From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750741AbbHQEGR (ORCPT ); Mon, 17 Aug 2015 00:06:17 -0400 Received: from ozlabs.org ([103.22.144.67]:43885 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750732AbbHQEGP (ORCPT ); Mon, 17 Aug 2015 00:06:15 -0400 Message-ID: <1439784367.14494.3.camel@ellerman.id.au> Subject: Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() From: Michael Ellerman To: paulmck@linux.vnet.ibm.com Cc: Will Deacon , Peter Zijlstra , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Benjamin Herrenschmidt Date: Mon, 17 Aug 2015 14:06:07 +1000 In-Reply-To: <20150812154346.GR3895@linux.vnet.ibm.com> References: <20150714125146.GJ16213@arm.com> <20150714140014.GD3717@linux.vnet.ibm.com> <20150714141202.GN16213@arm.com> <20150714193144.GP3717@linux.vnet.ibm.com> <20150715013820.GA21971@linux.vnet.ibm.com> <20150715105135.GE1005@arm.com> <20150715131221.GY3717@linux.vnet.ibm.com> <20150724113101.GE30410@arm.com> <20150724153046.GJ3717@linux.vnet.ibm.com> <20150812134415.GC23540@arm.com> <20150812154346.GR3895@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11-0ubuntu3 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2015-08-12 at 08:43 -0700, Paul E. McKenney wrote: > On Wed, Aug 12, 2015 at 02:44:15PM +0100, Will Deacon wrote: > > Hello Paul, > > > > On Fri, Jul 24, 2015 at 04:30:46PM +0100, Paul E. McKenney wrote: > > > On Fri, Jul 24, 2015 at 12:31:01PM +0100, Will Deacon wrote: > > > > On Wed, Jul 15, 2015 at 02:12:21PM +0100, Paul E. McKenney wrote: > > > > > > > commit 695c05d4b9666c50b40a1c022678b5f6e2e3e771 > > > > > > > Author: Paul E. McKenney > > > > > > > Date: Tue Jul 14 18:35:23 2015 -0700 > > > > > > > > > > > > > > rcu,locking: Privatize smp_mb__after_unlock_lock() > > > > > > > > > > > > > > RCU is the only thing that uses smp_mb__after_unlock_lock(), and is > > > > > > > likely the only thing that ever will use it, so this commit makes this > > > > > > > macro private to RCU. > > > > > > > > > > > > > > Signed-off-by: Paul E. McKenney > > > > > > > Cc: Will Deacon > > > > > > > Cc: Peter Zijlstra > > > > > > > Cc: Benjamin Herrenschmidt > > > > > > > Cc: "linux-arch@vger.kernel.org" > > > > > > > > Are you planning to queue this somewhere? I think it makes sense regardless > > > > of whether we change PowerPc or not and ideally it would be merged around > > > > the same time as my relaxed atomics series. > > > > > > I have is in -rcu. By default, I will push it to the 4.4 merge window. > > > Please let me know if you need it sooner. > > > > The generic relaxed atomics are now queued in -tip, so it would be really > > good to see this Documentation update land in 4.3 if at all possible. I > > appreciate it's late in the cycle, but it's always worth asking. > > Can't hurt to give it a try. I have set -rcu's rcu/next branch to this > commit, and if it passes a few day's worth of testing, I will see what > Ingo has to say about a pull request. > > This commit also privatizes smp_mb__after_unlock_lock() as well as > updating documentation. Looks like we need to strengthen powerpc's > locking primitives, then get rid of smp_mb__after_unlock_lock() entirely. > Or did that already happen and I just missed it? No it didn't. I thought the end result of this thread was that we didn't *need* to change the powerpc lock semantics? Or did I read it wrong? ie. the docs now say that RELEASE+ACQUIRE is not a full barrier, which is consistent with our current implementation. cheers