From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752742AbdJKQDA (ORCPT ); Wed, 11 Oct 2017 12:03:00 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:54902 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751527AbdJKQC5 (ORCPT ); Wed, 11 Oct 2017 12:02:57 -0400 Date: Wed, 11 Oct 2017 09:02:52 -0700 From: "Paul E. McKenney" To: David Howells Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, linux-arch@vger.kernel.org, peterz@infradead.org, will.deacon@arm.com, Jonathan Corbet , Alexander Kuleshov Subject: Re: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends() Reply-To: paulmck@linux.vnet.ibm.com References: <20171011125857.GY3521@linux.vnet.ibm.com> <20171010155042.GD3521@linux.vnet.ibm.com> <1507594969-8347-12-git-send-email-paulmck@linux.vnet.ibm.com> <20171010001951.GA6476@linux.vnet.ibm.com> <8079.1507628146@warthog.procyon.org.uk> <26455.1507724399@warthog.procyon.org.uk> <6544.1507735704@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6544.1507735704@warthog.procyon.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17101116-0036-0000-0000-0000027A17F9 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007878; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000236; SDB=6.00929650; UDB=6.00467917; IPR=6.00709921; BA=6.00005634; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017491; XFM=3.00000015; UTC=2017-10-11 16:02:55 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17101116-0037-0000-0000-0000420B3AAA Message-Id: <20171011160252.GF3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-11_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710110221 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 11, 2017 at 04:28:24PM +0100, David Howells wrote: > Paul E. McKenney wrote: > > > Placing the comment on the same line makes it less likely that some > > later change will move the comment away from the load that it applies to. > > The problem with your 'address dep' comment is that it's not particularly > useful. > > Either your comment needs to say "dep between X and Y", but if the following is > always the dep: > > Y = READ_ONCE(X) > access(*Y) > > then the comment is superfluous. In assoc_array.c, the access is often quite some distance from the corresponding READ_ONCE(). > If it's not always true then your comment needs to indicate what the dependency > is. Given that most READ_ONCE() calls aren't heading dependency chains, a comment indicating that a particular READ_ONCE() does head a dependency chain does provide at least some information. But, as you say below... > The other thing your comment could/should say is where the other barrier is - > barriers always have to be paired as a general rule. (I know I haven't put > these comments in here - but I've been doing that recently). I would welcome a patch that added the comments or help with what the comments should say. Thanx, Paul