Re: [Xenomai-core] Re: POSIX include problem

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

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Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>  > ...
>  > I found this while trying Thomas Gleixner's cyclic test over the POSIX
>  > skin (http://www.tglx.de/projects/misc/cyclictest). After fixing a
>  > rather ugly bug in his code (missing mlockall) I ran into a yet unknown
>  > issue with the POSIX skin: the code just hangs when wrapped to Xenomai.
>  > 
>  > Compilation:
>  > gcc -o cyclictest cyclictest.c <posix-cflags> <posix-ldflags>
>  > 
>  > Invocation:
>  > cyclictest -n -p 99
>  > 
>  > Maybe its just real-time starvation (but the watchdog doesn't trigger,
>  > and I do not see why it should starve), maybe its a crash (will try to
>  > attach a serial console later). Anyway, it's an easy test case (and also
>  > a nice tool), so you may want to have a look as well.
> 
> A second, better guess: the created thread is not a Xenomai realtime
> thread, so never suspends (Xenomai calls return EPERM when not called
> from a real-time thread) and hangs. Replacing sched_setscheduler with
> pthread_setschedparam should solve this issue.

Haven't tried this yet, but I'm quite sure that this is the reason. Then
this must have been a classic Linux SCHED_FIFO lock-up.

> 
> I would not be surprised if, with NPTL, sched_setscheduler had an effect
> on the whole process, i.e. set the priority of all the threads in the
> process.
> 

From reading the POSIX spec, I would say the calling sched_setscheduler
multiple times in individual threads indicates a wrong usage, doesn't
it? And what NPTL does with it, specifically in the presence of multiple
threads, is a good questions...

Jan


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