fmha.hpp

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/*!
  \file
  \brief An universal device layer for cutlass 3.x-style kernels.
*/

#pragma once

// common
#include "cutlass/cutlass.h"
#include "cutlass/device_kernel.h"

#if !defined(__CUDACC_RTC__)
#include "cutlass/cluster_launch.hpp"
#include "cutlass/trace.h"
#endif // !defined(__CUDACC_RTC__)

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

namespace cutlass::fmha::device {

////////////////////////////////////////////////////////////////////////////////
////////////////////////////// CUTLASS 3.x API /////////////////////////////////
////////////////////////////////////////////////////////////////////////////////

template <class Kernel_>
class FMHA {
public:
  using Kernel = Kernel_;

  static int const kThreadCount = Kernel::MaxThreadsPerBlock;

  /// Argument structure: User API
  using Arguments = typename Kernel::Arguments;
  /// Argument structure: Kernel API
  using Params = typename Kernel::Params;

private:

  /// Kernel API parameters object
  Params params_;

  bool is_initialized(bool set = false) {
    static bool initialized = false;
    if (set) initialized = true;
    return initialized;
  }

public:

  /// Access the Params structure
  Params const& params() const {
    return params_;
  }

  /// Determines whether the GEMM can execute the given problem.
  static Status
  can_implement(Arguments const& args) {
    if (Kernel::can_implement(args)) {
      return Status::kSuccess;
    }
    else {
      return Status::kInvalid;
    }
  }

  /// Gets the workspace size
  static size_t
  get_workspace_size(Arguments const& args) {
    size_t workspace_bytes = 0;
    workspace_bytes += Kernel::get_workspace_size(args);
    return workspace_bytes;
  }

  /// Computes the grid shape
  static dim3
  get_grid_shape(Params const& params) {
    return Kernel::get_grid_shape(params);
  }

  /// Computes the maximum number of active blocks per multiprocessor
  static int maximum_active_blocks(int /* smem_capacity */ = -1) {
    CUTLASS_TRACE_HOST("FMHA::maximum_active_blocks()");
    int max_active_blocks = -1;
    int smem_size = Kernel::SharedStorageSize;

    // first, account for dynamic smem capacity if needed
    cudaError_t result;
    if (smem_size >= (48 << 10)) {
      CUTLASS_TRACE_HOST("  Setting smem size to " << smem_size);
      result = cudaFuncSetAttribute(
          device_kernel<Kernel>,
          cudaFuncAttributeMaxDynamicSharedMemorySize,
          smem_size);
      if (cudaSuccess != result) {
        result = cudaGetLastError(); // to clear the error bit
        CUTLASS_TRACE_HOST(
          "  cudaFuncSetAttribute() returned error: "
          << cudaGetErrorString(result));
        return -1;
      }
    }

    // query occupancy after setting smem size
    result = cudaOccupancyMaxActiveBlocksPerMultiprocessor(
        &max_active_blocks,
        device_kernel<Kernel>,
        Kernel::MaxThreadsPerBlock,
        smem_size);

    if (cudaSuccess != result) {
      result = cudaGetLastError(); // to clear the error bit
      CUTLASS_TRACE_HOST(
        "  cudaOccupancyMaxActiveBlocksPerMultiprocessor() returned error: "
        << cudaGetErrorString(result));
      return -1;
    }

    CUTLASS_TRACE_HOST("  max_active_blocks: " << max_active_blocks);
    return max_active_blocks;
  }

  /// Initializes GEMM state from arguments.
  Status
  initialize(Arguments const& args, void* workspace = nullptr, cudaStream_t stream = nullptr) {
    CUTLASS_TRACE_HOST("FMHA::initialize() - workspace "
      << workspace << ", stream: " << (stream ? "non-null" : "null"));

    // Initialize the workspace
    Status status = Kernel::initialize_workspace(args, workspace, stream);
    if (status != Status::kSuccess) {
      return status;
    }

