Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752453AbaKZUBG (ORCPT ); Wed, 26 Nov 2014 15:01:06 -0500 Received: from smtprelay0051.hostedemail.com ([216.40.44.51]:56617 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750770AbaKZUBF (ORCPT ); Wed, 26 Nov 2014 15:01:05 -0500 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2198:2199:2393:2553:2559:2562:2693:2828:3138:3139:3140:3141:3142:3353:3622:3653:3865:3866:3867:3868:3870:3871:3872:3874:4321:5007:6119:6261:6742:7903:7974:8531:8603:10004:10400:10848:11232:11658:11914:12043:12517:12519:12555:12740:13069:13146:13230:13311:13357:14096:14097:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: fact17_8da215424803 X-Filterd-Recvd-Size: 3015 Message-ID: <1417032059.16355.4.camel@perches.com> Subject: Re: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return From: Joe Perches To: 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" Date: Wed, 26 Nov 2014 12:00:59 -0800 In-Reply-To: References: Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.12.7-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 -- 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/