Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753945AbaK0M0m (ORCPT ); Thu, 27 Nov 2014 07:26:42 -0500 Received: from mx0.aculab.com ([213.249.233.131]:38909 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751512AbaK0M0l convert rfc822-to-8bit (ORCPT ); Thu, 27 Nov 2014 07:26:41 -0500 From: David Laight To: "'Joe Perches'" , Alexei Starovoitov CC: Quentin Lambert , "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , "Patrick McHardy" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return Thread-Topic: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return Thread-Index: AQHQCbS8Fl/IWugLR0q7Tb6zBSGc/Zx0Zp1A Date: Thu, 27 Nov 2014 12:25:25 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1C9FDA63@AcuExch.aculab.com> References: <1417032059.16355.4.camel@perches.com> In-Reply-To: <1417032059.16355.4.camel@perches.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Joe Perches > On Wed, 2014-11-26 at 10:34 -0800, Alexei Starovoitov wrote: > > On Wed, Nov 26, 2014 at 10:02 AM, Joe Perches wrote: > > > On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote: > > >> On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches wrote: > > > > > >> > Is there any value in reordering these tests for frequency > > >> > or maybe using | instead of || to avoid multiple jumps? > > >> > > >> probably not. It's not a critical path. > > >> compiler may fuse conditions depending on values anyway. > > >> If it was a critical path, we could have used > > >> (1 << reg) & mask trick. > > >> I picked explicit 'return true' else 'return false' here, > > >> because it felt easier to read. Just a matter of taste. > > > > > > There is a size difference though: (allyesconfig) > > > > > > $ size arch/x86/net/built-in.o* > > > text data bss dec hex filename > > > 12999 1012 4336 18347 47ab arch/x86/net/built-in.o.new > > > 13177 1076 4592 18845 499d arch/x86/net/built-in.o.old > > > > interesting. Compiler obviously thinks that 178 byte increase > > with -O2 is the right trade off. Which I agree with :) > > > > If I think dropping 'inline' and using -Os will give bigger savings... > > This was allyesconfig which already uses -Os > > Using -O2, there is no difference using inline > or not, but the size delta with the bitmask is > much larger > > $ size arch/x86/net/built-in.o* (allyesconfig, but not -Os) > text data bss dec hex filename > 13410 820 3624 17854 45be arch/x86/net/built-in.o.new > 16130 884 4200 21214 52de arch/x86/net/built-in.o.old > 16130 884 4200 21214 52de arch/x86/net/built-in.o.static That is quite a big % change in the code size. Why the change in data? David -- 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/