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Message-ID: <20090115141734.GA15732@elte.hu>
Date: Thu, 15 Jan 2009 15:17:34 +0100
From: Ingo Molnar <mingo@...e.hu>
To: "Maciej W. Rozycki" <macro@...ux-mips.org>
Cc: 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 ...
Ingo
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