Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752734AbbGNOMW (ORCPT ); Tue, 14 Jul 2015 10:12:22 -0400 Received: from foss.arm.com ([217.140.101.70]:34489 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752069AbbGNOMU (ORCPT ); Tue, 14 Jul 2015 10:12:20 -0400 Date: Tue, 14 Jul 2015 15:12:16 +0100 From: Will Deacon To: "Paul E. McKenney" Cc: Peter Zijlstra , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Benjamin Herrenschmidt Subject: Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Message-ID: <20150714141202.GN16213@arm.com> References: <20150713142109.GE2632@arm.com> <20150713155447.GB19282@twins.programming.kicks-ass.net> <20150713175029.GO2632@arm.com> <20150713202032.GZ3717@linux.vnet.ibm.com> <20150713222346.GE19282@twins.programming.kicks-ass.net> <20150713230405.GB3717@linux.vnet.ibm.com> <20150714100429.GC15448@arm.com> <20150714124540.GC3717@linux.vnet.ibm.com> <20150714125146.GJ16213@arm.com> <20150714140014.GD3717@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150714140014.GD3717@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1761 Lines: 35 On Tue, Jul 14, 2015 at 03:00:14PM +0100, Paul E. McKenney wrote: > On Tue, Jul 14, 2015 at 01:51:46PM +0100, Will Deacon wrote: > > On Tue, Jul 14, 2015 at 01:45:40PM +0100, Paul E. McKenney wrote: > > > On Tue, Jul 14, 2015 at 11:04:29AM +0100, Will Deacon wrote: > > > > Given that RCU is currently the only user of this barrier, how would you > > > > feel about making the barrier local to RCU and not part of the general > > > > memory-barrier API? > > > > > > In theory, no objection. Your thought is to leave the definitions where > > > they are, mark them as being used only by RCU, and removing mention from > > > memory-barriers.txt? Or did you have something else in mind? > > > > Actually, I was thinking of defining them in an RCU header file with an > > #ifdef CONFIG_POWERPC for the smb_mb() version. Then you could have a big > > comment describing the semantics, or put that in an RCU Documentation file > > instead of memory-barriers.txt. > > > > That *should* then mean we notice anybody else trying to use the barrier, > > because they'd need to send patches to either add something equivalent > > or move the definition out again. > > My concern with this approach is that someone putting together a new > architecture might miss this. That said, this approach certainly would > work for the current architectures. I don't think they're any more likely to miss it than with the current situation where the generic code defines the macro as a NOP unless you explicitly override it. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/