From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754339Ab3KUWcg (ORCPT ); Thu, 21 Nov 2013 17:32:36 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:41406 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753021Ab3KUWcf (ORCPT ); Thu, 21 Nov 2013 17:32:35 -0500 Date: Thu, 21 Nov 2013 14:32:30 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu Subject: Re: [PATCH v2 RFC 1/3] documentation: Add needed ACCESS_ONCE() calls to memory-barriers.txt Message-ID: <20131121223230.GI4138@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20131121213055.GA6938@linux.vnet.ibm.com> <1385069489-7898-1-git-send-email-paulmck@linux.vnet.ibm.com> <20131121215517.GA16796@laptop.programming.kicks-ass.net> <20131121220950.GG4138@linux.vnet.ibm.com> <20131121221821.GB16796@laptop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131121221821.GB16796@laptop.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13112122-0928-0000-0000-000003EB2C8F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 21, 2013 at 11:18:21PM +0100, Peter Zijlstra wrote: > On Thu, Nov 21, 2013 at 02:09:51PM -0800, Paul E. McKenney wrote: > > On Thu, Nov 21, 2013 at 10:55:17PM +0100, Peter Zijlstra wrote: > > > On Thu, Nov 21, 2013 at 01:31:27PM -0800, Paul E. McKenney wrote: > > > > From: "Paul E. McKenney" > > > > > > > > The Documentation/memory-barriers.txt file was written before the need > > > > for ACCESS_ONCE() was fully appreciated. It therefore contains no > > > > ACCESS_ONCE() calls, which can be a problem when people lift examples > > > > from it. This commit therefore adds ACCESS_ONCE() calls. > > > > > > So I find the repeated ACCESS_ONCE() significantly detracts from the > > > readability of the text. > > > > > > Can't we simply state that all accesses are assumed single-copy atomic > > > and this can be achieved for naturally aligned words using ACCESS_ONCE() > > > in C/C++ ? > > > > We could, but at the moment I would prefer the decrease in readability > > to the copy-and-paste bugs that omit needed ACCESS_ONCE() calls. > > > > Is there some way to get both ACCESS_ONCE() and readability? An > > abbreviation such as AO()? More easily distinguished variable names? > > Something else? > > Use a form that looks less like C and thus defeats copy/paste? My concern with that approach is that there is likely to be a large number of people who are likely to be willing and able to transcribe from any reasonable non-C form to ACCESS_ONCE()-free C code. :-/ But maybe you have something specific in mind? Thanx, Paul