cache_line.c

#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <pthread.h>

#define GET_US(X) (X.tv_sec * 1000000 + X.tv_usec)
#define ITE 5000
#define MAX 3000000
#define SIZE 9

long int exe_time[2][SIZE] = {};
int var_array1024[SIZE][1024] __attribute__ ((aligned(1024)));

int get_time(int [][1024]);
void main_pthread(int *, int *);
void *counting_thread(void *);

int main() {
    get_time(var_array1024);

    int i = 1, j = 0, max_diff = 0;
    for (i = 0; i < SIZE-1; i++) {
        int diff = abs(exe_time[1][i] - exe_time[1][i+1]);
        if (diff > max_diff) {
            max_diff = diff;
            j = i;
        }
    }

    printf("\nL1d cache line size = %ld bytes\n", exe_time[0][++j]);

    return 0;
}

int get_time(int arr[][1024]) {
    struct timeval start, end;
    struct timezone z;
    long int total;
    int a = 1, i = 0, j, k;

    for (k = 0; k < SIZE-1; k++) {
        for (total = 0, j = 0; j < ITE; j++) {
            if (gettimeofday(&start, &z)) goto error_exit;
            main_pthread(&arr[k][0], &arr[k][a]);       // make sure it exits only after completing
            if (gettimeofday(&end, &z)) goto error_exit;
            total += GET_US(end) - GET_US(start);
        }
        exe_time[0][k] = a * 4;
        exe_time[1][k] = total / ITE;
        printf("%ld\t- (%p and %p)\tdiff = %ld\tAvg=%ld\n", exe_time[0][k],
               &arr[k][0], &arr[k][a], (uintptr_t) &arr[k][a] - (uintptr_t) &arr[k][0], exe_time[1][k]);
        a = a * 2;
    }

    for (total = 0, j = 0; j < ITE; j++) {
        if (gettimeofday(&start, &z)) goto error_exit;
        main_pthread(NULL, NULL);                       // make sure it exits only after completing
        if (gettimeofday(&end, &z)) goto error_exit;
        total += GET_US(end) - GET_US(start);
    }
    exe_time[0][SIZE-1] = 0;
    exe_time[1][SIZE-1] = total / ITE;
    printf("%s\t- (%d and %d)\t\t\t\t\t\t\t\tdiff = %d\tAvg=%ld\n", "NULL", 0, 0, 0, exe_time[1][SIZE-1]);

    return 0;

    error_exit:
    printf("Cannot read time, too bad\n");
    return -1;
}

void main_pthread(int *c1, int *c2) {
    pthread_t tid1, tid2;
    pthread_attr_t attr;

    pthread_attr_init(&attr); // set default attributes
    pthread_create(&tid1, &attr, counting_thread, c1); // create new thread
    pthread_create(&tid2, &attr, counting_thread, c2); // create new thread

    void *p;
    pthread_join(tid1, &p);
    pthread_join(tid2, &p);

    return;
}

void *counting_thread(void *arg) {
    int local, *j;

    if (arg) { j = arg; }
    else { j = &local; }

    for (*j = 0; *j < MAX; (*j)++);

    pthread_exit(NULL);
}