From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932315AbbDHNxv (ORCPT ); Wed, 8 Apr 2015 09:53:51 -0400 Received: from mail-ig0-f181.google.com ([209.85.213.181]:37998 "EHLO mail-ig0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754523AbbDHNxl (ORCPT ); Wed, 8 Apr 2015 09:53:41 -0400 Message-ID: <552532DF.7060004@gmail.com> Date: Wed, 08 Apr 2015 09:53:35 -0400 From: Austin S Hemmelgarn User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Pengfei Yuan <0xcoolypf@gmail.com> CC: Mike Galbraith , linux-kernel@vger.kernel.org Subject: Re: Why not build kernel with -O3 References: <1428388995.3152.10.camel@gmail.com> <1428401356.3152.38.camel@gmail.com> <55241C51.8040107@gmail.com> <552519AF.1060201@gmail.com> In-Reply-To: x-hashcash: 1:21:150408:0xcoolypf@gmail.com::5f985701537a1a4735dba109cd40452:e5eefbccc89d074d x-hashcash: 1:21:150408:umgwanakikbuti@gmail.com::eb92a1f9061172179ebe7904e5f9e7fa:8fd24bc361e0b14c x-hashcash: 1:21:150408:linux-kernel@vger.kernel.org::3db1993ca873316afa7f500e6e045b0:ecef67c0a2ee15a7 x-stampprotocols: hashcash:1:17;mbound:0:10:3000:5000 Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary="------------ms020504070704030506010302" X-Antivirus: avast! (VPS 150408-1, 2015-04-08), Outbound message X-Antivirus-Status: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a cryptographically signed message in MIME format. --------------ms020504070704030506010302 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-04-08 09:19, Pengfei Yuan wrote: > 2015-04-08 20:06 GMT+08:00 Austin S Hemmelgarn : >> I can't remember any off the top of my head, but it does say explicitl= y in >> the GCC manual to be careful with -O3. IIRC, most of the issues relat= e to >> -O3 enabling -ffast-math (which tends to really mess with code that ex= pects >> strict IEEE 754 compliance), so it may not be as much of an issue for = kernel >> code. You might look into some of the projects that use -O3 by defaul= t (I >> think most of the Mozilla so0ftware does these days, and I know that t= here >> are others, I just can't remember what right now). >> > > I am afraid you are talking about -Ofast, not -O3. > See https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html > > Yuan > You're right, I had been looking at the wrong paragraph in the info=20 manual. 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