From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757364AbdJKM4t (ORCPT ); Wed, 11 Oct 2017 08:56:49 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:37024 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752086AbdJKM4o (ORCPT ); Wed, 11 Oct 2017 08:56:44 -0400 Date: Wed, 11 Oct 2017 05:56:36 -0700 From: "Paul E. McKenney" To: David Howells Cc: linux-kernel@vger.kernel.org, mark.rutland@arm.com, linux-arch@vger.kernel.org, viro@zeniv.linux.org.uk, tj@kernel.org, cl@linux.com, davem@davemloft.net, peterz@infradead.org, mingo@redhat.com, rostedt@goodmis.org, akpm@linux-foundation.org, corbet@lwn.net, james.l.morris@oracle.com, torvalds@linux-foundation.org Subject: Re: [PATCH RFC tip/core/rcu 0/15] Remove to-be-unneeded smp_read_barrier_depends() Reply-To: paulmck@linux.vnet.ibm.com References: <20171010001951.GA6476@linux.vnet.ibm.com> <26479.1507724463@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <26479.1507724463@warthog.procyon.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17101112-0048-0000-0000-000001F4001D X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007878; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000235; SDB=6.00929588; UDB=6.00467880; IPR=6.00709859; 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=3.00017490; XFM=3.00000015; UTC=2017-10-11 12:56:41 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17101112-0049-0000-0000-000042D5CE25 Message-Id: <20171011125636.GX3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-11_05:,, 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-1710110178 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 11, 2017 at 01:21:03PM +0100, David Howells wrote: > Paul E. McKenney wrote: > > > Will Deacon has proposed adding smp_read_barrier_depends() to READ_ONCE(), > > which would mean that quite a few instances of smp_read_barrier_depends() > > would become redundant. > > It's not clear from you description where the barrier is added in relation to > the read: before, after or both? After, similar to lockless_dereference(). Of course, there is not really a barrier except for on Alpha. Thanx, Paul