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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 DDE2AC433E0 for ; Wed, 1 Jul 2020 16:05:20 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AF3A2206BE for ; Wed, 1 Jul 2020 16:05:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="MY01WvD5"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZHXG8ON1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF3A2206BE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:Reply-To:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=f+ln6Ex5juOio4mdMfdTkvIyoeGlXJYwbcoBW/h7YMM=; b=MY01WvD5E0Ux7Ei1qbHvQAbfdO kYyZpwrI4v98xf20Z+xTW61UpIzcC19x7as7K7XvMVyi5tUf/cfmPvX0qevB37ymTuy4MZRMgiXgz BN4veGb7WNAHSi2Yz1yCd9Y1zg18NZ1VcBHP6tAE4/aAOTsfyQM8ZW26Lhxl1+1eeliCO+IXSjLhR 4Z87fU0M1PR6Vts3GPiErC9G28VfElOGFYJkopz6GZEQ6ki+PtrJY+EoDrb2L5SOWpZ1yJXbg1q6J QOh1ARRO/ZNwErJKubvfEBhfOhegWDVkL9iqOYLcy4joL+Ian7+EbGb7HiY6IY8mhfLh/7GeCfa3X h0HGeZ0w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqfD6-0008Nu-6p; Wed, 01 Jul 2020 16:03:44 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqfD1-0008LG-AT for linux-arm-kernel@lists.infradead.org; Wed, 01 Jul 2020 16:03:40 +0000 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 Subject: Re: [PATCH 00/22] add support for Clang LTO Message-ID: <20200701160338.GN9247@paulmck-ThinkPad-P72> 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-Disposition: inline In-Reply-To: <20200701150512.GH4817@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200701_120339_507874_3E5818D6 X-CRM114-Status: GOOD ( 21.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paulmck@kernel.org Cc: linux-arch , Marco Elver , "maintainer:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" , Kees Cook , Kernel Hardening , Greg Kroah-Hartman , Masahiro Yamada , Linux Kbuild mailing list , Nick Desaulniers , LKML , clang-built-linux , Sami Tolvanen , linux-pci@vger.kernel.org, Will Deacon , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel