From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755030Ab2GKF33 (ORCPT ); Wed, 11 Jul 2012 01:29:29 -0400 Received: from ozlabs.org ([203.10.76.45]:57468 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751512Ab2GKF32 (ORCPT ); Wed, 11 Jul 2012 01:29:28 -0400 From: Rusty Russell To: Arnd Bergmann , Alan Cox Cc: Catalin Marinas , Ingo Molnar , Olof Johansson , "linux-kernel\@vger.kernel.org" , Linus Torvalds , Russell King , Andrew Morton Subject: Re: [PATCH 00/36] AArch64 Linux kernel port In-Reply-To: <201207101652.18401.arnd@arndb.de> References: <1341608777-12982-1-git-send-email-catalin.marinas@arm.com> <20120710101018.GE15120@arm.com> <20120710163358.6ae4a576@pyramind.ukuu.org.uk> <201207101652.18401.arnd@arndb.de> User-Agent: Notmuch/0.12 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) Date: Wed, 11 Jul 2012 14:56:49 +0930 Message-ID: <877guarhpi.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 10 Jul 2012 16:52:18 +0000, Arnd Bergmann wrote: > On Tuesday 10 July 2012, Alan Cox wrote: > > > In the AArch32 kernel port many implementation decisions newer > > > architectures were made in a way that preserves backwards compatibility > > > to over 15 years ago (and for good reasons, ARMv4 hardware is still in > > > use). But keeping the same decisions in AArch64 is wrong. > > > > Same argument as x86-32 v x86-64. Same issues about compatibility. > > Similar but not the same. In case of x86-64 the hardware was actually > meant to run old 32 bit kernel binaries and still can. I don't I know it's a crazy idea, but why don't we try some actual analysis? In 2.5.5, when arch/x86_64 was introduced it was 35412 lines of code. hashmatch (http://www.samba.org/~tridge/hashmatch) says that about 24642 are identical with arch/i386 in the same kernel. That's 70%. Some of that's boilerplate: 9610 lines are in common with arch/sparc64 (27%), so let's say that 43% of x86-64 was specifically sharable with i386. arch/aarch64/ is 22016 line of code. Hashmatch says 12509 (57%) is in common with arch/arm. But only 3232 lines (15%) are in common with sparc. So let's say that 42% of aarch64 is specifically sharable with arm. Looks equivalent to me. They will merge eventually. That said: 1) It's nice to have a clear division of maintainer responsibilities in the near term. 2) PowerPC only "merged" by removing a raft of older platforms, and I don't think ARM is ready for that. And yes, aarch64 is a stupid name. Cheers, Rusty.