[Linux kernel] Real-time scheduling class ⑦ (source code analysis of real-time scheduling class core function | dequeue_task_rt function | remove process from the execution queue)

In this blog, start to analyze the function source code pointed to by each function pointer in the struct sched_class rt_sched_classstructure variable;

rt_sched_classThe structure is defined in the linux-5.6.18\kernel\sched\rt.csource , and the core real-time scheduling are also defined in the source code;

1. The dequeue_task_rt function (remove the process from the execution queue)

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Introduction to the dequeue_task_rt function:

dequeue_task_rtThe function is used to update the "scheduling information" ,

remove the "real-time scheduling entity" sched_rt_entity from the "execution queue" (red-black tree) ,

Then add the deleted "real-time scheduling entity" to the end of the "execution queue" (red-black tree) ;

Analysis of dequeue_task_rt function:

update_curr_rt(rq);The function is to update the "scheduling information" ,

dequeue_rt_entity(rt_se, flags);The function is to delete the "real- time scheduling entity" rt_se from the "execution queue" (red-black tree) , and add the deleted "real-time scheduling entity" to the end of the "execution queue" (red-black tree) ;

dequeue_pushable_task(rq, p);The role is to remove the process from the hash table ;

dequeue_task_rt function source code:

static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
{
    
    
	struct sched_rt_entity *rt_se = &p->rt;

	update_curr_rt(rq);
	dequeue_rt_entity(rt_se, flags);

	dequeue_pushable_task(rq, p);
}

Source code path: linux-5.6.18\kernel\sched\rt.c#1381

Two, update_curr_rt function (update scheduling information)

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update_curr_rt(rq);The role is to update the "scheduling information" ;

update_curr_rt function source code:

/*
 * Update the current task's runtime statistics. Skip current tasks that
 * are not in our scheduling class.
 */
static void update_curr_rt(struct rq *rq)
{
    
    
	struct task_struct *curr = rq->curr;
	struct sched_rt_entity *rt_se = &curr->rt;
	u64 delta_exec;
	u64 now;

	if (curr->sched_class != &rt_sched_class)
		return;

	now = rq_clock_task(rq);
	delta_exec = now - curr->se.exec_start;
	if (unlikely((s64)delta_exec <= 0))
		return;

	schedstat_set(curr->se.statistics.exec_max,
		      max(curr->se.statistics.exec_max, delta_exec));

	curr->se.sum_exec_runtime += delta_exec;
	account_group_exec_runtime(curr, delta_exec);

	curr->se.exec_start = now;
	cgroup_account_cputime(curr, delta_exec);

	if (!rt_bandwidth_enabled())
		return;

	for_each_sched_rt_entity(rt_se) {
    
    
		struct rt_rq *rt_rq = rt_rq_of_se(rt_se);

		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
    
    
			raw_spin_lock(&rt_rq->rt_runtime_lock);
			rt_rq->rt_time += delta_exec;
			if (sched_rt_runtime_exceeded(rt_rq))
				resched_curr(rq);
			raw_spin_unlock(&rt_rq->rt_runtime_lock);
		}
	}
}

Source code path: linux-5.6.18\kernel\sched\rt.c#994