Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Gilles Chanteperdrix wrote:
>>> Jan Kiszka wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> Jan Kiszka wrote:
>>>>>> Disabling SMP (on platforms where this isn't off by design already) is
>>>>>> an optimization. In contrast, not enabling it by default is doomed to
>>>>>> cause problems for users that run ./configure without looking into each
>>>>>> and every switch - now that CONFIG_SMP is very important for all the
>>>>>> fast locking stuff.
>>>>> I would consider setting CONFIG_SMP by default on x86... because on some
>>>>> other architectures like arm, it is not even yet a valid configuration.
>>>> But it is on PowerPC or IA64. Would it cause troubles for the
>>>> non-SMP-ready archs? Then we can disable it on those selectively.
>>> Are you sure that the lock prefix on an UP x86 or lsync on an UP powerpc
>>> is hamrless ?
>> LOCK is harmless (except for potential overhead), can't comment isync,
>> but I strongly suspect the same (locking at the glibc e.g.). There is a
>> simple idea behind this: Do you have to install a special glibc in order
>> to enable/disable SMP support?
>>
>> [ BTW, I think the current pthread_mutex implementation lacks the LOCK
>> prefix even in SMP mode due to include issues. Will get fixed with my
>> patches under preparation, which also unifies that stuff on x86. ]
> 
> Should be easy to check, disassemble pthread_mutex_lock with CONFIG_SMP
> enabled.
> 
> You mean we should include asm/xenomai/features.h before using CONFIG_SMP ?

That helps as well - I added xeno_config.h explicitly so far, but
features.h implies xeno_config.h, of course.

Jan - who seems to have run into alignment issues of cmpxchg on x86_64

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux

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