Re: [Xenomai-help] [Newbie question] threads and task CPU affinity

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
> RAKOTOSALAMA, Nirilanto wrote:
> 
>>Thanks Jan,
>>
>>It's more and more clear.
>>Just a question, I've a little doubt. Native tasks do not inherit
>>affinity from their parent process. I've read that cpu affinity 
>>setting at pthread creation is only availablle in kernel space.
>>Do Posix skin threads inherit affinity from their parent, in user space?
> 
> 
> IIRC, pthread CPU affinity is not (yet) covered by the POSIX specs, thus
> the behaviour depends on Linux here. Moreover,
> pthread_attr_setaffinity_np support for Xenomai is infeasible due to
> glibc compatibility issues - again: IIRC. Gilles, please correct my weak
> memory on this topic.

Recent versions of glibc have pthread_attr_setaffinity_np as well as
pthread_setaffinity_np. Implementing pthread_attr_setaffinity_np would
mean that we change the pthread_attr_t structure, whereas we currently
use glibc pthread_attr_t, but implementing pthread_setaffinity_np would
be feasible. However, you can use whatever service glibc provides, it
should work with Xenomai.

The only advantage of Xenomai nucleus migration service
(xnpod_migrate_thread) over Linux service (set_cpus_allowed), is that
xnpod_migrate_thread migrates the thread timers as well.

-- 
                                                 Gilles Chanteperdrix