gpuThreadUtils.hpp

/*
  Copyright 2024 SINTEF AS

  This file is part of the Open Porous Media project (OPM).

  OPM is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  OPM is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef OPM_GPU_THREAD_UTILS_HPP
#define OPM_GPU_THREAD_UTILS_HPP
#include <cstddef>
#include <cuda.h>
#include <cuda_runtime.h>
#include <opm/simulators/linalg/gpuistl/detail/gpu_safe_call.hpp>

/*
    This file provides some logic for handling how to choose the correct thread-block size
*/
namespace Opm::gpuistl::detail
{
constexpr inline size_t
getThreads([[maybe_unused]] size_t numberOfRows)
{
    return 1024;
}

inline size_t
getBlocks(size_t numberOfRows)
{
    const auto threads = getThreads(numberOfRows);
    return (numberOfRows + threads - 1) / threads;
}

// Kernel here is the function object of the cuda kernel
template <class Kernel>
inline int
getCudaRecomendedThreadBlockSize(Kernel k, int suggestedThrBlockSize = -1)
{
    if (suggestedThrBlockSize != -1) {
        return suggestedThrBlockSize;
    }
    int blockSize;
    int tmpGridSize;
    OPM_GPU_SAFE_CALL(cudaOccupancyMaxPotentialBlockSize(&tmpGridSize, &blockSize, k, 0, 0));
    return blockSize;
}

inline int
getNumberOfBlocks(int wantedThreads, int threadBlockSize)
{
    return (wantedThreads + threadBlockSize - 1) / threadBlockSize;
}

} // namespace Opm::gpuistl::detail

#endif