c++ - 为什么 OpenCL 无法将 enqueueReadBuffer 放入二维 vector 中？

Question

我不确定这是一个错误，还是我只是犯了一个简单的错误，但将 OpenCL 缓冲区读入二维 vector 似乎会导致一些奇怪的行为。

我的意思是，在调用 queue.enqueueReadBuffer 之后，它会出现段错误或崩溃，并出现诸如“损坏的双链表”或“free():无效大小”之类的消息。如果有帮助，我可以提供回溯/内存映射。

读入一维 vector 按预期工作。

我正在使用 AMD Catalyst 13.25.5 运行 Linux 3.8.0-35 (x86_64)，我使用以下代码编译它:g++ -I/opt/AMDAPP/include main.cpp OpenCl.cpp -lOpenCL

最小工作示例:

main.cpp

// System headers
#include <iostream>
#include <vector>

// Third-party headers
#include <CL/cl.hpp>

// Project headers
#include "OpenCl.h"

int main(int argc, char* argv[])
{
    OpenCl opencl;

    const unsigned int num_rows = 241;
    const unsigned int num_cols = 886;
    const unsigned int num_elements = num_rows * num_cols;
    const size_t array_sz = num_elements * sizeof(cl_float);
    const std::vector<cl_float> A_1d(num_elements, 1.2345f);
    std::vector<cl_float> B_1d(num_elements, 0);
    const std::vector<std::vector<cl_float> > A_2d(num_rows, std::vector<cl_float>(num_cols, 1.2345f));
    std::vector<std::vector<cl_float> > B_2d(num_rows, std::vector<cl_float>(num_cols, 0));

    // Works as expected
    std::cout << "START 1D TEST\n";
    opencl.test1D(A_1d, B_1d, array_sz);
    std::cout << "1D TEST COMPLETE\n";

    // Crashes
    std::cout << "START 2D TEST\n";
    opencl.test2D(A_2d, B_2d, array_sz);
    std::cout << "2D TEST COMPLETE\n";

    return 0;
}

OpenCl.h

#pragma once
#define __CL_ENABLE_EXCEPTIONS

// Third-party headers
#include <CL/cl.hpp>

class OpenCl {
  public:
    OpenCl();
    void test1D(const std::vector<cl_float> &A,
                std::vector<cl_float> &B,
                const size_t array_sz);
    void test2D(const std::vector<std::vector<cl_float> > &A,
                std::vector<std::vector<cl_float> > &B,
                const size_t array_sz);
  private:
    cl::Context context;
    cl::CommandQueue queue;
};

OpenCl.cpp

// Class header
#include "OpenCl.h"

// System headers
#include <iostream>
#include <vector>

// Third-party headers
#include <CL/cl.hpp>

OpenCl::OpenCl()
{
    // Get available platforms
    std::vector<cl::Platform> platforms;
    cl::Platform::get(&platforms);

    // Select the default platform and create a context using the GPU
    cl_context_properties cps[] = {
        CL_CONTEXT_PLATFORM,
        (cl_context_properties)(platforms[0])(),
        0
    };
    context = cl::Context(CL_DEVICE_TYPE_GPU, cps);

    // Get a list of devices on this platform
    std::vector<cl::Device> devices = context.getInfo<CL_CONTEXT_DEVICES>();

    // Create a command queue and use the first device
    queue = cl::CommandQueue(context, devices[0]);
}

void OpenCl::test1D(const std::vector<cl_float> &A,
                    std::vector<cl_float> &B,
                    const size_t array_sz)
{
    try {
        // Initialize device buffer
        cl::Buffer A_d = cl::Buffer(context, CL_MEM_READ_ONLY, array_sz);

        // Transfer data to device
        queue.enqueueWriteBuffer(A_d, CL_TRUE, 0, array_sz, &A[0]);

        // Transfer data from device
        std::cout << "B[0]: " << B[0] << "\n";
        queue.enqueueReadBuffer(A_d, CL_TRUE, 0, array_sz, &B[0]);
        std::cout << "B[0]: " << B[0] << "\n";
    } catch(cl::Error &error) {
        std::cout << error.what() << "(" << error.err() << ")" << std::endl;
        std::cout << "Program failed!\n";
    }
}

void OpenCl::test2D(const std::vector<std::vector<cl_float> > &A,
                    std::vector<std::vector<cl_float> > &B,
                    const size_t array_sz)
{
    try {
        // Initialize device buffer
        cl::Buffer A_d = cl::Buffer(context, CL_MEM_READ_ONLY, array_sz);

        // Transfer data to device
        queue.enqueueWriteBuffer(A_d, CL_TRUE, 0, array_sz, &A[0][0]);

        // Transfer data from device
        std::cout << "B[0][0]: " << B[0][0] << "\n";
        queue.enqueueReadBuffer(A_d, CL_TRUE, 0, array_sz, &B[0][0]);
        std::cout << "B[0][0]: " << B[0][0] << "\n";
    } catch(cl::Error &error) {
        std::cout << error.what() << "(" << error.err() << ")" << std::endl;
        std::cout << "Program failed!\n";
    }
}

Answer 1

std::vector< std::vector<float> > 持有的内存不是连续的，所以你不能在一次操作中复制它。你必须

size_t row_size = A[0].size() * sizeof(A[0][0]);

for(size_t row = 0; row < A.size(); ++row)
    queue.enqueueWriteBuffer(A_d, CL_TRUE, /*offset=*/row * row_size, /*size=*/row_size, &A[row][0]);

但是，如果您的数据以连续数组的形式放置(如您的 test1D )，您的性能会更好。