Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > Ahh, yes. In this case, that doesn't likely change anything. The > save/restore versions of the irq-safe locks shouldn't be appreciably more > expensive than the non-saving ones. And architectures that really care > should have done their own per-arch optimized version anyway. That depends on the CPU. Some CPUs have quite expensive interrupt disablement instructions. FRV does for instance; but fortunately, on the FRV, I can use some of the excessive quantities of conditional registers to pretend that I disable interrupts, and only actually do so if an interrupt actually happens. > Maybe we should even document that - so that nobody else makes the mistake > x86-64 did of thinking that the "generic spinlock" version of the rwsem's > is anything but a hacky and bad fallback case. In some cases, it's actually the best way. On a UP machine, for instance, where they reduce to nothing or where your only atomic instruction is an XCHG equivalent. David -- 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
