On Wed, Aug 28, 2013 at 9:19 AM, Sebastian Huber <sebastian.hu...@embedded-brains.de> wrote: > Hello, > > as part of a GSoC project we made the atomic operations API compatible with > the C11 operations and use them for the implementation. I added some tests > today and now begin to think if this was really such a good idea: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58259 > > Surprisingly it seems that the atomic operations support is not shared by > the C and C++ compiler parts in GCC. > > I just realized that the C11 atomic_flag type has no load operation. This > makes it not suitable to implement a simple test and test and set lock. So > this type is useless for us. The only special thing with atomic_flag is > that it is guaranteed to be lock free. This is the minimum requirement for > atomic operations. > > This leads to the following question: What is the RTEMS (!) minimum > requirement for SMP support? > > I think an architecture must support a compare and swap instruction or the > load linked and store conditional model. We should make it clear that a > simple atomic swap is not enough to support SMP. > To avoid ABA Problem the architecture apparently should have LL/SC or double-word CAS. http://en.wikipedia.org/wiki/ABA_problem
Options moving forward include: * Revert to custom implementations based on upstream *BSD. * Try to fix upstream newlib/gcc code * Use some library like http://concurrencykit.org/ that we looked at before, but it does not support ARM right now. > Under this requirement we can remove the atomic flag from the RTEMS API. > > -- > Sebastian Huber, embedded brains GmbH > > Address : Dornierstr. 4, D-82178 Puchheim, Germany > Phone : +49 89 189 47 41-16 > Fax : +49 89 189 47 41-09 > E-Mail : sebastian.hu...@embedded-brains.de > PGP : Public key available on request. > > Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG. > _______________________________________________ > rtems-devel mailing list > rtems-devel@rtems.org > http://www.rtems.org/mailman/listinfo/rtems-devel _______________________________________________ rtems-devel mailing list rtems-devel@rtems.org http://www.rtems.org/mailman/listinfo/rtems-devel
