Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752574AbbFXMVC (ORCPT ); Wed, 24 Jun 2015 08:21:02 -0400 Received: from smtprelay.synopsys.com ([198.182.47.9]:53898 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751796AbbFXMUy (ORCPT ); Wed, 24 Jun 2015 08:20:54 -0400 Message-ID: <558AA080.7070801@synopsys.com> Date: Wed, 24 Jun 2015 17:50:16 +0530 From: Vineet Gupta User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 Newsgroups: gmane.linux.kernel.cross-arch,gmane.linux.kernel To: Michal Marek , Geert Uytterhoeven CC: "linux-arch@vger.kernel.org" , lkml Subject: Re: subtle side effect of commit a1c48bb160f836 References: <55826966.6050202@synopsys.com> <20150618081329.GA9434@pobox.suse.cz> <55828527.8050901@synopsys.com> <55829A0B.8070804@suse.cz> <55829E51.3060007@synopsys.com> In-Reply-To: <55829E51.3060007@synopsys.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.12.197.3] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3228 Lines: 79 Hi Michal, On Thursday 18 June 2015 04:02 PM, Vineet Gupta wrote: > On Thursday 18 June 2015 03:44 PM, Michal Marek wrote: >> Dne 18.6.2015 v 10:45 Vineet Gupta napsal(a): >>>> On Thursday 18 June 2015 01:43 PM, Michal Marek wrote: >>>>>>>>>> Alternatively, as we already have CONFIG_CC_OPTIMIZE_FOR_SIZE, >>>>>>>>>> a(nother) Kconfig option may make sense. >>>>>> We can also introduce some ARCH_CFLAGS that is appended near the end of >>>>>> the list, and have arc/Makefile add its -O3 there. But I'd like to why >>>>>> the -O3 needs to be there in first place. >>>> >>>> This is how historically ARC kernels have been built. We do track performance >>>> results LMBench/hackbench... and going from -O3 to -O2 caused a sudden dip in some >>>> of the numbers when we measured 3.18 (vs. 3.13) >>>> >>>>>> Obviously, the kernel works >>>>>> with -O2, otherwise the regression would have been identified earlier. >>>> >>>> Its a performance thing - so yeah -O2 works, but -O3 works even better :-) >>>> >>>>>> So why can't users specify -O3 in KCFLAGS like on any other >>>>>> architecture. >>>> >>>> Sweet, I didn't know about this. But I don't see any arch setting this - only tile >>>> using it. So yeah - below does the trick ! >>>> >>>> ---------> >>>> From 5e44cd2ed69b1d030b4cb87600d2767b69c35537 Mon Sep 17 00:00:00 2001 >>>> From: Vineet Gupta >>>> Date: Thu, 18 Jun 2015 13:54:01 +0530 >>>> Subject: [PATCH] ARC: Override toplevel default -O2 with -O3 >>>> >>>> ARC kernels have historically been built with -O3, despite top level >>>> Makefile defaulting to -O2. This was facilitated by implicitly ordering >>>> of arch makefile include AFTER top level assigned -O2. >>>> >>>> An upstream fix to top level a1c48bb160f ("Makefile: Fix unrecognized >>>> cross-compiler command line options") changed the ordering, making ARC >>>> -O3 defunt. >>>> >>>> Fix that by NOT relying on any ordering whatsoever and use the right >>>> mechanism to do the over-rides. >>>> >>>> Suggested-by: Michal Marek >>>> Cc: Geert Uytterhoeven >>>> Cc: >>>> Signed-off-by: Vineet Gupta >>>> --- >>>> arch/arc/Makefile | 1 + >>>> 1 file changed, 1 insertion(+) >>>> >>>> diff --git a/arch/arc/Makefile b/arch/arc/Makefile >>>> index 86c71b2089d2..c23f3f2b0ff8 100644 >>>> --- a/arch/arc/Makefile >>>> +++ b/arch/arc/Makefile >>>> @@ -44,6 +44,7 @@ endif >>>> ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE >>>> # Generic build system uses -O2, we want -O3 >>>> cflags-y += -O3 >>>> +KCFLAGS += -O3 >>>> endif >> Uh, this is not what I meant. KCFLAGS is a *user* setting. It's meant to >> be set in the environment or command line. > > Well I don't want to rely on external settings whatsoever to enforce this. If this > is not the right way, what do u suggest I do to help fix this. Can I keep this seeming abuse of KCFLAGS or do u suggest alternate approach I can code up ! Thx, -Vineet -- 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/