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为了测试GPU函数的耗时，可以使用 CUDA 提供的计时功能：cudaEventCreate, cudaEventRecord, 和 cudaEventElapsedTime。这些函数可以帮助你测量某个 CUDA 操作（如设置设备）所花费的时间。

一、记录耗时案例

以下是一个示例程序，它测量调用 cudaSetDevice 所花费的时间：

#include <iostream>
#include <vector>
#include <cuda_runtime.h>__global__ void dummyKernel() {// Dummy kernel to ensure CUDA context is initialized
}int main() {// CUDA device IDsint device1 = 0;int numIterations = 10; // Number of times to call cudaSetDevice// Create CUDA eventscudaEvent_t start, stop;cudaEventCreate(&start);cudaEventCreate(&stop);// Vector to store elapsed timesstd::vector<float> elapsedTimes(numIterations);// Set initial device (optional, but ensures a known starting state)cudaSetDevice(device1);// Measure time for multiple cudaSetDevice callsfor (int i = 0; i < numIterations; ++i) {// Record the start eventcudaEventRecord(start, 0);// Set the device (this is the operation we are timing)cudaSetDevice(device1);// Record the stop eventcudaEventRecord(stop, 0);// Measure the elapsed time between the start and stop eventscudaEventElapsedTime(&elapsedTimes[i], start, stop);// Output resultsstd::cout << "Number of iterations: i " << i << std::endl;std::cout << " time to set device " << device1 << ": " << elapsedTimes[i] << " ms" << std::endl;}// Calculate statistics (e.g., average time)float totalTime = 0.0f;for (float time : elapsedTimes) {totalTime += time;}float averageTime = totalTime / numIterations;// Output resultsstd::cout << "Number of iterations: " << numIterations << std::endl;std::cout << "Average time to set device " << device1 << ": " << averageTime << " ms" << std::endl;// Optionally, run a dummy kernel to ensure CUDA is initialized and readydummyKernel<<<1, 1>>>();cudaDeviceSynchronize();// Clean upcudaEventDestroy(start);cudaEventDestroy(stop);return 0;
}

二、编译和运行

         2.1 编译: 使用 nvcc 编译这个 CUDA 程序。（上面程序文件铭为test_cudaSetDevice_multiple.cu）

nvcc -o test_cudaSetDevice_multiple test_cudaSetDevice_multiple.cu

        2.2 运行: ，然后运行生成的可执行文件。

./test_cudaSetDevice_multiple

哈哈哈，就得到运行结果啦！