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

[Zachary Amsden <zach@vmware.com>]

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