Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Gilles Chanteperdrix wrote:
>>> Jan Kiszka wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> Jan Kiszka wrote:
>>>>>> Hi Gilles,
>>>>>>
>>>>>> here is a trivial test case on my desk that points to SCHED_RR issues of
>>>>>> the POSIX skin: simple pthread_create with an attribute block that has
>>>>>> SCHED_RR set, but neither SCHED_RR nor the priority reach the new thread.
>>>>>>
>>>>>> The way the scheduling policy and parameters get to that user space
>>>>>> thread leads via __real_pthread_setschedparam after
>>>>>> __pse51_thread_create. This triggers do_setsched_event in shadow.c. But
>>>>>> here we filter out all policies except for SCHED_FIFO. So neither the
>>>>>> priority nor the required XNRRB flag make it to the target therefore.
>>>>>>
>>>>>> Even worse, we are running aperiodic timer mode, so this would not have
>>>>>> worked anyway due to the scheduler limitations. Fortunately, it turned
>>>>>> out that the customer is fine with SCHED_FIFO as well, but the broken
>>>>>> priorities and/or lacking error codes on creation are annoying + the
>>>>>> fact that it likely wouldn't work even with periodic timer mode.
>>>>> The fact that it does not work with aperiodic timer is documented.
>>>>> However, this used to work and was tested with periodic timer (you can
>>>>> find the tests under sim/skins/posix/testsuite), that is why there is no
>>>>> reason to return any error code.
>>>> ...which is bogus IMHO. Expecting to read the doc when something does
>>>> not work as expected is ok. But more or less silently failing even if it
>>>> is documented that it will somehow fail is not what Xenomai is usually
>>>> known for.
>>>>
>>>> That said, I still don't see (looking at TRUNK) how SCHED_RR should work
>>>> even under periodic mode. Guess I have to enable and test it.
>>>>
>>>> But I guess the best we can do is to finally remove this limitation by
>>>> allowing the use to create a periodic tick timer over aperiodic mode if
>>>> there is a need for RR scheduling.
>>> In ksrc/skins/posix/syscall.c, function __pthread_create:
>>>
>>>         pthread_attr_init(&attr);
>>>         attr.policy = p->policy;
>>>         param.sched_priority = p->rt_priority;
>>>         attr.detachstate = PTHREAD_CREATE_DETACHED;
>>>
>>> So, the priority and policy are taken from the underlying Linux thread.
>> Yep, but its prio/policy is set *after* the chunk above. Maybe it is
>> already a sufficient hot-fix to move __real_pthread_setschedparam before
>> __pse51_thread_create if this has no unwanted side effects.
> 
> Useless. Since do_setsched_event ignores the priority change, everything
> should work as expected.
> 

Don't get what you mean.

Anyway, that reordering doesn't work for shadow threads as they do not
go through xnpod_start_thread from pthread_create, so the XNRRB is not
applied this way.

Thus the only fix to get SCHED_RR working again is to call
__wrap_pthread_setschedparam (or some extract of it) from
__pthread_trampoline, as you suggested. That works, but I cannot asses
right now if it may have side effects.

Jan

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