Re: Changing Kernel thread priorities

[Monica Puig-Pey]

El 07/06/11 10:27, Johannes Bauer escribiÃ:
> Absolutly correct!
>
> However, if you are running the system on an embedded platform, where the _WHOLE_ system (including priorities) is preconfigured and never touched, starting a irq thread with the right prio from start is a more straightforward method than having to invoke a script that changes it using userspace chrt tool.
>
> Regards JB
> ----- UrsprÃngliche Nachricht -----
> Von: "Peter Zijlstra"<peterz@xxxxxxxxxxxxx>
> Erhalten: 07.06.2011 00:36
> An: hannes_bauer@xxxxxx
>
> "Monica Puig-Pey" wrote:
> > I need to change the priority from inside the driver, when creating the
> > kernel thread.
>
> No you don't. How does you driver know about what priority is correct
> wrt all the other running RT tasks on the system?
>
> Determining the right priority in a fixed priority scheduling system is
> a system wide problem, nobody but the administrator can possibly even
> begin to solve it.
>
> There's a reason all RT irq threads are started at 50, its plain
> impossible to do better.

That's it!
If I work with embedded system where I know all my tasks running and 
there is not a user how could I do it?

What I tried is create the kernel thread in my init_module using:

	#include <linux/kthread.h>

	struct task_struct *kthread_create(int (*threadfn)(void *data),
				   void *data,
				   const char namefmt[], ...)
and then running it with:

	#include <linux/sched.h>
	
	extern int wake_up_process(struct task_struct *tsk);

These functions stars a Kthread which has a NON RT priority. I can see 
this using the ps command from user space.
Because it's not a real time thread is why I want, better need, to 
change its priority, to have only real time threads running in my 
driver. I want to use the Kthread as a bottom half for the interrupts.

How could I create real time kernel threads then? is kthread_create 
wrong for real time enviroment?


--
__________________________________________________________________________________

MÃnica Puig-Pey GonzÃlez       E-mail: puigpeym@xxxxxxxxx

Grupo de Computadores y Tiempo Real, Departamento de ElectrÃnica y 
Computadores.
Facultad de Ciencias - Universidad de Cantabria
Av. de los Castros s/n. 39005 - Santander, EspaÃa
__________________________________________________________________________________
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