change kthread priority

[loody]

hi:

2011/7/11 Mulyadi Santosa <mulyadi.santosa at gmail.com>:
> Hi...
>
> On Sun, Jul 10, 2011 at  is 17:27, loody <miloody at gmail.com> wrote:
>> Dear all:
>> I have some questions about kthread:
>> 1. can we change kthread priority through user mode program?
>
> Theoritically you can, but only if the priority not fixed and/or you
> have required capability to do so
>
>> 2. I found some functions that may be helpful.
>> sched_getscheduler
>> sched_setscheduler
>>
>> When I use them in user mode, the return value of sched_setscheduler  is fail.
>
> did you do that as root? anything blocking you doing that withing
> SELinux or AppArmor policy?
I execute it as root.
what is "SELinux or AppArmor policy"?

>
>> there is a thread talking about this,
>> http://www.spinics.net/lists/linux-rt-users/msg06588.html
>> What makes me confuse is "these 2 functions is used in user mode or
>> kernel mode?"
>
> 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)
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.)

Thanks for your kind help,