From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937636AbXGLAh3 (ORCPT ); Wed, 11 Jul 2007 20:37:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755929AbXGLAhR (ORCPT ); Wed, 11 Jul 2007 20:37:17 -0400 Received: from one.firstfloor.org ([213.235.205.2]:50571 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756469AbXGLAhQ (ORCPT ); Wed, 11 Jul 2007 20:37:16 -0400 Date: Thu, 12 Jul 2007 02:37:13 +0200 From: Andi Kleen To: Ingo Molnar Cc: Andi Kleen , Linus Torvalds , Thomas Gleixner , Andrew Morton , linux-kernel@vger.kernel.org, Arjan van de Ven , Chris Wright Subject: Re: x86 status was Re: -mm merge plans for 2.6.23 Message-ID: <20070712003713.GB26585@one.firstfloor.org> References: <20070711174252.GA16793@elte.hu> <1184191488.12353.160.camel@chaos> <1184194219.12353.170.camel@chaos> <20070711233618.GD25510@one.firstfloor.org> <20070711235852.GA625@elte.hu> <20070712000720.GA26585@one.firstfloor.org> <20070712001807.GB1946@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070712001807.GB1946@elte.hu> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 12, 2007 at 02:18:07AM +0200, Ingo Molnar wrote: > > > i dont think "clean, modern x86 code" will ever happen - x86_64 has > > > and is going to have the exact same type of crap. And i'll say a > > > weird thing > > > > Yes, but it will be new crap, but no old crap anymore. > > > > If you always pile the new crap on the old crap at some point the > > whole thing might fall over. 64bit was intended as a fresh start. > > I think there's no such thing as a fresh start for a diverse > architecture - the ia64 failure has proven that. x86_64 CPUs still do > A20 emulation today (!). x86-64 doesn't care about a lot of x86 baggage and a lot of things have been even obsoleted in the platform. In practice the backwards compatibility on x86 isn't that great either. For example a significant number of new systems don't even work correctly in PIC mode anymore. > We still have people running industrial boards > on real i386 DX CPUs, with the latest upstream kernel. 15 years ago an Yes, but those for example would be perfectly happy with an arch/i386 with all APIC and SMP code stripped out. Only the few people who still run dual P5s might not, but those could continue using old kernels. But eventually I think that would be the right clean way: arch/i386 stripped down port for truly old systems like the embedded 386 upto 586 or early 686. No SMP or APIC. arch/x86 supporting 32bit and 64bit for reasonably modern systems. NUMAQ/Voyager/P5-SMP/visual workstation gone [frankly the user base of those is too small to justify the code impact] It's just quite ugly to get there and when you think through it the actual advantages of such a setup it is likely not enough to justify the significant work to make it work. Also I wouldn't have any idea how to regression test significant changes to arch/i386 aimed at old systems. e.g. I don't think the powerpc people actually tried to still support really old systems where it is hard to do regression tests anymore, only really supported platforms. So while such a setup would be quite nice the practical problems of getting there are nasty. Also I must admit I prefer hacking on new code instead. -Andi