Question

我正在尝试学习OpenCL，但我甚至无法使一个简单的内核工作。

下面的代码来自书＆＃34; OpenCL Programming by Example＆＃34;，我对其进行了修改，修改，修改......但仍然没有找到解决问题的方法。

每次我在我的PC（带有Radeon R3的AMD Athlon 5350 APU）中执行程序时，它会将结果打印为＆＃34; 0.0000＆＃34;。如果我运行相同的可执行文件，在我的另一台机器（这是HD的克隆，所以一切都是相同的）与NVIDIA 1080 TI，程序输出＆＃34; 3.000＆＃34;结果。

我注意到编译器输出中有一个警告，因此我将过时的clCreateCommandQueue调用更改为clCreateCommandQueueWithProperties（）。

现在......它只是段错误（使用printf（）测试我知道clCreateCommandQueueWithProperties期间/之后的段错误。）

在配备NVIDIA GPU的系统上，它可以正常工作。

我错过了什么？

#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <time.h>
#include <malloc.h>

#include <CL/cl.h>

#define VECTOR_NS 4096
#define VECTOR_SIZE (VECTOR_NS*sizeof(float))

static const char* saxpy_kernel =
    "__kernel void saxpy_kernel(__global float *A, __global float *B, __global float *C)\n"
    "{\n"
        "int index = get_global_id(0);\n"
        "C[0] = 3;\n"
    "}\n"
    ;

int main(void)
{
    int i;
    float total;
    float* A;
    float* B;
    float* C;
    float* Cmapped;
    cl_mem Acl;
    cl_mem Bcl;
    cl_mem Ccl;
    cl_context context;
    cl_platform_id* platforms;
    cl_uint num_platforms;
    cl_uint num_devices;
    cl_command_queue queue;
    cl_kernel kernel;
    cl_int clStatus;

    // Get platform and device information
    platforms = NULL;
    //Set up the Platform
    clStatus = clGetPlatformIDs(0, NULL, &num_platforms);
    platforms = (cl_platform_id *)malloc(sizeof(cl_platform_id)*num_platforms);
    clStatus = clGetPlatformIDs(num_platforms, platforms, NULL);
    //Get the devices list and choose the device you want to run on
    cl_device_id* device_list = NULL;

    clStatus = clGetDeviceIDs( platforms[0], CL_DEVICE_TYPE_GPU, 0, NULL, &num_devices);
    device_list = (cl_device_id *) malloc(sizeof(cl_device_id)*num_devices);

    clStatus = clGetDeviceIDs( platforms[0], CL_DEVICE_TYPE_GPU, num_devices, device_list, NULL);
    // Create one OpenCL context for each device in the platform
    context = clCreateContext( NULL, num_devices, device_list, NULL, NULL, &clStatus);

    /* Create the command queue */
    //queue = clCreateCommandQueue(context, device_list[0], 0, &clStatus);
    queue = clCreateCommandQueueWithProperties(context, device_list[0], NULL, &clStatus);

    if(clStatus != CL_SUCCESS){
        fprintf(stderr, "ERROR: failed to execute the kernel: %d.\n", clStatus);
        exit(1);
    }

    /* */
    if((A = aligned_alloc(sysconf(_SC_PAGESIZE), VECTOR_SIZE)) == NULL){
        fprintf(stderr, "ERROR: failed to allocate memory.\n");
        exit(1);
    }
    if((B = aligned_alloc(sysconf(_SC_PAGESIZE), VECTOR_SIZE)) == NULL){
        fprintf(stderr, "ERROR: failed to allocate memory.\n");
        exit(1);
    }
    if((C = aligned_alloc(sysconf(_SC_PAGESIZE), VECTOR_SIZE)) == NULL){
        fprintf(stderr, "ERROR: failed to allocate memory.\n");
        exit(1);
    }

    /* Initialize it */
    i = 0;
    do {
        A[i] = 1;
        B[i] = 2;
        C[i] = 0;
    } while(++i != VECTOR_NS);

