Re: [Xenomai-help] pthread cancelation and scheduling magics

[Wolfgang Grandegger <wg@domain.hid>]

Jan Kiszka wrote:
> Wolfgang Grandegger wrote:
>> Wolfgang Grandegger wrote:
>>> Hi Gilles,
>>>
>>> Gilles Chanteperdrix wrote:
>>>> Wolfgang Grandegger wrote:
>>>>> I'm also puzzled why pthread_setschedparam() does make a mode switch
>>>>> to secondary mode (sometimes).
>>>> That is normal. The glibc caches threads priority value, so we have to
>>>> call __real_pthread_setschedparam to update them. This issue has been
>>>> solved differently on trunk, but unfortunately, we can not backport this
>>>> modification on v2.4.x branch.
>>> To get you right. With v2.4.x it is not possible with the POSIX skin to
>>> change the priority of a real-time thread in the primary mode without
>>> loosing determinism (because it will switch to secondary mode). What
>>> options do I have?
>> I gave Xenomai trunk a try and pthread_setschedparam() does not switch
>> to secondary mode any more on my PowerPC test system. Nice, I just get
>> an Oops in thread_delete from time to time. More on that issue later.
>> For my ARM i.mx31 system, a need a few patches to get the Xenomai src's
>> compiled:
>>
>> Index: include/asm-generic/bits/bind.h
>> ===================================================================
>> --- include/asm-generic/bits/bind.h	(revision 4450)
>> +++ include/asm-generic/bits/bind.h	(working copy)
>> @@ -72,7 +72,7 @@
>>  	err = XENOMAI_SYSCALL1(__xn_sys_current, &current);
>>  	if (err) {
>>  		fprintf(stderr, "Xenomai: error obtaining handle for current "
>> -			"thread: %s\n", strerror(err));
>> +			"thread: %s\n", strerror(-err));
>>  		exit(1);
>>  	}
>>  	__xeno_set_current(current);
>> Index: include/asm-arm/syscall.h
>> ===================================================================
>> --- include/asm-arm/syscall.h	(revision 4450)
>> +++ include/asm-arm/syscall.h	(working copy)
>> @@ -228,7 +228,7 @@
>>  	volatile unsigned long long *const tscp = __xn_tscinfo.u.fr.tsc;
>>  	volatile unsigned *const counterp = __xn_tscinfo.u.fr.counter;
>>          const unsigned mask = __xn_tscinfo.u.fr.mask;
>> -	register unsigned long long after, before;
>> +	register unsigned long long result;
>>          unsigned counter;
>>  
>>          __asm__ ("ldmia %1, %M0\n": "=r"(result): "r"(tscp), "m"(*tscp));
>>
>>
>> When I then start my application or cyclictest I get:
>>
>> -bash-3.2# ./cyclictest -n 
>> Xenomai: error obtaining handle for current thread: Operation not permitted
>>
>> As the latency program works fine, it seems to be a problem with the
>> POSIX skin. Any idea what it is?
> 
> First of all, are you sure that all parts were properly updated and in
> sync now?

Well, everything (kernel, Xenomai unser-space) was built from scratch
using the latest SVN revision.

> 
> The error means that something went wrong during the
> __wrap_pthread_setschedparam execution on __init_posix_interface. More
> precisely, we lack the shadow thread for the current (main) thread for
> unknown reasons.
> 
> Could you fire up gdb, step through this and check (looking at
> /proc/xenomai/sched) what happens on ARM here? x86 was fine the last
> time I checked (will recheck later today).

With --enable-debug it works just fine :-(.

Wolfgang.