On Mon, 8 Sep 2008 12:30:02 -0700 (PDT)
Linus Torvalds <torvalds@linux-foundation.org> wrote:
quoted text
> 
> I think there are realistically three classes:
> 
>  - _really_ old, to the point of being totally useless for SMP.
> 
>    This is really just 386 and clones. We _need_ a working WP for a 
>    race-free access_ok(), and we need cmpxchg (and lately xadd).
> 
>    Smaller pains even on UP: bswap doesn't exist. invlpg doesn't
> exist. 

I'd lump all cpus that don't have cpuid in this bucket too (eg half the
486es) simply because not having cpuid is painful in pretty much the
same way.

quoted text
>  - old. pre-cmov. i486 and pentium, and some clones.

makes sense
 
quoted text
>  - "modern 32-bit": PPro and better. Can take CMOV, MMX and TSC for 
>    granted.

again makes sense; question is if it makes sense to take PSE and PAE
for granted as well (although PSE we can do runtime I suppose)

quoted text
> Hmm? Doesn't that sound like a sane model?

it does to me; the only question is if we hit a new bucket with the
various fancy string instructions that are in upcoming models; doing
string/copy operations inlined for those guys will make a fourth bucket.


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