[Xenomai-core] rt_task_create and rt_task delete re-scheduling calling task

[Xenomai-core] rt_task_create and rt_task delete re-scheduling calling task

[Roberto Bielli]

Hi,

i saw in the documentation that rt_task_create and rt_task_delete should 
re-scheduling the calling task.
So i lost the priority if in a task try to call rt_task_create or 
rt_task create. Do i understand correctly ?
Is there a way to avoid this behaviour ? Or which are all the case of 
re-scheduling whne calling rt_task_create/rt_task_delete ?

Thanks of all

P.S.  the imx25 now it's perfect. Was only the reentrant interrupt.

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Roberto Bielli
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Re: [Xenomai-core] rt_task_create and rt_task delete re-scheduling calling task

[Gilles Chanteperdrix]

On 05/14/2012 09:55 AM, Roberto Bielli wrote:
> Hi,
> 
> i saw in the documentation that rt_task_create and rt_task_delete should 
> re-scheduling the calling task.

rt_task_create may reschedule the calling task, only "may", not
"should". And it happens in the obvious case: when creating a task with
a higher priority than the current task.

The reason why rt_task_delete may reschedule is documented:
"Native tasks implement a mechanism by which they are immune from
deletion by other tasks while they run into a deemed safe section of
code. This feature is used internally by the native skin in order to
prevent tasks from being deleted in the middle of a critical section,
without resorting to interrupt masking when the latter is not an option.
For this reason, the caller of rt_task_delete() might be blocked and a
rescheduling take place, waiting for the target task to exit such
critical section."

Xenomai online documentation may be found here:
http://www.xenomai.org/documentation/xenomai-2.6/html/api/index.html

And a local copy is installed when you run xenomai package "make install".


-- 
                                                                Gilles.

Re: [Xenomai-core] rt_task_create and rt_task delete re-scheduling calling task

[Philippe Gerum]

On 05/14/2012 09:55 AM, Roberto Bielli wrote:
> Hi,
>
> i saw in the documentation that rt_task_create and rt_task_delete should
> re-scheduling the calling task.
> So i lost the priority if in a task try to call rt_task_create or
> rt_task create. Do i understand correctly ?
> Is there a way to avoid this behaviour ? Or which are all the case of
> re-scheduling whne calling rt_task_create/rt_task_delete ?

There is no way to avoid rescheduling (assuming you are currently using 
the user-space API). Creating and deleting tasks involves switching to 
secondary mode to get/release linux resources it's impossible to access 
from a primary context.

>
> Thanks of all
>
> P.S. the imx25 now it's perfect. Was only the reentrant interrupt.
>


-- 
Philippe.

Re: [Xenomai-core] rt_task_create and rt_task delete re-scheduling calling task

[Gilles Chanteperdrix]

On 05/14/2012 09:55 AM, Roberto Bielli wrote:
> P.S.  the imx25 now it's perfect. Was only the reentrant interrupt.

By the way, now that Linux runs all interrupt handlers with hardware irq
disabled, this option is completely useless: it will prevent a low
priority irq to interrupt a low priority irq while the high priority
interrupt handler is running, but since that handler is already running
with hardware interrupts off, this does not add anything.

-- 
					    Gilles.