Hi,
For a real-time process, its priority is indicated by the
rt_priority field of the task_struct of the process. I have several
questions about it.
1. The range of value that can be taken by rt_priority is from 1 to
99. I think, for a specific real-time process, it should be located at
some level of runqueue which also ranges from 1 to 99. So, the level
of this real-time process should be determined by its rt_priority
field. But, in scheduler_tick() function,
if ((p->policy == SCHED_RR) && !--p->time_slice) {
2446 p->time_slice = task_timeslice(p);
2447 p->first_time_slice = 0;
2448 set_tsk_need_resched(p);
2449
2450 /* put it at the end of the queue: */
2451 requeue_task(p, rq->active);
2452 }
when a process whose schedule policy is round robin uses up its time
slice, the function put the process at the end of the level. The
requeue_task() function is as follows:
587static void requeue_task(struct task_struct *p, prio_array_t *array)
588{
589 list_move_tail(&p->run_list, array->queue + p->prio);
590}
It is obvious that when entering the runqueue again, the level of the
process is determined by its dynamic priority. So, which one of the
two priorities, namely real-time priority and dynamic priority, will
determine a real-time process' level in a runqueue?
2. I guess that for a real-time process, the dynamic priority may be
equivalent to the real-time priority. If so, the dynamic priority
shouldn't vary for the real-time process. But, when the process is
being waken up, the try_to_wake_up() function will call the
recalc_task_prio() function indirectly, which will cause the dynamic
priority to change. Is my guess wrong?
3. Eventually, I wonder what is the meaning of dynamic priority for a
real-time process and whether there is some relationship between the
dynamic priority and the real-time priority.
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