////////////////////////////////////////////////////////

} // namespace kernel
} // namespace gemm
} // namespace cutlass

/////////////////////////////////////////////////////////////////////////////////////////////////