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Date: Thu, 24 May 2007 14:07:38 +0200
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-help] [Newbie question] threads and task CPU affinity
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To: "RAKOTOSALAMA, Nirilanto" <NIRILANTO.RAKOTOSALAMA@airbus.com>
Cc: xenomai@xenomai.org

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RAKOTOSALAMA, Nirilanto wrote:
> Thanks Jan,
>=20
> 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=20
> 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.

>=20
> If not, when I "sched_setaffinity" a parent process, I have to=20
> recursively "sched_setaffinity" all its threads and force them to
> switch to primary mode. Is it right ?

If you want well-defined target CPUs, then you need explicit
sched_setaffinity, cpusets, or Xenomai 2.4's global affinity mask. But
you don't need to switch back to primary mode, that will happen
automatically.

Jan


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