#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/time.h>
#include <sys/mman.h>

volatile unsigned sink;

double second() {
    struct timeval tv;
    gettimeofday(&tv,0);
    return tv.tv_sec + 1e-6 * tv.tv_usec;
}

int
main(int argc, char *argv[]) {
    int doWrite = 1;
    unsigned size = 80 * 1024 * 1024;

    int letter;
    while ((letter = getopt(argc, argv, "s:wrvh?" )) != -1) {
	switch(letter) {
	case 's': size = atoi(optarg) * 1024 * 1024; break;
	case 'w': doWrite = 1; break;
	default:
	    fprintf(stderr,"useup [-s mb][-w]\n");
	    exit(1);
	}
    }
    int *base = (int*) mmap(0, size, 
			      PROT_READ|PROT_WRITE, 
			      MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
    if (base == MAP_FAILED) {
	perror("mmap failed");
	exit(1);
    }

    int *end = base + size/4;

    while (1) {
	double start = second();
	if (doWrite)
	    for (int *p = base; p < end; p += 1024)
		*p = 0;
	else {
	    unsigned sum = 0;
	    for (int *p = base; p < end; p += 1024)
		sum += *p;
	    sink = sum;
	}
	printf("%f\n",1000*(second() - start));
    }
}