Messages in this thread | | | From | David Howells <> | Subject | Re: start_kernel(): bug: interrupts were enabled early | Date | Fri, 02 Apr 2010 15:46:14 +0100 |
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Linus Torvalds <torvalds@linux-foundation.org> 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
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