[Xenomai-help] Re: Re: What happens if task entry function returns?

["M. Koehrer" <mathias_koehrer@domain.hid>]

Hi Jan, 

First, I give you some more information about the error.
The output is the following:
Hi, I am task A Hello
Hi, I am task B World
Main waits for A
This is the end of A
Main waits for B

Then the system hangs.

I have done two tests to verify if there is an SMP issue.
First, I have set all CPUs in use with the application to CPU 0.
There was no change. However, I am able to stop the application with CTRL-C
and everything is cleaned up fine.

Then, I have modified the BIOS settings of the PC to disable Hyperthreading.
Again, no change. The same effect as with the test before.

The strange thing here is, when I use the original test (main on CPU 0, rt tasks on CPU 1)
on a SMP machine, I am not able to terminate the application with CTRL-C.
I have to reboot the PC.

That means, there seems to be a relation to SMP...

Another thing I have detected:
When I modify the program to replace the final rt_task_delete by
a sleep(1) call everything runs perfectly again.

Mathias

> > I found out, that is issue seems to be related to the NPTL (native posix
> thread library).
> > The pthread library in use was 
> > /lib/tls/i686/cmov/libpthread.so.0
> > which is part of the Debian (testing) package libc6-i686.
> > (see http://packages.debian.org/testing/libs/libc6-i686)
> > 
> > When renaming the lib/tls to lib/tls.disabled the pthread library in use
> is
> > /lib/libpthread.so.0
> > and then it is working perfectly!
> 
> ...which does not yet explain WHY the other scenario fails.
> 
> > 
> > It seems that the i686 optimized libc is not fully compatible with
> Xenomai.
> 
> That's not true in such a common form. We are using NTPL libs for i586
> and i686 (SuSE builds) without /general/ issues. Still, specific
> problems like this may sleep somewhere.
> 
> > I read about this library at Romain Lenglet's web page:
> >
> http://www.csg.is.titech.ac.jp/~lenglet/howtos/realtimelinuxhowto/index.html
> 
> > I think this library uses the NPTL (Native Posix Thread Lib).
> > The i686 optimized library shows the value
> > NPTL 2.3.6  
> > at 
> > getconf GNU_LIBPTHREAD_VERSION
> > The "old" pthread lib shows the value:
> > linuxthreads-0.10
> > 
> > Now, I tried to reconfigure Xenomai with --enable-x86-sep to use
> > the NPTL but this did not help either.
> 
> That only influences the way syscalls are passed down into the kernel.
> 
> > When I rename now  /lib/tls to /lib/tls.disabled, the application
> complains
> > about the missing NPTL support in the library.
> > Well, I have now a solution that works:
> > I can use the standard pthread lib and not the i686 optimized NPTL.
> > However, as NPTL seems to be a performance benefit, I think it could be
> > worth to get this combination up and running.
> > 
> > Is there anybody out there that uses a Debian based system with the i686
> > optimized libc that works perfectly?
> > 
> > BTW: I am using xenomai 2.2.4 from end of October.
> > 
> 
> Again my question: is the issue SMP related?
> 
> Reproducing your problem over a qemu box (with or without SMP) failed so
> far for me. But I'm not on your glibc.
> 
> Jan


-- 
Mathias Koehrer
mathias_koehrer@domain.hid


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