Re: [Xenomai-help] Thread policy and priority in secondary mode

[Philippe Gerum <rpm@xenomai.org>]

roderik.wildenburg@domain.hid wrote:
>>>> __real_pthread_setschedparam(). Note: this will propagate the 
>>>> priority to the underlying Xenomai thread as well.
>>>>
>>> Does this mean that the Xenomai thread will run with the new (Linux)
>>> priority when it returns to primary mode ?
>> Yes. However, the propagation only occurs when the skin and Linux have
>> compatible priority scales, which is the case with the POSIX skin.
>>
>>> And the other way round :
>>> when a posix thread switches to secondary mode (without using
>>> __real_pthread_setschedparam), does it run in Linux with 
>> the priority
>>> set in Xenomai (with pthread_setschedparam)?
>> Yes.
>>
>>> Or better : what is the Linux-prority when a Xenomai thread 
>> (posix or or
>>> any other Xenomai thread)switches to secondaary mode ?
>>>
>> It depends on the skin. When the priority scales are 
>> compatible (i.e. a given
>> priority level exists in both and scales are both upwarding, 
>> like POSIX skin <->
>> Linux, and native skin <-> Linux), you get the same priority 
>> level in both
>> modes, and changing the priority from one mode affects the 
>> other mode as well.
>>
>> When they are not compatible, the skin-based priority is 
>> "normalized" and
>> applied to the Linux side when needed (e.g. when VxWorks 
>> taskPrioritySet() is
>> invoked), but __real_pthread_setschedparam does not trigger 
>> the converse
>> propagation (since 2.4.4 actually, because experience showed 
>> that propagating in
>> that case made little sense, and would beget weird 
>> behaviours). The way priority
>> levels are normalized depends on the skin.
>>
> 
> Do you know how a Linux priority, set with pthread_setschedparam
> (real_pthread_setschedparam),
> correlates with the priorities shown by "ps l". In our case we realized
> that ps does not show the priority set with pthread_setschedparam. Is
> there a command which shows the "real" priority ?
>

Try this:
 ps -eo pid,tid,class,rtprio,pri,stat,comm

The priority level you want to look at is listed under the RTPRIO column, not
the PRI one.

Xenomai-wise, do
$ cat /proc/xenomai/sched
The first value of the PRI field (== ps's RTPRIO) is the priority value
according to the nucleus core (0-257 range); when skin priority levels have to
be normalized to fit the Linux scale, a second value between parenthesis is
appended, giving the original, non-converted, level set by the skin.

> Best regrads
> Roderik
> 
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-- 
Philippe.