From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261159AbVGTKie (ORCPT ); Wed, 20 Jul 2005 06:38:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261151AbVGTKib (ORCPT ); Wed, 20 Jul 2005 06:38:31 -0400 Received: from 167.imtp.Ilyichevsk.Odessa.UA ([195.66.192.167]:701 "HELO port.imtp.ilyichevsk.odessa.ua") by vger.kernel.org with SMTP id S261152AbVGTKia (ORCPT ); Wed, 20 Jul 2005 06:38:30 -0400 From: Denis Vlasenko To: ivan@yosifov.net, Kerin Millar Subject: Re: Noob question. Why is the for-pentium4 kernel built =?koi8-r?q?with=09-march=3Di686?= ? Date: Wed, 20 Jul 2005 13:38:08 +0300 User-Agent: KMail/1.5.4 Cc: linux-kernel@vger.kernel.org References: <1121792852.11857.6.camel@home.yosifov.net> <1121852642.18129.39.camel@localhost> <1121851507.10454.3.camel@home.yosifov.net> In-Reply-To: <1121851507.10454.3.camel@home.yosifov.net> MIME-Version: 1.0 Content-Type: text/plain; charset="koi8-r" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200507201338.08179.vda@ilport.com.ua> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 20 July 2005 12:25, Ivan Yosifov wrote: > > > > Also, I believe that the -march=pentium4 option /was/ actually used up > > > > until kernel 2.6.10 where it was dropped because of a risk that some > > > > versions of gcc would cause the kernel to use SSE registers for data > > > > movement (which is a no-no). > > > > > > > > > > You seem right. I fetched a 2.6.9 tarball and it is really built with > > > -march=pentium4. Do you know which are versions of gcc in question ? > > > > > > > No, I'm afraid not. I only know that the advice came from Richard > > Henderson who (I think) is one of the core glibc hackers. You can see > > the point at which it was introduced by Linus in the ChangeLog (2nd > > message from last): > > > > http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.10 > > Seems to be this one: > > > Don't use "-march=pentium3" for gcc tuning. > > rth tells me that some versions of gcc may end up using the > SSE registers for data movement when you do that. > > Use "-march=i686 -mtune=xxxx" instead. > > (We do the same thing for march=pentium2/4 too, just for > consistency). > > > The way it is worded it seems that it is a problem with *some* versions > of gcc only on p3, not p4. Why do you care? I bet that differences between i686 code and pentium4 code are well below noise level. -- vda