計算動態優先順序 — effective_prio()

effective_prio()函數返回進程p的動態優先順序
static int effective_prio(task_t *p)
{
    int bonus, prio;

如果進程p是個即時進程，那麼直接返回該即時進程的prio(即時進程的動態優先順序prio不依賴於靜態優先順序static_prio，兩者是否相等???)
|----------------------------|
|   if (rt_task(p))          |
|       return p->prio;      |
|----------------------------|

計算紅利bonus:
|---------------------------------------------|
|   bonus = CURRENT_BONUS(p) - MAX_BONUS / 2; |
|---------------------------------------------|

根據如下公式計算該進程動態優先順序prio:
prio = max ( 100, min(static_prio - bonus + 5, 139) )
|------------------------------------|
|   prio = p->static_prio - bonus;   |
|   if (prio < MAX_RT_PRIO)          |
|       prio = MAX_RT_PRIO;          |
|   if (prio > MAX_PRIO-1)           |
|       prio = MAX_PRIO-1;           |
|------------------------------------|
    return prio;
}