Re: [Xenomai-help] How to use Xenomai libraries with "normal" (non Xenomai) linux processes ?

[Jan Kiszka <jan.kiszka@domain.hid>]

roderik.wildenburg@domain.hid wrote:
> Jan Kiszka wrote:
> 
>>> The point is that if you force it to secondary mode, and 
>> the next system
>>> call is in fact a xenomai syscall, xenomai will switch the thread to
>>> primary mode again. So, you have two useless mode switches which you
>>> could have avoided if you had not forcibly switched to 
>> secondary mode.
>>> Note that even if a xenomai thread is running in secondary 
>> mode and has
>>> a priority higher than another xenomai thread running in 
>> primary mode,
>>> the one running in secondary mode will run. So, you should not use
>>> primary mode and secondary mode to decide which thread 
>> should run, you
>>> should use the priorities.
>> The only imaginable scenario for having to force some thread back to
>> secondary mode is when that thread is running significant CPU load
>> _without_ issuing a single regular syscall. If such a thread enters
>> primary mode and is then left there, Linux will not be able to run
>> anymore. In that case one may insert a tiny nanosleep etc. to enforce
>> the switch. But that's still a fairly theoretic scenario.
>>
> 
> But nanosleep is a Xenomai function. So, after that nanosleep the
> process would return to pimary mode and run in front of all other
> Xenomai tasks (a high priority provided) although it has been just an
> oridnary Linux task (which has been linked with a Xenomai library) and
> therefore should only run when all Xenomai processes yield CPU. Am I
> right? Do you understand my dilemma ?

Yeah, bad example. Take $YOUR_FAVORITE_CHEAP_LINUX_SYSCALL instead, for
instance syscall(SYS_pid) will be better.

Jan

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