Linux內核線程實時獲取調度狀態的方法

   最近在做項目中，需要線程實時的知道自身被sched out 和sched in. 查看了schedule()函數實現，發現內核提供了對應的notifier機制.

1.進程sched out流程

schedule->__schedule->context_switch->prepare_task_switch->

fire_sched_out_preempt_notifiers->__fire_sched_out_preempt_notifiers:

static void
__fire_sched_out_preempt_notifiers(struct task_struct *curr,
				   struct task_struct *next)
{
	struct preempt_notifier *notifier;
        /*調用curr註冊的notifier，通知當前進程被sched out */
	hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
		notifier->ops->sched_out(notifier, next);
}

2.進程sched in

schedule->__schedule->context_switch->finish_task_switch->

fire_sched_in_preempt_notifiers->

static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
	struct preempt_notifier *notifier;
        /*通知進程sched in  */
	hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
		notifier->ops->sched_in(notifier, raw_smp_processor_id());
}

3. notifier註冊

Linux內核提供API爲當前進程註冊調度notifier

void preempt_notifier_register(struct preempt_notifier *notifier)

void preempt_notifier_unregister(struct preempt_notifier *notifier)

void preempt_notifier_inc(void)

void preempt_notifier_dec(void)

notifer_register實現如下:

void preempt_notifier_register(struct preempt_notifier *notifier)
{
	if (!static_branch_unlikely(&preempt_notifier_key))
		WARN(1, "registering preempt_notifier while notifiers disabled\n");
        /*把notifer加到當前進程preempt_notifier鏈表*/
	hlist_add_head(&notifier->link, &current->preempt_notifiers);
}

4.任意進程調度監聽

preempt_notifier_register函數只能爲當前進程註冊調度notifier,可以進行適當修改，從而註冊任意進程調度Notifier
 

int task_notifier_register(struct preempt_notifier *notifier,pid_t pid)
{
    struct pid *pid ;
    struct task_struct *task ;

    pid = find_get_pid(pid);
    if(!pid)
        return -EIO ;
    task = get_pid_task(pid,PIDTYPE_PID);
    if(!task)
        return -EIO ;
    hlist_add_head(&notifier->link, &task->preempt_notifiers);
    return 0;
}

5. 用途

1.需要關注進程調度的特定場景,如指令數據採集

2. 用於安全領域進程之間的對抗