From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752287AbcA0A5o (ORCPT ); Tue, 26 Jan 2016 19:57:44 -0500 Received: from e38.co.us.ibm.com ([32.97.110.159]:58889 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752085AbcA0A5h (ORCPT ); Tue, 26 Jan 2016 19:57:37 -0500 X-IBM-Helo: d03dlp02.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-arch@vger.kernel.org;linux-ia64@vger.kernel.org;linux-kernel@vger.kernel.org;linux-metag@vger.kernel.org;linux-s390@vger.kernel.org;linux-sh@vger.kernel.org;sparclinux@vger.kernel.org Date: Tue, 26 Jan 2016 16:57:30 -0800 From: "Paul E. McKenney" To: Linus Torvalds Cc: Peter Zijlstra , Boqun Feng , Herbert Xu , Leonid Yegoshin , linux-mips , "linux-ia64@vger.kernel.org" , "Michael S. Tsirkin" , Will Deacon , virtualization , Peter Anvin , sparclinux@vger.kernel.org, Ingo Molnar , "linux-arch@vger.kernel.org" , linux-s390 , Russell King - ARM Linux , uml-devel , linux-sh@vger.kernel.org, Michael Ellerman , the arch/x86 maintainers , xen-devel@lists.xenproject.org, Ingo Molnar , linux-xtensa@linux-xtensa.org, James Hogan , Arnd Bergmann , Stefano Stabellini , adi-buildroot-devel@lists.sourceforge.net, David Daney , Thomas Gleixner , linux-metag@vger.kernel.org, "linux-arm-kernel@lists.infradead.org" , Andrew Cooper , Linux Kernel Mailing List , Ralf Baechle , Joe Perches , ppc-dev , David Miller Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h Message-ID: <20160127005730.GE4503@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20160118081929.GA30420@gondor.apana.org.au> <20160118154629.GB3818@linux.vnet.ibm.com> <20160126165207.GB6029@fixme-laptop.cn.ibm.com> <20160126172227.GG6357@twins.programming.kicks-ass.net> <20160126201037.GU4503@linux.vnet.ibm.com> <20160126232921.GY4503@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16012700-0029-0000-0000-00000FF7717B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 26, 2016 at 03:45:23PM -0800, Linus Torvalds wrote: > On Tue, Jan 26, 2016 at 3:29 PM, Paul E. McKenney > wrote: > > > > No trailing data-dependent read, so agreed, no smp_read_barrier_depends() > > needed. That said, I believe that we should encourage rcu_dereference*() > > or lockless_dereference() instead of READ_ONCE() for documentation > > reasons, though. > > I agree that that is likely the right thing to do in pretty much all situations. > > In theory, there might be performance situations where we'd want to > actively avoid the smp_read_barrier_depends() inherent in those, but > considering that it's only a performance issue on alpha, and we > probably have all of two or three people using Linux on alpha, it's a > pretty theoretical performance worry. Agreed! Thanx, Paul