From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5245EC43387 for ; Tue, 18 Dec 2018 00:08:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1BDB1214C6 for ; Tue, 18 Dec 2018 00:08:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726360AbeLRAIB (ORCPT ); Mon, 17 Dec 2018 19:08:01 -0500 Received: from mga06.intel.com ([134.134.136.31]:30032 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726271AbeLRAIB (ORCPT ); Mon, 17 Dec 2018 19:08:01 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Dec 2018 16:08:00 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,366,1539673200"; d="scan'208";a="99489609" Received: from tassilo.jf.intel.com (HELO tassilo.localdomain) ([10.7.201.137]) by orsmga007.jf.intel.com with ESMTP; 17 Dec 2018 16:08:00 -0800 Received: by tassilo.localdomain (Postfix, from userid 1000) id 9A836300B49; Mon, 17 Dec 2018 16:08:00 -0800 (PST) Date: Mon, 17 Dec 2018 16:08:00 -0800 From: Andi Kleen To: Peter Zijlstra Cc: Arnd Bergmann , Nicolas Pitre , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Paul McKenney , Will Deacon , Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH 0/7] ARM: hacks for link-time optimization Message-ID: <20181218000800.GB25620@tassilo.jf.intel.com> References: <20180220215954.4092811-1-arnd@arndb.de> <20181217225020.GA16520@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181217225020.GA16520@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 17, 2018 at 11:50:20PM +0100, Peter Zijlstra wrote: > On Tue, Feb 20, 2018 at 10:59:47PM +0100, Arnd Bergmann wrote: > > Hi Nico, all, > > > > I was playing with ARM link-time optimization handling earlier this > > month, and eventually got it to build cleanly with randconfig kernels, > > but ended up with a lot of ugly hacks to actually pull it off. > > How are we dealing with the fact that LTO can break RCU in very subtle > and scary ways? > > Do we have a compiler guy on board that has given us a compiler switch > that kills that optimization (and thereby guarantees that behaviour for > future compilers etc..) ? Can you actually define what optimization you are worred about? If there are optimizations that cause problems they likely happen even without LTO inside files. The only difference with LTO is that it does them between files too. -Andi