linux-kernel - Re: Is 386 processor still supported?

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Date:	Thu, 8 Jan 2009 16:10:46 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Jiri Kosina <jkosina@...e.cz>, Adam Osuchowski <adwol@...k.pl>,
	linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Is 386 processor still supported?


* Alan Cox <alan@...rguk.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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