cuda编程---cuda的速度计量

版权声明：本文为博主原创文章，转载请加入原文链接，谢谢。。 https://blog.csdn.net/shawncheer/article/details/77931172

一、简述：

1、本文参考 nvidia official tutorial

2、本文重点在于测量带宽的问题。

3、使用 cudaEventCreate() 可以不用与cpu进行同时。减少拥塞。

二、代码：

#include <iostream>
#include <math.h>
#include <stdio.h>

__global__
void saxpy(int n,float a,float *x,float *y)
{
    int i = blockIdx.x*blockDim.x +threadIdx.x;
    if (i < n) y[i] = a*x[i] + y[i];
}

int main(void){
    int N = 1 << 20; //1M element.

    //float *x=new float[N];
    //float *y=new float[N];

    //Allocate Unified Memory -- accessible from CPU or GPU
    float *x, *y, *d_x, *d_y;

    x = (float*)malloc(N*sizeof(float));
    y = (float*)malloc(N*sizeof(float));

    cudaMalloc(&d_x, N*sizeof(float));
    cudaMalloc(&d_y, N*sizeof(float));

    //initialize x and y arrays on the host.
    for (int i=0;i<N;i++){
        x[i]=1.0f;
        y[i]=2.0f;
    }
    cudaEvent_t start, stop;
    cudaEventCreate(&start);
    cudaEventCreate(&stop);

    cudaMemcpy(d_x, x, N*sizeof(float), cudaMemcpyHostToDevice);
    cudaMemcpy(d_y, y, N*sizeof(float), cudaMemcpyHostToDevice);

    cudaEventRecord(start);
    saxpy<<< (N+255)/256, 256>>>(N, 2.0, d_x, d_y);
    cudaEventRecord(stop);

    cudaMemcpy(y, d_y, N*sizeof(float), cudaMemcpyDeviceToHost);

    cudaEventSynchronize(stop);
    float milliseconds = 0;
    cudaEventElapsedTime(&milliseconds, start, stop);

    // Check for errors (all values should be 3.0f)
    float maxError=0.0f;

    for (int i=0;i<N;i++)
        maxError=max(maxError,fabs(y[i]-4.0f));

    printf("Max error: %f . \n", maxError);
    printf("Effective Bandwidth (GB/s): %f .\n", N*4*3/milliseconds/1e6);

    cudaFree(x);
    cudaFree(y);
    cudaFree(d_x);
    cudaFree(d_y);

    cudaEventDestroy(start);
    cudaEventDestroy(stop);

    return 0;
}