Re: [PATCH 3/4] Pte xchg optimization.patch

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Dave Jones wrote:
On Wed, Apr 11, 2007 at 10:30:58PM -0700, Zachary Amsden wrote:
 > In situations where page table updates need only be made locally, and there
 > is no cross-processor A/D bit races involved, we need not use the heavyweight
 > xchg instruction to atomically fetch and clear page table entries.  Instead,
 > we can just read and clear them directly.
> > This introduces a neat optimization for non-SMP kernels; drop the atomic
 > xchg operations from page table updates.

Would it be feasible to do this using the smp_alternatives stuff?
Given many distros are now shipping SMP-only kernels, it'd be nice
to get that win without using having to rebuild their kernels.

That's a good point. It is a fairly straightforward substitution for the static case:

xchg reg, mem

to

mov mem, reg
mov imm, mem

I'll give it a spin and see how it drives. It is, though, less obvious how easy it will be for PAE kernels.

Zach
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