Linux timerfd,每隔x秒调用一次函数,不会阻塞代码执行

#include <sys/timerfd.h>
   #include <time.h>
   #include <unistd.h>
   #include <stdlib.h>
   #include <stdio.h>
   #include <stdint.h>        /* Definition of uint64_t */

   #define handle_error(msg) 
           do { perror(msg); exit(EXIT_FAILURE); } while (0)

   int
   main(int argc,char *argv[])
   {
       struct itimerspec new_value;
       int max_exp,fd;
       struct timespec now;
       uint64_t exp,tot_exp;
       ssize_t s;

       if (clock_gettime(CLOCK_REALTIME,&now) == -1)
           handle_error("clock_gettime");

       /* Create a CLOCK_REALTIME absolute timer with initial
          expiration and interval as specified in command line */

       new_value.it_value.tv_sec = now.tv_sec + 1; 
       new_value.it_value.tv_nsec = now.tv_nsec;

       new_value.it_interval.tv_sec = 5;
       new_value.it_interval.tv_nsec = 0;
       max_exp = 5; //say 5 times

       fd = timerfd_create(CLOCK_REALTIME,0);
       if (fd == -1)
           handle_error("timerfd_create");

       if (timerfd_settime(fd,TFD_TIMER_ABSTIME,&new_value,NULL) == -1)
           handle_error("timerfd_settime");

       printf("timer startedn");
       for (tot_exp = 0; tot_exp < max_exp;) {
           s = read(fd,&exp,sizeof(uint64_t));
           if (s != sizeof(uint64_t))
               handle_error("read");

           tot_exp += exp;
           printf("read: %llu; total=%llun",(unsigned long long) exp,(unsigned long long) tot_exp);
       }
    //Do something else ?
    //while(1);
       exit(EXIT_SUCCESS);
   }

编辑
我还有一个问题.
在上面的代码中更改这些行

new_value.it_interval.tv_sec = 5;
   new_value.it_interval.tv_nsec = 0;

至

new_value.it_interval.tv_sec = 0;
   new_value.it_interval.tv_nsec = 5000000000;

我看到没有5秒的延迟,这里发生了什么？