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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 8B3FAC433E0 for ; Wed, 1 Jul 2020 16:03:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C5F620780 for ; Wed, 1 Jul 2020 16:03:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593619423; bh=lsVbSj/ss2har/B90Io45Cd2wBUKELeZ+wmjiYF4Efg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=ciw985aZ37gP7kSOqrMaDA+hd4gbsAmb02Fw0nM+bmuu+weeZp2jwHVh1ip7CvS/g h7Ituy28ywHdo5rl3m11R7Ak8ScomPcmxoA3I9jgQGE7XDdud8a1uREdACLelpUfIy ABR/3SskVfgTqCSNxvzDG60wqt4LvgHo/4quuMr8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732321AbgGAQDl (ORCPT ); Wed, 1 Jul 2020 12:03:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:40324 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731672AbgGAQDi (ORCPT ); Wed, 1 Jul 2020 12:03:38 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 776DA206C3; Wed, 1 Jul 2020 16:03:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593619418; bh=lsVbSj/ss2har/B90Io45Cd2wBUKELeZ+wmjiYF4Efg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=ZHXG8ON1MQAVd0WWgmGngqjNTqPZiPz9LyxrPLzmg1Y9mxBRyPhX4Zk5/ivtnj4n3 eptU/PsHOZLsOUUXwHFNa+8Zr9742CVsM7nWCzeGKTuFDM4VzgjHe4h0BXahzgELZw AFEbkSo/wshrekgHPJScGghJKuijNH54TSiSEgIg= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 5F00E3523108; Wed, 1 Jul 2020 09:03:38 -0700 (PDT) Date: Wed, 1 Jul 2020 09:03:38 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Marco Elver , Nick Desaulniers , Sami Tolvanen , Masahiro Yamada , Will Deacon , Greg Kroah-Hartman , Kees Cook , clang-built-linux , Kernel Hardening , linux-arch , Linux ARM , Linux Kbuild mailing list , LKML , linux-pci@vger.kernel.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" Subject: Re: [PATCH 00/22] add support for Clang LTO Message-ID: <20200701160338.GN9247@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200625080313.GY4817@hirez.programming.kicks-ass.net> <20200625082433.GC117543@hirez.programming.kicks-ass.net> <20200625085745.GD117543@hirez.programming.kicks-ass.net> <20200630191931.GA884155@elver.google.com> <20200630201243.GD4817@hirez.programming.kicks-ass.net> <20200630203016.GI9247@paulmck-ThinkPad-P72> <20200701114027.GO4800@hirez.programming.kicks-ass.net> <20200701140654.GL9247@paulmck-ThinkPad-P72> <20200701150512.GH4817@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200701150512.GH4817@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 01, 2020 at 05:05:12PM +0200, Peter Zijlstra wrote: > On Wed, Jul 01, 2020 at 07:06:54AM -0700, Paul E. McKenney wrote: > > > The current state in the C++ committee is that marking variables > > carrying dependencies is the way forward. This is of course not what > > the Linux kernel community does, but it should not be hard to have a > > -fall-variables-dependent or some such that causes all variables to be > > treated as if they were marked. Though I was hoping for only pointers. > > Are they -sure- that they -absolutely- need to carry dependencies > > through integers??? > > What's 'need'? :-) Turning off all dependency-killing optimizations on all pointers is likely a non-event. Turning off all dependency-killing optimizations on all integers is not the road to happiness. So whatever "need" might be, it would need to be rather earthshaking. ;-) It is probably not -that- hard to convert to pointers, even if they are indexing multiple arrays. > I'm thinking __ktime_get_fast_ns() is better off with a dependent load > than it is with an extra smp_rmb(). > > Yes we can stick an smp_rmb() in there, but I don't like it. Like I > wrote earlier, if I wanted a control dependency, I'd have written one. No argument here. But it looks like we are going to have to tell the compiler. Thanx, Paul