Re: [Xenomai-core] SCHED_RR

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

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.

-- 
                                                 Gilles.