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

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Message-ID: <20090116090002.GD4795@atrey.karlin.mff.cuni.cz>
Date:	Fri, 16 Jan 2009 10:00:02 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jan-Benedict Glaw <jbglaw@...-owl.de>,
	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?

> 
> * Maciej W. Rozycki <macro@...ux-mips.org> wrote:
> 
> > On Thu, 15 Jan 2009, Alan Cox wrote:
> > 
> > > >  UP emulation of CMPXCHG and XADD for userland should be rather trivial, 
> > > > so why not include it like with LL/SC for MIPS?
> > > 
> > > Why not just ship an additional libc with the right options ?
> > 
> >  Does not work for MIPS as glibc has no equivalent code for pre-LL/SC 
> > CPUs and LL/SC is always used.  For the i386 the situation seems worse 
> > yet as for pre-i486 CPUs a generic C implementation of 
> > compare-and-exchange is used guaranteeing silent thread unsafety. :(
> > 
> >  IMO, a kernel emulation of CMPXCHG and XADD (both are used by 
> > sysdeps/i386/i486/bits/atomic.h in glibc) with an optional LOCK prefix, 
> > guaranteeing UP atomicity would be a cheap way to provide long-term i386 
> > userland support with little burden for both Linux and respective user 
> > software maintainers.  Certainly it adds some bloat to the kernel, but I 
> > think it is not an option that should be outright dismissed without 
> > consideration.
> 
> patches are welcome ...

Hehe, I guess the only long-term solution is to get shiny old 386 as a
part of Ingo's test farm ;-).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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