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

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

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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).

Jan


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