On Mon, 2010-08-23 at 15:44 +0200, Arnd Bergmann wrote: > > * Alpha has an optimization for the uniprocessor case, where the atomic > instructions get turned into nonatomic additions. The spinlock based > version uses no locks on UP but disables interrupts for reasons I don't > understand (nothing running at interrupt time should try to access an rwsem). > Should the generic version do the same as Alpha? I've seen drivers in the past do trylocks at interrupt time ... tho I agree it sucks. > * Is there any architecture that would still benefit from having a separate > rwsem implementation? AFAICT all the remaining ones are just variations of > the same concept of using cmpxchg (or xadd in case of x86), which is what > atomics typically end up doing anyway. It depends how sensitive rwsems are. The "generic" variant based on atomic's and cmpxchg on powerpc is sub-optimal in the sense that it has stronger memory barriers that would be necessary (atomic_inc_return for example has both acquire and release). But that vs. one more pile of inline asm, we decided it wasn't hot enough a spot for us to care back then. Cheers, Ben. -- 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
