False sharing

#include <iostream>
#include <ctime>
#include <omp.h>

using std::cout;
using std::endl;

const double M=8e8;

//single thread work to do
void one_thread() 
{
    long int n1=1, n2=1;
    for(; n1<M; n1+=n1%3);
    for(; n2<M; n2+=n2%3);
    cout << "Sum = " << n1 + n2 << endl;
}

//multi thread work to do
void multi_thread() 
{
    struct T
    {
        long int n1;
        char chuck[64];//should be commented to see false sharing effect
        long int n2;
    } t;
    t.n1 = 1;
    t.n2 = 1;
    #pragma omp parallel num_threads(2) shared(M,t)
    {
        #pragma omp sections
        {
            #pragma omp section
            for(; t.n1<M; t.n1+=t.n1%3);

            #pragma omp section
            for(; t.n2<M; t.n2+=t.n2%3);
        }
    }
    cout << "Sum = " << t.n1 + t.n2 << endl;
}

time_t start, end;
double diff;

int main(int argc, char* argv[]) 
{
    time(&start);
    multi_thread();
    time(&end);
    diff=difftime(end, start);
    cout<<diff<<" seconds elapsed for multi thread calculation."<<endl;

    time(&start);
    one_thread();
    time(&end);
    diff=difftime(end, start);
    cout<<diff<<" seconds elapsed for 1 thread calculation."<<endl;
    return 0;
}