From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261875AbTJWXXl (ORCPT ); Thu, 23 Oct 2003 19:23:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261877AbTJWXXl (ORCPT ); Thu, 23 Oct 2003 19:23:41 -0400 Received: from mail-03.iinet.net.au ([203.59.3.35]:52413 "HELO mail.iinet.net.au") by vger.kernel.org with SMTP id S261875AbTJWXXi (ORCPT ); Thu, 23 Oct 2003 19:23:38 -0400 Message-ID: <3F986311.40804@cyberone.com.au> Date: Fri, 24 Oct 2003 09:24:01 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030827 Debian/1.4-3 X-Accept-Language: en MIME-Version: 1.0 To: "J.A. Magallon" CC: "Joseph D. Wagner" , linux-kernel@vger.kernel.org Subject: Re: FEATURE REQUEST: Specific Processor Optimizations on x86 Architecture References: <200310221855.15925.theman@josephdwagner.info> <20031023230542.GC2084@werewolf.able.es> In-Reply-To: <20031023230542.GC2084@werewolf.able.es> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org J.A. Magallon wrote: >On 10.22, Joseph D. Wagner wrote: > >>Yes, I know you can select Pentium III, Pentium 4, Athlon, etc, under >>processor type when doing a 'make xconfig', but those selections do not >>translate into the appropriate -mcpu and -march flags. >> >>While the kernel on x86 architecture can be optimized in terms of generic >>processor specifications (i.e. i386, i486, i586, i686), the kernel can't be >>optimized beyond a i686. >> >>If you select Pentium III, the -march flag is set to i686. >>If you select Pentium 4, the -march flag is set to i686. >>If you select Athlon 4, the -march flag is set to i686. >>If you select Athlon XP, the -march flag is set to i686. >> >>It should be that... >> >>If you select Pentium III, the -march flag is set to pentium3. >>If you select Pentium 4, the -march flag is set to pentium4. >>If you select Athlon 4, the -march flag is set to athlon-4. >>If you select Athlon XP, the -march flag is set to athlon-xp. >> >>I don't want to have to hand edit the makefiles just to optimize my kernel. >>I think this change is simple enough to do, and would allow kernel >>developers the option of processor-specific optimizations in the future. >> >>TIA. >> >>Joseph D. Wagner >> > >I have sent the attached patches sometimes to the list/Marcelo, and they >have been rejected to the moment because: >- gcc can spit some new instructions, reorganize code and other things when > you jump from i686 to pentium3, for example. >- There can be bugs both in gcc and in the kernel that can be triggered by > >i686 optimizations/code. >- This is not safe for a stable kernel, it was done in 2.5, bugs appeared, > were corrected, and so on, 'cause this was a development kernel. > Not that I think this should go in anyway, but the only way you ever might get it in is if you measure significant performance improvements. I don't think you will.