sched_info_arrive()

進程t即將獲得CPU控制權
匯總進程t在可執行隊列上所等候時間的綜合；更新進程t獲得CPU控制權的時間戳記
static inline void sched_info_arrive(task_t *t)
{
    unsigned long now = jiffies, diff = 0;
    struct runqueue *rq = task_rq(t);

    if (t->sched_info.last_queued)
        diff = now - t->sched_info.last_queued;
    sched_info_dequeued(t);
    t->sched_info.run_delay += diff;
    t->sched_info.last_arrival = now;
    t->sched_info.pcnt++;

    if (!rq)
        return;

    rq->rq_sched_info.run_delay += diff;
    rq->rq_sched_info.pcnt++;
}
task_struct.sched_info.last_queued        
    when we were last queued to run(最近一次加入runqueue的時間)
task_struct.sched_info.run_delay        
    time spent waiting on a runqueue(每一次進入runqueue到得到CPU控制權的時間間隔的總和)
task_struct.sched_info.pcnt                
    # of timeslices run on this cpu