From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <48AED396.3040903@domain.hid> Date: Fri, 22 Aug 2008 16:56:22 +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> In-Reply-To: <48AECCAD.7030405@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: >>>> 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 -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux