3.2调度

硬件时钟中断，需要处理非紧急时钟事务时，调度softclock，以便在响应完硬件时钟中断后运行softclock。

代码:

/*
* The real-time timer, interrupting hz times per second.
*/
void
hardclock(frame)
  register struct clockframe *frame;
{
  ......

  if (need_softclock)
    swi_sched(softclock_ih, 0);

  ......
}

/*
* Schedule a heavyweight software interrupt process.
*/
void
swi_sched(void *cookie, int flags)
{
  struct intrhand *ih = (struct intrhand *)cookie;
  struct ithd *it = ih->ih_ithread;
  int error;

  atomic_add_int(&cnt.v_intr, 1); /* one more global interrupt */
    
  CTR3(KTR_INTR, "swi_sched pid %d(%s) need=%d",
    it->it_td->td_proc->p_pid, it->it_td->td_proc->p_comm, it->it_need);

  /*
  * Set ih_need for this handler so that if the ithread is already
  * running it will execute this handler on the next pass. Otherwise,
  * it will execute it the next time it runs.
  */
  atomic_store_rel_int(&ih->ih_need, 1);
  if (!(flags & SWI_DELAY)) {
    error = ithread_schedule(it, !cold && !dumping);
    KASSERT(error == 0, ("stray software interrupt"));
  }
}