Re: [Xenomai-help] Replacement of taskDelay(0) call

[Johan Borkhuis <j.borkhuis@domain.hid>]

Philippe Gerum wrote:
> On Fri, 2007-10-19 at 16:32 +0200, Johan Borkhuis wrote:
>   
>> When using VxWorks we used "taskDelay(0)" to invoke the scheduler. 
>> Within Xenomai this call was translated into "rt_task_yield()". However,
>>     
>
> You mean xnpod_yield(), the VxWorks skin is directly based on the
> Xenomai abstract core, not on the native skin.
>   
I am not using the VxWorks skin: we were already using an OS-abstraction 
layer for our application, and the Xenomai version of this is based on 
the Native skin.

>>  
>> when using a number of tasks at the same priority using this mechanism 
>> the watchdog timeout kicks in and kills the Xenomai task(s).
>>     
>
> Well, that's the point of the watchdog. If you application does not
> reliquish enough CPU time to the regular Linux kernel activities, the
> system is wil have a problem sooner or later. taskDelay(0) will perform
> some kind of manual round-robin scheduling, therefore doing so among one
> or several real-time tasks for a long time could indeed prevent Linux to
> grab the CPU. In that case, the watchdog really notifies you from a
> problem with the dynamics of your application.
>
> IOW, what is allowed with a dedicated RTOS controlling the whole
> hardware may not be valid in the context of a GPOS and a RTOS sharing
> the same hardware, which is the case with Xenomai. You have to make sure
> Linux has some time left to perform the regular housekeeping duties
> (process non real-time device interrupts, Linux scheduler ticks and so
> on).
>   

Thank you for this extensive explanation. I am afraid that I am still 
thinking to much in terms of a one-OS system and not considering the 
problems that a dual-OS is causing. I will need to look at this problem 
more closely, and see in which way I can change the behavior.

Kind regards,
    Johan Borkhuis