fork 优先级_github fork_fork(3)

后来调到__setscheduler() 真正进行进程优先级设置，

/* Actually do priority change: must hold rq lock. */
static void
__setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
{
	p->policy = policy;// 你通过sched_setscheduler()传入的sched policy就是最终赋予给(task_struct*)p->policy
	p->rt_priority = prio;//你通过sched_setscheduler()传入的prio 最终却赋予给了(task_struct*)p->rt_priority，怎么样？ 没忽悠你吧，传入的非实时进程优先级值真的只能是0!!!
	p->normal_prio = normal_prio(p);//接下来看 p->normal_prio 是怎么回事？
	/* we are holding p->pi_lock already */
	p->prio = rt_mutex_getprio(p);
	if (rt_prio(p->prio))
		p->sched_class = &rt_sched_class;
	else
		p->sched_class = &fair_sched_class;
	set_load_weight(p);
}

看下normal_prio()

/*
 * Calculate the expected normal priority: i.e. priority
 * without taking RT-inheritance into account. Might be
 * boosted by interactivity modifiers. Changes upon fork,
 * setprio syscalls, and whenever the interactivity
 * estimator recalculates.
 */
static inline int normal_prio(struct task_struct *p)
{
	int prio;

	if (task_has_rt_policy(p))
		prio = MAX_RT_PRIO-1 - p->rt_priority;//如果你是实时进程，p->prio = 99 - 你通过sched_setscheduler()传入的优先级值，这下明白了吧，watchdog 进程通过sched_setscheduler() 设置的优先级值为99， 这样一算之后真正 p->prio 为0， 也就是linux kernel 中最高优先级的实时进程！
	else
		prio = __normal_prio(p);// 非实时进程的优先级，可真费劲，接着看?
	return prio;
}

看下__normal_prio(),

/*
 * __normal_prio - return the priority that is based on the static prio
 */
static inline int __normal_prio(struct task_struct *p)
{
	return p->static_prio;//逗我呢吧，非实时进程的优先级通过sched_setscheduler()设置的值并没有赋予p->prio，而是直接取的p->static 的值
p->static 的值从哪来的呢？
}

本文来自电脑杂谈，转载请注明本文网址：
http://www.pc-fly.com/a/jisuanjixue/article-40531-3.html