Hi Parmenides...
let's see what I can help here...
On Wed, Nov 24, 2010 at 03:21, Parmenides <mobile.parmenides@xxxxxxxxx> wrote:
> 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.
Yes, AFAIK for each priority, there should be separate queue....thus
to avoid lengthy lookup.
>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?
>
AFAIK, for real time process, the priority is always
fixed....hopefully CFS doesn't change that agreement...that's how
POSIX decides about real time process AFAIK.
> 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?
yes, only for SCHED_OTHER process, the dyn prio is recalculated.
> 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.
IMO, dynamic priority, in the meaning that "constantly adjusted prio
according to current system load" isn't a concern for a real time
process.
--
regards,
Mulyadi Santosa
Freelance Linux trainer and consultant
blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com
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