change kthread priority

[loody]

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?
BR,
cckuo
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