void enqueue(
  register struct proc *rp  /* this process is now runnable */
)
{
/* Add 'rp' to one of the queues of runnable processes.  This function is
 * responsible for inserting a process into one of the scheduling queues.
 * The mechanism is implemented here.   The actual scheduling policy is
 * defined in sched() and pick_proc().
 *
 * This function can be used x-cpu as it always uses the queues of the cpu the
 * process is assigned to.
 */
  int q = rp->p_priority;           /* scheduling queue to use */
  struct proc **rdy_head, **rdy_tail;

  assert(proc_is_runnable(rp));

  assert(q >= 0);

  rdy_head = get_cpu_var(rp->p_cpu, run_q_head);
  rdy_tail = get_cpu_var(rp->p_cpu, run_q_tail);

  /* Now add the process to the queue. */
  if (!rdy_head[q]) {       /* add to empty queue */
      rdy_head[q] = rdy_tail[q] = rp;       /* create a new queue */
      rp->p_nextready = NULL;       /* mark new end */
  }
  else {                    /* add to tail of queue */
      rdy_tail[q]->p_nextready = rp;        /* chain tail of queue */
      rdy_tail[q] = rp;             /* set new queue tail */
      rp->p_nextready = NULL;       /* mark new end */
  }

  if (cpuid == rp->p_cpu) {
      /*
       * enqueueing a process with a higher priority than the current one,
       * it gets preempted. The current process must be preemptible. Testing
       * the priority also makes sure that a process does not preempt itself
       */
      struct proc * p;
      p = get_cpulocal_var(proc_ptr);
      assert(p);
      if((p->p_priority > rp->p_priority) &&
              (priv(p)->s_flags & PREEMPTIBLE))
          RTS_SET(p, RTS_PREEMPTED); /* calls dequeue() */
  }
#ifdef CONFIG_SMP
  /*
   * if the process was enqueued on a different cpu and the cpu is idle, i.e.
   * the time is off, we need to wake up that cpu and let it schedule this new
   * process
   */
  else if (get_cpu_var(rp->p_cpu, cpu_is_idle)) {
      smp_schedule(rp->p_cpu);
  }
#endif

  /* Make note of when this process was added to queue */
  read_tsc_64(&(get_cpulocal_var(proc_ptr)->p_accounting.enter_queue));


#if DEBUG_SANITYCHECKS
  assert(runqueues_ok_local());
#endif
}