Cuda官方案例分析 asyncAPI 两种测试内核函数运行时间的方法（CPU/GPU）

1、使用Cuda提供的Event进行计时

    // create cuda event handles
    cudaEvent_t start, stop;
    checkCudaErrors(cudaEventCreate(&start));
    checkCudaErrors(cudaEventCreate(&stop));
    // record timestamp before and after running of kernel_function
    cudaEventRecord(start, 0);
    cudaMemcpyAsync(d_a, a, nbytes, cudaMemcpyHostToDevice, 0);
    increment_kernel<<<blocks, threads, 0, 0>>>(d_a, value);
    cudaMemcpyAsync(a, d_a, nbytes, cudaMemcpyDeviceToHost, 0);
    cudaEventRecord(stop, 0);
    // get elapsetime through cudaEventElapsedTime, it is calculated by the unit of ms
    checkCudaErrors(cudaEventElapsedTime(&gpu_time, start, stop));
    printf("time spent executing by the GPU: %.2f\n", gpu_time/1000);

2、使用CPU记录内核程序运行时间

    //initialization
    StopWatchInterface *timer = NULL;
    sdkCreateTimer(&timer);
    sdkResetTimer(&timer);
    //get the ti