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

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

Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
> 
>>Jan Kiszka wrote:
>>
>>>RAKOTOSALAMA, Nirilanto wrote:
>>>
>>>
>>>>Hi,
>>>>
>>>>I'm still blocked on a CPU affinity problem.
>>>>In order to adapt a set affinity function which is based on
>>>>posix linux lib :
>>>>- CPU_AssignPID(uint32 PID, uint32 CPU_id)
>>>>- the cpu affinity of the caller and all its child threads must be set to CPU_id.
>>>>
>>>>Problems are:
>>>>Child PIDs must be listed, the only means I found is listing pids using `ls /proc/"Parent pid"/ > temp_file`
>>>>And each listed pid is sched_setaffinity'ed.
>>>>I don't know if setting affinity of RT threads from an other thread (parent) using pid works with xenomai.
>>>
>>>It works in so far as the Xenomai thread will not change its CPU until
>>>it enters secondary mode. Moreover, there is no explicit "hey, RT thread
>>>x, go to CPU #n!" under the POSIX skin. Migration always go through
>>>secondary mode.
>>
>>Let's repeat it, rephrased, once again: what works with Linux regarding
>>CPU affinity also works with Xenomai.
> 
> 
> To my understanding, there is difference in the behaviour of
> sched_setaffinity() when used on a foreign pid/tid depending on if the
> target is a Xenomai thread in primary mode or if it is a Linux thread,
> no? If this matters in practice, that's a different question (I don't
> think it does, for the reasons given earlier).

True. What we would need is an I-pipe event generated when setting the
affinity of a thread which has the PF_EVNOTIFY flag, we would handle
this event in shadow.c by calling xnpod_migrate_thread. But we need an
asynchronous event to be posted to the thread, for the case when we do
not migrate the current thread.

-- 
                                                 Gilles Chanteperdrix