    // Initialize the Params structure
    params_ = Kernel::to_underlying_arguments(args, workspace);

    if (is_initialized()) return Status::kSuccess;

    // account for dynamic smem capacity if needed
    int smem_size = Kernel::SharedStorageSize;
    if (smem_size >= (48 << 10)) {
      CUTLASS_TRACE_HOST("  Setting smem size to " << smem_size);
      cudaError_t result = cudaFuncSetAttribute(
          device_kernel<Kernel>,
          cudaFuncAttributeMaxDynamicSharedMemorySize,
          smem_size);
      if (cudaSuccess != result) {
        result = cudaGetLastError(); // to clear the error bit
        CUTLASS_TRACE_HOST("  cudaFuncSetAttribute() returned error: " << cudaGetErrorString(result));
        return Status::kErrorInternal;
      }
    }

    is_initialized(true);

    return Status::kSuccess;
  }

  /// Update API is preserved in 3.0, but does not guarantee a lightweight update of params.
  Status
  update(Arguments const& args, void* workspace = nullptr) {
    CUTLASS_TRACE_HOST("FMHA()::update() - workspace: " << workspace);

    size_t workspace_bytes = get_workspace_size(args);
    if (workspace_bytes > 0 && nullptr == workspace) {
      return Status::kErrorWorkspaceNull;
    }

    params_ = Kernel::to_underlying_arguments(args, workspace);
    return Status::kSuccess;
  }

  /// Primary run() entry point API that is static allowing users to create and manage their own params.
  /// Supplied params struct must be construct by calling Kernel::to_underling_arguments()
  static Status
  run(Params& params, cudaStream_t stream = nullptr) {
    CUTLASS_TRACE_HOST("FMHA::run()");
    dim3 const block = Kernel::get_block_shape();
    dim3 const grid = get_grid_shape(params);

    // configure smem size and carveout
    int smem_size = Kernel::SharedStorageSize;

    Status launch_result;
    // Use extended launch API only for mainloops that use it
    if constexpr(Kernel::ArchTag::kMinComputeCapability >= 90) {
      dim3 cluster(cute::size<0>(typename Kernel::ClusterShape{}),
                   cute::size<1>(typename Kernel::ClusterShape{}),
                   cute::size<2>(typename Kernel::ClusterShape{}));
      void const* kernel = (void const*) device_kernel<Kernel>;
      void* kernel_params[] = {&params};
      launch_result = ClusterLauncher::launch(grid, cluster, block, smem_size, stream, kernel, kernel_params);
    }
    else {
      launch_result = Status::kSuccess;
      device_kernel<Kernel><<<grid, block, smem_size, stream>>>(params);
    }

    cudaError_t result = cudaGetLastError();
    if (cudaSuccess == result && Status::kSuccess == launch_result) {
      return Status::kSuccess;
    }
    else {
      CUTLASS_TRACE_HOST("  Kernel launch failed. Reason: " << result);
      return Status::kErrorInternal;
    }
  }

  //
  // Non-static launch overloads that first create and set the internal params struct of this kernel handle.
  //

  /// Launches the kernel after first constructing Params internal state from supplied arguments.
  Status
  run(Arguments const& args, void* workspace = nullptr, cudaStream_t stream = nullptr) {
    Status status = initialize(args, workspace, stream);
    if (Status::kSuccess == status) {
      status = run(params_, stream);
    }
    return status;
  }

  /// Launches the kernel after first constructing Params internal state from supplied arguments.
  Status
  operator()(Arguments const& args, void* workspace = nullptr, cudaStream_t stream = nullptr) {
    return run(args, workspace, stream);
  }

  /// Overload that allows a user to re-launch the same kernel without updating internal params struct.
  Status
  run(cudaStream_t stream = nullptr) {
    return run(params_, stream);
  }

  /// Overload that allows a user to re-launch the same kernel without updating internal params struct.
  Status
  operator()(cudaStream_t stream = nullptr) {
    return run(params_, stream);
  }
};

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

} // namespace cutlass::device

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