From: Kyle McMartin <kyle@xxxxxxxxxxxxxxxx> Date: Sun, 27 May 2007 23:11:14 -0400 > Yeah, David Howells wanted to use cmpxchg in his work struct patch, but > had to not because not everyone implements it. > > >From what I can tell, very few arches actually have CAS, and others > emulate it with LL/SC type implementations. That's fine, as a LL/SC implementation of cmpxchg() is fully atomic and would work in concert with a userspace cmpxchg() implemented with LL/SC. It's the platforms that lack CAS _and_ some kind of LL/SC which are problematic. Sparc32 SMP cpus (sparcv8 sun4m and later) have a 'swap' instruction but that does not have an inifinite consensus number like CAS and LL/SC, so it can't be used to implement cmpxchg() (and also the non-SMP sparc32 chips lack the instruction). - To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
