From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH RFC tip/core/rcu 0/15] Remove to-be-unneeded smp_read_barrier_depends() Date: Wed, 11 Oct 2017 05:56:36 -0700 Message-ID: <20171011125636.GX3521@linux.vnet.ibm.com> References: <20171010001951.GA6476@linux.vnet.ibm.com> <26479.1507724463@warthog.procyon.org.uk> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:52222 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753027AbdJKM4n (ORCPT ); Wed, 11 Oct 2017 08:56:43 -0400 Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9BCtDO0043829 for ; Wed, 11 Oct 2017 08:56:43 -0400 Received: from e12.ny.us.ibm.com (e12.ny.us.ibm.com [129.33.205.202]) by mx0a-001b2d01.pphosted.com with ESMTP id 2dhhdrskjd-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 11 Oct 2017 08:56:42 -0400 Received: from localhost by e12.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 11 Oct 2017 08:56:41 -0400 Content-Disposition: inline In-Reply-To: <26479.1507724463@warthog.procyon.org.uk> Sender: linux-arch-owner@vger.kernel.org List-ID: 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 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