Re: [git pull] x86 fixes

From: Arjan van de Ven
Date: Mon Sep 08 2008 - 15:55:49 EST

On Mon, 8 Sep 2008 12:30:02 -0700 (PDT)
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> 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.

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

makes sense

> - "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)

> 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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