change kthread priority

[santhosh kumars]

On Mon, Jul 11, 2011 at 12:45 PM, loody <miloody at gmail.com> wrote:
> Hi:
>
> 2011/7/11 loody <miloody at gmail.com>:
>> hi:
>>
>>
>> 2011/7/11 Dave Hylands <dhylands at gmail.com>:
>>> Hi Milody,
>>>
>>> On Sun, Jul 10, 2011 at 8:55 PM, loody <miloody at gmail.com> wrote:
>>>> hi:
>>>>
>>>> 2011/7/11 Mulyadi Santosa <mulyadi.santosa at gmail.com>:
>>>>> Hi...
>>>>>
>>>
>>> ...snip...
>>>
>>>>> AFAIK they are user mode libc functions...
>>>> I found there are the same export_symbols in kernel.
>>>> I use them to dynamically change the priority.
>>>> It works but I found something interesting:
>>>> 1. if thread use schedule algorithm of SCHED_NORMAL, it cannot change
>>>> the priority.
>>>> 2. can we set the priority  to any number less than
>>>> (MAX_USER_RT_PRIO-1)?
>>>> ( I tried to set the priority as 99, but it fail)
>>>
>>> You need to change the scheduling algorithim to be SCHED_FIFO or
>>> SCHED_RR in order to use the real-time priorities.
>> I saw kernel restrict the algorithm as SCHED_FIFO and SCHED_RR to
>> change the priority.
>> What are the differences between rt_priority, prio, static_prio and
>> normal_prio?
>> sched_setscheduler seems only change rt_priority.
>>
>> normal_prio is MAX_RT_PRIO-1 - t_priority
>> prio will be min(normal_prio, task_top_pi_waiter)
>>
>> what is the real priority that kthread runs after calling
>> sched_setscheduler ?
>>
>>
>>>
>>>> 3. can we get the name of thread from task_struct or pid?
>>>> (I use "cat /proc/338/status", I can see the name of thread. But I
>>>> look around the task_struct, I cannot find any name information in
>>>> it.)
>>>
>>> You can use the comm field from the task struct. This can be set using
>>> the prctl API and passing in PR_SET_NAME. You can see the task name by
>>> doing something like
>>>
>>> ps -T -o pid,ppid,user,time,comm
>>>
>>> Normally, ps shows the args column.
>>>
>>> --
> Since there are below schedule algorithms in kernel,
> SCHED_NORMAL
> SCHED_FIFO
> SCHED_RR
> SCHED_BATCH
> when and how they circular around?
> or each of them has a fix cpu time slice to go through?
The base scheduler code(kernel/sched.c) iterates over each scheduler
class(SCHED_NORMAL,SCHED_FIFO,SCHED_RR) in order of priority.The
highest priority scheduler class that has a runnable process wins.
below is the code.
/*
* Pick up the highest-prio task:
*/
static inline struct task_struct *
pick_next_task(struct rq *rq)
{
const struct sched_class *class;
struct task_struct *p;
/*
* Optimization: we know that if all tasks are in
* the fair class we can call that function directly:
*/
if (likely(rq->nr_running == rq->cfs.nr_running)) {
p = fair_sched_class.pick_next_task(rq);
if (likely(p))
return p;
}
class = sched_class_highest;
for ( ; ; ) {
p = class->pick_next_task(rq);
if (p)
return p;
/*
* Will never be NULL as the idle class always
* returns a non-NULL p:
*/
class = class->next;
}
}
> BR,
> cckuo
>
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