操作系统导论-课后作业-ch19-2.

代码如下：

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

#define PGSIZE 4096

//return us
int time_diff(struct timeval* t1, struct timeval* t2) {
    return (t2->tv_sec - t1->tv_sec) * 1000000 + (t2->tv_usec - t1->tv_usec);
}

int main(int argc, char* argv[]) {
    if (argc != 3) {
        fprintf(stderr, "too many or too few arguments\n");
        exit(1);
    }
    int i;
    int pageCount = atoi(argv[1]);
    int num = atoi(argv[2]);
    struct timeval curr, now;
    int size = (pageCount * PGSIZE) / sizeof(int);
    int arr[size];
    if (gettimeofday(&curr, NULL) == -1) {
        fprintf(stderr, "gettimeofday error\n");
        exit(1);
    }
    for (i = 0; i < num; ++i) {
        arr[(rand() % pageCount) * (PGSIZE / sizeof(int))] = i;
    }
    if (gettimeofday(&now, NULL) != 0) {
        fprintf(stderr, "gettimeofday error\n");
        exit(1);
    }
    printf("time elaps %d us\n", time_diff(&curr, &now));
    return 0;
}

运行结果如下：

100000次访问消耗1230us，平均每次访问时间为12.3ns