Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755358AbbDKOlk (ORCPT ); Sat, 11 Apr 2015 10:41:40 -0400 Received: from ud10.udmedia.de ([194.117.254.50]:46890 "EHLO mail.ud10.udmedia.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752896AbbDKOli (ORCPT ); Sat, 11 Apr 2015 10:41:38 -0400 Date: Sat, 11 Apr 2015 16:41:35 +0200 From: Markus Trippelsdorf To: "H. Peter Anvin" Cc: Denys Vlasenko , Ingo Molnar , "Paul E. McKenney" , Linus Torvalds , Jason Low , Peter Zijlstra , Davidlohr Bueso , Tim Chen , Aswin Chandramouleeswaran , LKML , Borislav Petkov , Andy Lutomirski , Brian Gerst , Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH] x86: Align jump targets to 1 byte boundaries Message-ID: <20150411144135.GB31416@x4> References: <20150409183926.GM6464@linux.vnet.ibm.com> <20150410090051.GA28549@gmail.com> <20150410091252.GA27630@gmail.com> <20150410092152.GA21332@gmail.com> <20150410111427.GA30477@gmail.com> <20150410112748.GB30477@gmail.com> <20150410120846.GA17101@gmail.com> <5527C700.3030405@redhat.com> <5527CD92.1080901@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5527CD92.1080901@zytor.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 983 Lines: 25 On 2015.04.10 at 06:18 -0700, H. Peter Anvin wrote: > On 04/10/2015 05:50 AM, Denys Vlasenko wrote: > > > > However, I'm an -Os guy. Expect -O2 people to disagree :) > > > > The problem with -Os is that the compiler will make *any* tradeoffs to > save a byte. It is really designed to squeeze as much code into a > fixed-size chunk, e.g. a ROM, as possible. > > We have asked for an -Okernel mode from the gcc folks forever. It > basically would mean "-Os except when really dumb." If you want the best of both worlds perhaps you should reconsider Andy's LTO patch? With -flto gcc automatically optimizes all functions that it considers cold for size. So you could expect some code size savings even with -O2 (or -O3). -- Markus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/