On Wed, 21 Dec 2011, Tejun Heo wrote: > The thing is that irqsafe ones are the "complete" ones. We can use > irqsafe ones instead of preempt safe ones but not the other way. This > matters only if flipping irq is noticeably more expensive than > inc/dec'ing preempt count but I suspect there are enough such > machines. (cc'ing arch) Does anyone have better insight here? How > much more expensive are local irq save/restore compared to inc/dec'ing > preempt count on various archs? Well that would be a pretty nice simplification of the API. Replace the fallback code for the preempt safe ones with the irqsafe fallbacks, then drop the irqsafe variants from percpu.h. > > The way that the cmpxchg things are used is also similar to transactional > > memory that is becoming available in the next generation of processors by > > Intel and that is already available in the current generation of powerpc > > processors by IBM. It is a way to avoid locking overhead. > > Hmmm... how about removing the ones which aren't currently in use? Yep. Could easily be done. We can resurrect the stuff as needed when other variants become necessary. In particular the _and and _or etc stuff was just added to be backward compatible with the old per cpu and local_t interfaces. There may be no use cases left. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
