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SubjectRe: Is 386 processor still supported?

* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> > > Hmm. Where in Kconfig is SMP for M386 not allowed?
> >
> > Dunno, kconfig is too much of a jungle for a simple person like me ;-)
> >
> > But afaik i386 (and possibly i486) don't support nearly enough for a
> > modern SMP system.
> >
> > Alan used to have i486-smp I think, one of the very few ever made.
>
> The first systems that supported the Intel MP standard are 486 based
> with external APIC. The prior systems used various proprietary MP
> interfaces from the simple stuff in the Compaq (which Linux doesn't
> support as Compaq refused to allow Thomas Radke to contribute it) to the
> fairly extreme end of things with the Sequent boxes.
>
> In addition our FPU emulation and some of our handling for x86
> processors where we have to do the WP bit in software is also not SMP
> safe.
>
> So our minimal spec for SMP is probably 486DX + external Intel APIC.
>
> In practice I doubt there is a single Intel APIC type 486 SMP box on the
> planet running Linux (or quite possibly running at all)

yeah, that's very likely true. I think we could eliminate some of the SMP
complications by requiring cmpxchg presence for CONFIG_SMP, agreed?

Ingo


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