CUDA：cudaMemcpy 仅在仿真模式下工作

Question

我刚刚开始学习如何使用 CUDA。我正在尝试运行一些简单的示例代码：

float *ah, *bh, *ad, *bd;
ah = (float *)malloc(sizeof(float)*4);
bh = (float *)malloc(sizeof(float)*4);
cudaMalloc((void **) &ad, sizeof(float)*4);
cudaMalloc((void **) &bd, sizeof(float)*4);
... initialize ah ...

/* copy array on device */
cudaMemcpy(ad,ah,sizeof(float)*N,cudaMemcpyHostToDevice);
cudaMemcpy(bd,ad,sizeof(float)*N,cudaMemcpyDeviceToDevice);
cudaMemcpy(bh,bd,sizeof(float)*N,cudaMemcpyDeviceToHost);

当我在仿真模式（nvcc -deviceemu）下运行时，它运行良好（并且实际上复制了数组）。 但是当我以常规模式运行它时，它运行时没有错误，但从不复制数据。就好像 cudaMemcpy 行被忽略了。

我做错了什么？

非常感谢， 贾森

Answer 1

您应该检查错误，最好是在每个 malloc 和 memcpy 上检查错误，但只需在最后执行一次就足够了 (cudaGetErrorString(cudaGetLastError())。

只是为了检查明显的情况：

• 您确实拥有 CUDA 功能GPU，对吗？运行 deviceQuery SDK 示例来检查设备是否正常工作，并且所有驱动程序均已安装并正常工作。
• N（在 memcpy 中）等于 4（在 malloc 中），对吧？

Answer 2

查看您是否有支持 CUDA 的设备。也许您可以尝试运行下面的代码，看看您得到什么信息：

#include <cstdio>

int main( void ) {
    cudaDeviceProp  prop;

    int count;
    cudaGetDeviceCount( &count );
    for (int i=0; i< count; i++) {
        cudaGetDeviceProperties( &prop, i );
        printf( "   --- General Information for device %d ---\n", i );
        printf( "Name:  %s\n", prop.name );
        printf( "Compute capability:  %d.%d\n", prop.major, prop.minor );
        printf( "Clock rate:  %d\n", prop.clockRate );
        printf( "Device copy overlap:  " );
        if (prop.deviceOverlap)
            printf( "Enabled\n" );
        else
            printf( "Disabled\n");
        printf( "Kernel execution timeout :  " );
        if (prop.kernelExecTimeoutEnabled)
            printf( "Enabled\n" );
        else
            printf( "Disabled\n" );

        printf( "   --- Memory Information for device %d ---\n", i );
        printf( "Total global mem:  %ld\n", prop.totalGlobalMem );
        printf( "Total constant Mem:  %ld\n", prop.totalConstMem );
        printf( "Max mem pitch:  %ld\n", prop.memPitch );
        printf( "Texture Alignment:  %ld\n", prop.textureAlignment );

        printf( "   --- MP Information for device %d ---\n", i );
        printf( "Multiprocessor count:  %d\n",
                    prop.multiProcessorCount );
        printf( "Shared mem per mp:  %ld\n", prop.sharedMemPerBlock );
        printf( "Registers per mp:  %d\n", prop.regsPerBlock );
        printf( "Threads in warp:  %d\n", prop.warpSize );
        printf( "Max threads per block:  %d\n",
                    prop.maxThreadsPerBlock );
        printf( "Max thread dimensions:  (%d, %d, %d)\n",
                    prop.maxThreadsDim[0], prop.maxThreadsDim[1],
                    prop.maxThreadsDim[2] );
        printf( "Max grid dimensions:  (%d, %d, %d)\n",
                    prop.maxGridSize[0], prop.maxGridSize[1],
                    prop.maxGridSize[2] );
        printf( "\n" );
    }
}