linux-kernel - Re: [RFC, Announce] Unified x86 architecture, arch/x86

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Message-Id: <200707210737.59552.ak@suse.de>
Date:	Sat, 21 Jul 2007 07:37:58 +0200
From:	Andi Kleen <ak@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC, Announce] Unified x86 architecture, arch/x86

On Saturday 21 July 2007 00:32, Thomas Gleixner wrote:
> We are pleased to announce a project we've been working on for some
> time: the unified x86 architecture tree, or "arch/x86" - and we'd like
> to solicit feedback about it.

Well you know my position on this. I think it's a bad idea because
it means we can never get rid of any old junk. IMNSHO arch/x86_64
is significantly cleaner and simpler in many ways than arch/i386 and I would
like to preserve that. Also in general arch/x86_64 is much easier to hack
than arch/i386 because it's easier to regression test and in general
has to care about much less junk. And I don't 
know of any way to ever fix that for i386 besides splitting the old
stuff off completely.

Besides radical file movements like this are bad anyways. They cause
a big break in patchkits and forward/backwards porting that doesn't 
really help anybody.

> This causes double maintenance
> even for functionality that is conceptually the same for the 32-bit and
> the 64-bit tree. (such as support for standard PC platform architecture
> devices)

It's not really the same platform: one is PC hardware going back forever
with zillions of bugs, the other is modern PC platforms which much less
bugs and quirks

To see it otherwise it's more a junkification of arch/x86_64 than
a cleanup of arch/i386 -- in fact you didn't really clean up arch/i386 
at all.

> How did we do it?
> -----------------
>
> As an initial matter, we made it painstakingly sure that the resulting
> .o files in a 32-bit build are bit for bit equal.

You got not a single line less code duplication then, so i don't really
see the point of this.

-Andi
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