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  • OpenMP性能优化方案

    #include <iostream>
    #include <windows.h>
    using namespace std;

    struct Count
    {
        long count1;
        char space[64];  // 此处增加64字节的“无用”空间,目的就是使得count1和count2位于不同的Cache行,从而避免Cache行同步引起的“乒乓效应”,可以尝试去掉这64字节的“无用”空间,将会得到令人诧异的运行结果,要探明深层原因,可以搜索一下“乒乓效应 CPU cache”

        long count2;
    };
    DWORD WINAPI Calculate1(void *p)
    {
        double x = 0,y = 0;
        long* c1 = (long*)p;
        for(; x <= 0.5;x += 0.0001) 
            for(y = 0;y <= 1;y += 0.0001) 
            { 
                if (x*x + y*y <= 1) (*c1)++; 
            } 
        return 0;
    }
    DWORD WINAPI Calculate2(void *p)
    {
        double i = 0,j = 0;//16
        long* c2 = (long*)p;
        for(i=0.5001;i <=1;i+=0.0001) 
            for(j=0;j <=1;j+=0.0001) 
            { 
                if(i*i+j*j <=1) (*c2)++; 
            } 
        return 0;
    }

    int main()
    {
        DWORD pThreadID;
        Count cnt;

        DWORD startTime = 0,endTime = 0;
        startTime= GetTickCount(); 
        Calculate1(&cnt.count1);
        Calculate2(&cnt.count2);
        cout << "Serial calculate cost " << GetTickCount() - startTime << "ms." << endl;

        cnt.count1 = 0;
        cnt.count2 = 0;
        startTime= GetTickCount();

        HANDLE hThread1 = CreateThread (NULL,
                                        0,
                                        Calculate1,
                                        &cnt.count1,
                                        0,
                                        &pThreadID);

        HANDLE hThread2 = CreateThread (NULL,
                                        0,
                                        Calculate2,
                                        &cnt.count2,
                                        0,
                                        &pThreadID);


        WaitForSingleObject(hThread1, INFINITE); 
        WaitForSingleObject(hThread2, INFINITE); 
        endTime=GetTickCount();

        cout << "Parallel calculate cost " << endTime-startTime << "ms." << endl; 
    }

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  • 原文地址:https://www.cnblogs.com/jast/p/4516471.html
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