Messages in this thread | | | Date | Wed, 14 Jul 2010 16:22:52 -0700 | Subject | Re: [patch 1/2] x86_64 page fault NMI-safe | From | Linus Torvalds <> |
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On Wed, Jul 14, 2010 at 4:09 PM, Andi Kleen <andi@firstfloor.org> wrote: > > It can happen in theory, but for such a rare case take a lock > and walking everything should be fine.
Actually, that's _exactly_ the wrong kind of thinking.
Bad latency is bad latency, even when it happens rarely. So latency problems kill - even when they are rare. So you want to avoid them. And walking every possible page table is a _huge_ latency problem when it happens.
In contrast, what's the advantage of doing thigns synchronously while holding a lock? It's that you can avoid a few page faults, and get better CPU use. But that's _stupid_ if it's something that is very rare to begin with.
So the very rarity argues for the lazy approach. If it wasn't rare, there would be a much stronger argument for trying to do things up-front.
Linus
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