Re: [Xenomai-help] newbie question

[Philippe Gerum <rpm@xenomai.org>]

On Mon, 2007-08-06 at 19:57 +0200, Gilles Chanteperdrix wrote:
> rolfetas bambolas wrote:
>  > Hi to all,
>  > I'm trying to understand how Xenomai handles priorities, and found a paper
>  > called "Life with Adeos" from 2005 which explains that tasks in secondary
>  > mode force the linux kernel to inherit the RT-Tasks priority.
>  > I also read that User-Space RT Tasks migrate to secondary mode when they
>  > make a system call to the linux-kernel, and migrate back when they use some
>  > Xenomai API.
>  > 
>  > Does this mean, that the Linux-Kernel will keep the inherited priority until
>  > the RT-Task calls again Xenomai?? what happens is a RT-Task doesn't call
>  > Xenomai for a while??
>  > I hope you understand what I mean,
>  > Thank you,
> 
> What you are referring to is the priority coupling between Xenomai and
> Linux schedulers, and can be disabled in Xenomai configuration.
> 
> The linux kernel will keep the inherited priority until the RT-task
> calls xenomai again, or until it is suspended by Linux scheduler. If the
> RT-task does not call xenomai for a while (and is not suspended by Linux
> scheduler), then, well, it is an RT-task after all and should be able to
> run until it reaches a suspension point or wakes up another RT-task.
> 
> Note however that during this time, Linux interruptions will be allowed
> to preempt the RT-task.
> 

(unless the interrupt shield is in effect).

-- 
Philippe.