From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <48AEE03E.1080607@domain.hid> Date: Fri, 22 Aug 2008 17:50:22 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <48AEBA77.2040608@domain.hid> <48AEC742.4090902@domain.hid> <48AEC8DC.20406@domain.hid> <48AECCAD.7030405@domain.hid> <48AED396.3040903@domain.hid> <48AED454.3050701@domain.hid> <48AED7A4.20604@domain.hid> <48AED929.8040708@domain.hid> In-Reply-To: <48AED929.8040708@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] [PATCH] userspace: Make CONFIG_SMP default List-Id: "Xenomai life and development \(bug reports, patches, discussions\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai-core Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> 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. > > asm/xenomai/features.h does convert the configure.in options into the > kernel "namespace" options. But it seems that CONFIG_SMP is directly set > by configure.in anyway. > >> Jan - who seems to have run into alignment issues of cmpxchg on x86_64 > > pthread_mutex_lock uses xnheap_alloc to allocate the piece of memory > used for the mutex. So, if the piece of memory is not eight bytes > aligned, this is xnheap_alloc's fault... Maybe it's far simpler: XNARCH_HAVE_US_ATOMIC_CMPXCHG - where the heck does this come from? I just thought I only forgot to define it for x86_64, but I don't find any traces for 32-bit as well. Hmm, should this be called "CONFIG_XENO_FASTSEM" now? Testing... Jan -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux