我对嵌入式和 OpenCL 很陌生，我目前正在尝试开发一个示例代码来执行到支持 OpenCL 1.1 EP 的 i.MX6q 板。
我必须从头开始，所以我按照这些教程、OpenCL 1.1 参考页面以及这个 OpenCL 示例来制作我的第一个 OpenCL 实现/应用程序。
基本上我想做的是开发一个“性能测试”在板上运行。它包含两个 int 数组（输入和输出），用随机值填充第一个数组，然后使用 OpenCL 工作项将其粘贴到输出数组中。
我对 clEnqueue(Read/Write)Buffer 函数和 clCreateBuffer 标志（尤其是 CL_MEM_USE_HOST_PTR）感到很困惑，所以我决定看看并练习一下。
我的代码可以正确编译并正确运行，但是当我读取输出数组值时，它们仍然保持为 0。
这是我的代码（C++）：
void buffer_copy(char* kernelfile)
{
cl_platform_id platform_id;
cl_device_id device_id;
cl_context context;
cl_command_queue cmd_queue;
cl_program program;
// Retrieving all the OpenCL data needed
// to start the performance test
platform_id = get_platform();
device_id = get_device(platform_id);
context = get_context(platform_id, device_id);
cmd_queue = get_command_queue(context, device_id);
program = get_program(context, kernelfile);
cl_mem buffer_input, buffer_output;
size_t buffer_width = 640, buffer_height = 480;
size_t buffer_size = buffer_width * buffer_height;
cl_kernel kernel;
cl_int err = 0;
char* options = "-Werror -cl-std=CL1.1";
int data_input[buffer_size];
int data_output[buffer_size];
// Assigning random values in the data_input array and
// initializing the data_output array to zero-values
srand(time(NULL));
for (size_t index = 0; index < buffer_size; ++index)
{
data_input[index] = rand();
data_output[index] = 0;
}
// Creating OpenCL buffers
buffer_input = clCreateBuffer(context, CL_MEM_READ_ONLY | CL_MEM_USE_HOST_PTR, buffer_size * sizeof(int), data_input, &err);
assert(err == CL_SUCCESS);
buffer_output = clCreateBuffer(context, CL_MEM_WRITE_ONLY | CL_MEM_USE_HOST_PTR, buffer_size * sizeof(int), data_output, &err);
assert(err == CL_SUCCESS);
err = clBuildProgram(program, 1, &device_id, options, NULL, NULL);
assert(err == CL_SUCCESS);
kernel = clCreateKernel(program, "buffer_copy", &err);
assert(err == CL_SUCCESS);
clSetKernelArg(kernel, 0, sizeof(cl_mem), &buffer_input);
clSetKernelArg(kernel, 1, sizeof(cl_mem), &buffer_output);
size_t device_max_work_group_size;
size_t global_work_size, local_work_size;
size_t preferred_work_group_size_multiple;
cl_ulong global_mem_size, max_mem_alloc_size;
clGetDeviceInfo(device_id, CL_DEVICE_GLOBAL_MEM_SIZE, sizeof(cl_ulong), &global_mem_size, NULL);
clGetDeviceInfo(device_id, CL_DEVICE_MAX_MEM_ALLOC_SIZE, sizeof(cl_ulong), &max_mem_alloc_size, NULL);
clGetDeviceInfo(device_id, CL_DEVICE_MAX_WORK_GROUP_SIZE, sizeof(size_t), &device_max_work_group_size, NULL);
std::cout << "Global device memory size: " << global_mem_size << " bytes" << std::endl;
std::cout << "Device max memory allocation size: " << max_mem_alloc_size << " bytes" << std::endl;
std::cout << "Device max work group size: " << device_max_work_group_size << std::endl;
clGetKernelWorkGroupInfo(kernel, device_id, CL_KERNEL_WORK_GROUP_SIZE, sizeof(size_t), &global_work_size, NULL);
std::cout << "global_work_size value: " << global_work_size << std::endl;
clGetKernelWorkGroupInfo(kernel, device_id, CL_KERNEL_PREFERRED_WORK_GROUP_SIZE_MULTIPLE, sizeof(size_t), &preferred_work_group_size_multiple, NULL);
local_work_size = global_work_size / preferred_work_group_size_multiple;
std::cout << "local_work_size value: " << local_work_size << std::endl;
cl_event events[2];
err = clEnqueueNDRangeKernel(cmd_queue, kernel, 1, NULL, &global_work_size, &local_work_size, 0, 0, &events[0]);
assert (err == CL_SUCCESS);
err = clEnqueueReadBuffer(cmd_queue, buffer_output, CL_TRUE, 0, buffer_size * sizeof(int), data_output, 0, NULL, &events[1]);
assert (err == CL_SUCCESS);
err = clWaitForEvents(2, events);
assert (err == CL_SUCCESS);
for (size_t index = 0; index < buffer_size; ++index)
{
if (data_input[index] != data_output[index])
{
std::cerr << "Error, values differ (at index " << index << ")." << std::endl;
break;
}
else
{
//std::cout << "data_input[index] =\t" << data_input[index] << std::endl;
//std::cout << "data_output[index] =\t" << data_output[index] << std::endl;
}
}
cl_ulong time_start, time_end;
double total_time;
clGetEventProfilingInfo(events[0], CL_PROFILING_COMMAND_START, sizeof(time_start), &time_start, NULL);
clGetEventProfilingInfo(events[1], CL_PROFILING_COMMAND_END, sizeof(time_end), &time_end, NULL);
total_time = time_end - time_start;
std::cout << "Execution time in milliseconds: " << (total_time / 1000000.0) << " ms" << std::endl;
clReleaseKernel(kernel);
clReleaseProgram(program);
clReleaseMemObject(buffer_input);
clReleaseMemObject(buffer_output);
clReleaseCommandQueue(cmd_queue);
clReleaseContext(context);
}
这是我的 OpenCL 内核：
__kernel void buffer_copy(__global int* input, __global int* output)
{
int id = get_global_id(0);
output[id] = input[id];
}
现在我只是想让它工作，而不是优化它。而且我认为我在这里和那里都错过了好点，但我无法抓住它们。在我看来，我混淆了 clCreateBuffer 标志。
你们能启发我并帮助我解决这个问题吗？
编辑：更新代码+新信息！
似乎值粘贴得很好，但仅根据内核工作组大小：CL_DEVICE_MAX_WORK_GROUP_SIZE 返回 1024，CL_KERNEL_WORK_GROUP_SIZE 也返回 1024（这也很奇怪）。所以我的数组的前 1024 个整数被很好地复制/粘贴，但之后它就不再工作了。为了验证这一点，我将 global_work_group_size 手动设置为 32，再次运行我的程序，然后正确粘贴唯一的前 32 个整数。我真的不明白这里发生了什么。