Illustrate processor cache effects

gistfile1.cpp

#include <iostream>
#include <sys/time.h>
using namespace std;

//http://igoro.com/archive/gallery-of-processor-cache-effects/

int print_interval(timeval t1, timeval t2){
    double elapsed;
    elapsed = (t2.tv_sec - t1.tv_sec) * 1000.0;      // sec to ms
    elapsed += (t2.tv_usec - t1.tv_usec) / 1000.0;   // us to ms
    cout<<elapsed<<"\t";
}

int steps = 64*1024*1024;
int update_every_kth(int size, int k){
    timeval t1, t2;
    double elapsed;
    gettimeofday(&t1, NULL);

    int* arr = new int[size];
    int size_mod = size-1;
    for(int i=0; i<steps; i++){
        arr[(i*16)&size_mod]++;
    }

    gettimeofday(&t2, NULL);
    cout<<k<<":";
    print_interval(t1,t2);

    delete arr;
    return 0;
}

//For hardware complexity
static int a,b,c,d,e,f,g;
static int wired(){
    a=b=c=d=e=f=g=0;
    timeval t1, t2, t3, t4;
    gettimeofday(&t1, NULL);
    for(int i=0; i<400000000; i++) {
        a++,b++,c++,d++;
        //a++,c++,e++,g++;
    }

    gettimeofday(&t2, NULL);
    for(int i=0; i<400000000; i++) {
        //a++,b++,c++,d++;
        a++,c++,e++,g++;
    }

    gettimeofday(&t3, NULL);
    for(int i=0; i<400000000; i++) {
        a++,c++;
    }
    gettimeofday(&t4, NULL);

    cout<<"1: ";
    print_interval(t1,t2);

    cout<<"2: ";
    print_interval(t2,t3);

    cout<<"3: ";
    print_interval(t3,t4);

    cout<<"\n";
//    cout <<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<"\n";
    return 0;
}

int main()
{
    for(int i=0; i<20; i++){
        wired();
    }
    int max_size = 64*1024*1024;
    for(int j=1024; j<=max_size; j*=2){
        cout << j <<"\t";
        for(int i=1; i<257; i*=2){
                update_every_kth(j, i);
        }
        cout<<"\n";
    }
    return 0;
}