[Xenomai-core] Questio about the Xenomai Scheduler

[Xenomai-core] Questio about the Xenomai Scheduler

[Jan-Erik Lange]

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Hello,
 
I have a question about the Xenomai scheduler.

Can the Xenomai Scheduler always preempt any operation of the scheduler of the standard Linux kernel? What is, when a migrated RT-Task
is currently scheduled by the standard Linux scheduler? Does the Xenomai Scheduler can preempt this task too?
 
Best regards 
Jan 		 	   		  

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Re: [Xenomai-core] Questio about the Xenomai Scheduler

[Jan-Erik Lange]

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 Is it perhaps this way?: 
 
When the RT-Task migrated into the secondary domain, it is scheduled by the Linux-Scheduler:
 
-> It inherits the RT-priority from her life in the primary domain and is timely priviliged compared to other tasks scheduled by the linux scheduler, which have a lower priority.
-> But it can always be preempted by an RT-Task, that runs in the primary domain and that is scheduled by the Xenomai Scheduler, because this scheduler can preempt all
standard linux kernel activities.
-> Still it is protected from preempting by an Linux interrupt handler, because the I-Pipe is block the interrupts.
 



From: jan0385@domain.hid
To: xenomai@xenomai.org
Date: Sat, 7 Jan 2012 11:43:15 +0100
Subject: [Xenomai-core] Questio about the Xenomai Scheduler





Hello,
 
I have a question about the Xenomai scheduler.

Can the Xenomai Scheduler always preempt any operation of the scheduler of the standard Linux kernel? What is, when a migrated RT-Task
is currently scheduled by the standard Linux scheduler? Does the Xenomai Scheduler can preempt this task too?
 
Best regards 
Jan

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Re: [Xenomai-core] Questio about the Xenomai Scheduler

[Gilles Chanteperdrix]

On 01/08/2012 01:06 PM, Jan-Erik Lange wrote:
> 
> Is it perhaps this way?:
> 
> When the RT-Task migrated into the secondary domain, it is scheduled
> by the Linux-Scheduler:
> 
> -> It inherits the RT-priority from her life in the primary domain
> and is timely priviliged compared to other tasks scheduled by the
> linux scheduler, which have a lower priority.

No, a linux task with a higher priority than the RT task running in
secondary mode may preempt the RT task running in secondary mode.

> -> But it can always be
> preempted by an RT-Task, that runs in the primary domain and that is
> scheduled by the Xenomai Scheduler, because this scheduler can
> preempt all standard linux kernel activities. 

Yes if root priority inheritance is disabled, not if it is enabled (the
default).

> -> Still it is
> protected from preempting by an Linux interrupt handler, because the
> I-Pipe is block the interrupts.

No, this used to be true a long time ago, but is no longer the case.

You have to consider that an RT task running in secondary mode is an
ordinary linux task. Only tasks remaining in primary mode are deterministic.

-- 
                                                                Gilles.