Re: [Xenomai-core] [PATCH] userspace: Make CONFIG_SMP default

[Jan Kiszka <jan.kiszka@domain.hid>]

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. ]

Jan

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