[Xenomai] Q on scheduling - rt_task_wait_period vs rtdm_wait_event

[Xenomai] Q on scheduling - rt_task_wait_period vs rtdm_wait_event

[Michael Haberler]

so far  we had multiple periodic RT threads of different priority, so a
lower-priority thread would not preempt a higher-priority one

we are switching the scheduling of a low-priority thread from periodic to
event-based - instead of rt_task_wait_period(), this task will now wait in
an RTDM driver ioctl in rtdm_event_wait()

I assume the following to be true:

even if the rtdm_even_wait() terminates while a higher priority thread is
running, the lower priority thread will not be scheduled until all
higher-priority threads have entered rt_task_wait_period().

correct?

thanks in advance,

Michael

background: we're synchronizing an RT thread to an external timing
reference, for now a GPIO interrupt, starting from here:
https://github.com/mhaberler/gpio-irq-rtdm

Re: [Xenomai] Q on scheduling - rt_task_wait_period vs rtdm_wait_event

[Philippe Gerum]

On 06/07/2015 02:39 PM, Michael Haberler wrote:
> so far  we had multiple periodic RT threads of different priority, so a
> lower-priority thread would not preempt a higher-priority one
> 
> we are switching the scheduling of a low-priority thread from periodic to
> event-based - instead of rt_task_wait_period(), this task will now wait in
> an RTDM driver ioctl in rtdm_event_wait()
> 
> I assume the following to be true:
> 
> even if the rtdm_even_wait() terminates while a higher priority thread is
> running, the lower priority thread will not be scheduled until all
> higher-priority threads have entered rt_task_wait_period().
> 
> correct?
> 

Yes, assuming SCHED_FIFO for all of these threads. There is no reason
for implicitly changing the priority of a sleeper as a result of waking
it up from a blocking service.

-- 
Philippe.

Re: [Xenomai] Q on scheduling - rt_task_wait_period vs rtdm_wait_event

[Michael Haberler]

> Am 07.06.2015 um 16:42 schrieb Philippe Gerum <rpm@xenomai.org>:
> 
> On 06/07/2015 02:39 PM, Michael Haberler wrote:
>> so far  we had multiple periodic RT threads of different priority, so a
>> lower-priority thread would not preempt a higher-priority one
>> 
>> we are switching the scheduling of a low-priority thread from periodic to
>> event-based - instead of rt_task_wait_period(), this task will now wait in
>> an RTDM driver ioctl in rtdm_event_wait()
>> 
>> I assume the following to be true:
>> 
>> even if the rtdm_even_wait() terminates while a higher priority thread is
>> running, the lower priority thread will not be scheduled until all
>> higher-priority threads have entered rt_task_wait_period().
>> 
>> correct?
>> 
> 
> Yes, assuming SCHED_FIFO for all of these threads. There is no reason
> for implicitly changing the priority of a sleeper as a result of waking
> it up from a blocking service.

thanks! yes, SCHED_FIFO used here. Just preventing a possible blunder ;)


> 
> -- 
> Philippe.