Re: [PATCH] x86: percpu_to_op() misses memory and flags clobbers

[Jeremy Fitzhardinge]

Herbert Xu wrote:
> Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
>   
> > There's probably not a lot of value in this.  The Intel and AMD 
> > optimisation guides tend to deprecate inc/dec in favour of using 
> > add/sub, because the former can cause pipeline stalls due to its partial 
> > flags update.
> >     
>
> Is this still the case on the latest Intel CPUs?
>   

Yes:

   Assembly/Compiler Coding Rule 32. (M impact, H generality) INC and DEC
   instructions should be replaced with ADD or SUB instructions,
   because ADD and
   SUB overwrite all flags, whereas INC and DEC do not, therefore
   creating false
   dependencies on earlier instructions that set the flags.

   J
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