CUDA并行计算基础代码-第二版

经过大牛指导，把多个线程装入一个线程块中。计算速度大幅提高！

第一版代码每个线程块仅包含一个线程，第二版一个线程块包含501个线程。

第一版GPU计算速度和CPU差不多，改进之后GPU运行速度达到了CPU的50倍！

#include<cuda_runtime.h>
#include<windows.h>
#include<iostream>
using namespace std;
const int nMax = 30000;
__global__ void addKernel(float *aaa,float *bbb, float *ccc)
{
	//int i = blockIdx.x;
	int i = threadIdx.x + blockIdx.x*blockDim.x;
	ccc[i] = 0;
	if (i < nMax)for (int j = 0; j < 500; j++)ccc[i] += aaa[i] * bbb[i];
}
void add(float *a, float *b,float *c,int i){
	for (int j = 0; j<500; j++) c[i] += a[i] * b[i];
}
int main(){
	float a[nMax], b[nMax], c[nMax];
	float *devA, *devB, *devC;
	clock_t startT, endT;
	for (int i = 0; i < nMax; i++){
		a[i] = i*1.010923;
		b[i] = 2.13*i;
	}
	startT = clock();
	cudaMalloc((void**)&devA, nMax*sizeof(float));
	cudaMalloc((void**)&devB, nMax*sizeof(float));
	cudaMalloc((void**)&devC, nMax*sizeof(float));
	endT = clock();
	cout << "分配设备空间耗时 " << endT - startT << "ms"<<endl;


	startT = clock();
	cudaMemcpy(devA, a,nMax*sizeof(float),cudaMemcpyHostToDevice);
	cudaMemcpy(devB, b, nMax*sizeof(float), cudaMemcpyHostToDevice);
	endT = clock();
	cout << "数据从主机写入设备耗时 " << endT - startT << "ms" << endl;

	startT = clock();

	cudaEvent_t start1;
	cudaEventCreate(&start1);
	cudaEvent_t stop1;
	cudaEventCreate(&stop1);
	cudaEventRecord(start1, NULL);

	addKernel<<<60,501>>>(devA, devB, devC);

	cudaEventRecord(stop1, NULL);
	cudaEventSynchronize(stop1);
	float msecTotal1 = 0.0f;
	cudaEventElapsedTime(&msecTotal1, start1, stop1);
	//cout << msecTotal1 << "ddd" << endl;
	endT = clock();
	cout << "GPU计算耗时 " << msecTotal1 << "ms" << endl;

	startT = clock();
	cudaMemcpy(c, devC, nMax*sizeof(float), cudaMemcpyDeviceToHost);
	endT = clock();
	cout << "数据从设备写入主机耗时 " << endT - startT << "ms" << endl;

	cout <<"GPU计算结果 "<< c[nMax - 1] << endl;
	for (int i = 0; i < nMax; i++){
		a[i] = i*1.010923;
		b[i] = 2.13*i;
		c[i] = 0;
	}
	startT = clock();
	for (int i = 0; i < nMax; i++){
		add(a, b, c, i);
	}
	endT = clock();
	cout << "CPU计算耗时 " << endT - startT << "ms" << endl;
	cout << "CPU计算结果 " << c[nMax - 1] << endl;
	cin >> a[0];
	return 0;
}