Another useless benchmark to illustrate a point

threads.c

// 2017-04-30 jorge@jorgechamorro.com 
// See http://www.eevblog.com/forum/projects/in-search-of-a-supercomputer

#include <pthread.h>
#include <stdlib.h>

#define BUF_SIZE 16*1024*1024
pthread_t t1, t2, t3, t4;

double* nu_buffer () { return (double*) malloc(BUF_SIZE); }

void* thread_proc (void* arg) {
    int i= BUF_SIZE/8;
    double* buffer= nu_buffer();
    while (i--) buffer[i]= (((double*) arg)[i] + buffer[i]) / 2.0;
    return buffer;
}

void do_threads_stuff (double* buffer) {
    pthread_create(&t1, NULL, thread_proc, buffer);
    pthread_create(&t2, NULL, thread_proc, buffer);
    pthread_create(&t3, NULL, thread_proc, buffer);
    pthread_create(&t4, NULL, thread_proc, buffer);
    void* r;
    pthread_join(t1, &r), free(r);
    pthread_join(t2, &r), free(r);
    pthread_join(t3, &r), free(r);
    pthread_join(t4, &r), free(r);
}

int main (void) {
    double* buffer= nu_buffer();
    do_threads_stuff(buffer);
    //free(buffer); return 0;
}

/*
The i7 Mac:
unibodySierra:Desktop admin$ gcc -O0 threads.c -o threads
unibodySierra:Desktop admin$ time ./threads

real	0m0.054s
user	0m0.084s
sys	0m0.073s

And the OPi Zero:
pi@orangepi:~$ gcc -lpthread -O0 threads.c -o threads
pi@orangepi:~$ time ./threads

real	0m0.166s
user	0m0.440s
sys	0m0.140s

And the Mac is 0,166/0,054= only 3x times faster.
*/