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

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

[-- Attachment #1: Type: text/plain, Size: 3083 bytes --]

RAKOTOSALAMA, Nirilanto wrote:
>>> Hello,
>>>
>>> I have some question about CPU affinity with Xenomai 2.3.1.
>>> (it is to see if  xenomai support developing for a cpu 
>> manager library is feasible)
>>
>> What will this library do? (/me just nosy)
> 
> In fact, there's simulation programs that run on many different systems (hard + soft),
> and to make this applications as portable as possible, they use libraries developed for every
> systems (dec alpha, pc, specific cards, linux, unix). And, I search if xenomai could be used
> with less re-implementation effort, so the more posix function are developed by xenomai, 
> the better it is, and easier it is (for me :p).
> So first step is developing this libraries xenomai support (e.g. timer, cpu).
> This cpu library should provides "simple" functions like : getting the number of cpu,
> setting/getting the cpu affinity for a process passing its pid, protect/un-protect cpu from running
> unwanted process.

OK, I see.

> 
>>> When using rt_task_create, CPU mask can be specified. 
>> However, when sched_setaffinity is called 
>>> to modify main program affinity, and after, rt_task_create 
>> is called without specifying CPU mask,
>>> did the child task inherits from the main program affinity ?
>> If you don't provide a target CPU (either on creation or via
>> /proc/xenomai/affinity), better consider the affinity as unspecified
>> (any possible CPU). The target CPU derives from Linux 
>> decision where to
>> put the thread non-RT boot code on, Xenomai just nails that decision
>> down until someone explicitly migrates.
>>
>>> Same question for Posix skin threads ?
>>>
>>> Can native task affinity be set other than when creating ? 
>> using sdhed_setaffinity ?
>>
>> /proc/xenomai/affinity (has global scope) or 
>> sched_setaffinity. Xenomai
>> shadow threads follow the migration that may took place while in
>> secondary mode, and sched_setaffinity comes with such a mode switch.
> 
> Thanks, If I have well understood, tasks or threads affinity can be set using /proc/xenomai/affinity
> but, I have read that /proc/xenomai/affinity does not exist in xenomai 2.3.1 and xenomai must be patched

Yes, it's an upcoming feature of 2.4.

> (I don't know how because I don't have nor SVN neither internet connection on my xenomai boxes).

There is a daily snapshot on gna.org: https://gna.org/svn/?group=xenomai

> So I can use sched_setaffinity, but it make switch to secondary mode. 
> Does'nt matter if only threads must be RT and sched_setaffinity is called during a non-rt init phase, does it ?

Yep.

> That means that affinity does'nt depend on running on xenomai or secondary mode ?

Sorry, doesn't parse for me right now.

> 
> BTW, is protecting a CPU with xenomai possible ? 
> Does xenomai use /dev/cpuset or an other device ?

Xenomai doesn't directly interact with cpuset -- but... if you force
some RT process into a certain CPU and you don't override this decision
on RT thread creation, Xenomai will follow as explained.

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 250 bytes --]