On 09/10/2013 09:24 AM, Linus Torvalds wrote:
> On Tue, Sep 10, 2013 at 8:29 AM, Arjan van de Ven <ar...@linux.intel.com>
> wrote:
>>>
>> also.. yuck on using "dec"
>> "dec" sucks, please use "sub foo ,1" instead
>
> That's a bigger instruction, largely due to the constant.
>
>> (dec sucks because of its broken flags behavior; it creates basically a
>> bubble in the pipeline)
>
> Intel could (and should) just fix that. It's "easy" enough - you just
> need to rename the carry flag as a separate register (and make sure
> that the conditional instructions that don't use it don't think they
> need it).
>
> In fact I thought Intel already did that on their large cores. Are you
> sure they still have trouble with inc/dec?
>
Big cores are fine, but Atom (and presumably Quark) might still suffer a
performance penalty.
-hpa
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