    Acl = clCreateBuffer(context, CL_MEM_USE_HOST_PTR | CL_MEM_READ_WRITE, VECTOR_SIZE, A, &clStatus); // CL_MEM_READ_ONLY
    Bcl = clCreateBuffer(context, CL_MEM_USE_HOST_PTR | CL_MEM_READ_WRITE, VECTOR_SIZE, B, &clStatus); // CL_MEM_READ_ONLY
    Ccl = clCreateBuffer(context, CL_MEM_USE_HOST_PTR | CL_MEM_READ_WRITE, VECTOR_SIZE, C, &clStatus); // CL_MEM_WRITE_ONLY

    // Create a program from the kernel source
    // Build the program
    cl_program program = clCreateProgramWithSource(context, 1, (const char**)&saxpy_kernel, NULL, &clStatus);

    if(clStatus != CL_SUCCESS){
        fprintf(stderr, "ERROR: failed to compile the OpenCL code.\n");
        exit(1);
    }

    clStatus = clBuildProgram(program, 1, device_list, NULL, NULL, NULL);

    if(clStatus != CL_SUCCESS){
        fprintf(stderr, "ERROR: failed to compile the OpenCL code.\n");
        exit(1);
    }

    // Create the OpenCL kernel
    kernel = clCreateKernel(program, "saxpy_kernel", &clStatus);
    // Set the arguments of the kernel
    clSetKernelArg(kernel, 0, sizeof(cl_mem), (void*)&Acl);
    clSetKernelArg(kernel, 1, sizeof(cl_mem), (void*)&Bcl);
    clSetKernelArg(kernel, 2, sizeof(cl_mem), (void*)&Ccl);

    // Execute the OpenCL kernel on the list
    size_t global_size = VECTOR_NS; // Process the entire lists
    size_t local_size = 1;

    // Process one item at a time
    clStatus = clEnqueueNDRangeKernel(queue, kernel, 1, NULL, &global_size, &local_size, 0, NULL, NULL);

    if(clStatus != CL_SUCCESS){
        fprintf(stderr, "ERROR: failed to execute the kernel: %d.\n", clStatus);
        exit(1);
    }

    //* Clean up and wait for all the comands to complete. */
    clFlush(queue);

    /* Display the result to the screen */
    Cmapped = (float*) clEnqueueMapBuffer(queue, Ccl, CL_TRUE, CL_MAP_READ, 0, VECTOR_SIZE, 0, NULL, NULL, &clStatus); // CL_MEM_USE_HOST_PTR

    if(clStatus != CL_SUCCESS){
        fprintf(stderr, "ERROR: failed to execute the kernel: %d.\n", clStatus);
        exit(1);
    }

    total = 0;
    for(i = 0; i < VECTOR_NS; i++)
        total += C[i];

    printf("TOTAL: %f\n", total);

    /* Clean up and wait for all the comands to complete. */
    clFlush(queue);
    clFinish(queue);

    /* Finally release all OpenCL allocated objects and host buffers. */
    clReleaseKernel(kernel);
    clReleaseProgram(program);
    clReleaseMemObject(Acl);
    clReleaseMemObject(Bcl);
    clReleaseMemObject(Ccl);
    clReleaseCommandQueue(queue);
    clReleaseContext(context);

    free(platforms);
    free(device_list);

    return 0;
}

Answer 1

虽然您的代码在我的计算机上按原样运行，但我认为这可能会导致您的问题。电话

Cmapped = (float*)clEnqueueMapBuffer(queue, Ccl, CL_TRUE, CL_MAP_READ, 0, VECTOR_SIZE, 0, NULL, NULL, &clStatus);

更改Cmapped，但您尝试从

中的原始C缓冲区中读取

total = 0;
for(i = 0; i < VECTOR_NS; i++)
    total += C[i];

这应该是

total = 0;
for(i = 0; i < VECTOR_NS; i++)
    total += Cmapped[i];

但是，由于您使用CL_MEM_USE_HOST_PTR标志创建了缓冲区，因此如果使用clEnqueueReadBuffer，则使用原始指针作为目标，OpenCL驱动程序也应该能够优化复制操作：

clEnqueueReadBuffer(queue, Ccl, CL_TRUE, 0, VECTOR_SIZE, C, 0, NULL, NULL);

如果OpenCL实现没有将数据缓存到设备内存，那么这应该是无操作。

如何创建OpenCL命令队列？

1 个答案: