From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v2] barriers: introduce smp_mb__release_acquire and update documentation Date: Fri, 9 Oct 2015 13:13:28 +0200 Message-ID: <20151009111328.GA3816@twins.programming.kicks-ass.net> References: <1444215568-24732-1-git-send-email-will.deacon@arm.com> <20151007111915.GF17308@twins.programming.kicks-ass.net> <20151007132317.GK16065@arm.com> <20151007152501.GI3910@linux.vnet.ibm.com> <1444276236.9940.5.camel@ellerman.id.au> <20151008111638.GL3816@twins.programming.kicks-ass.net> <20151008214439.GE3910@linux.vnet.ibm.com> <20151009083138.GU3816@twins.programming.kicks-ass.net> <20151009094039.GD26278@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from bombadil.infradead.org ([198.137.202.9]:54046 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754756AbbJILNi (ORCPT ); Fri, 9 Oct 2015 07:13:38 -0400 Content-Disposition: inline In-Reply-To: <20151009094039.GD26278@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Will Deacon Cc: "Paul E. McKenney" , Michael Ellerman , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Boqun Feng , Anton Blanchard , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org On Fri, Oct 09, 2015 at 10:40:39AM +0100, Will Deacon wrote: > > > - RELEASE -> ACQUIRE _chains_ (on shared variables) preserve causality, > > (because each link is fully ordered) but are not transitive. > > Yup, and that's the same for UNLOCK -> LOCK, too. Agreed, except RELEASE/ACQUIRE is more RCpc than UNLOCK/LOCK. IFF we can get UNLOCK/LOCK as RCsc the chains are strongly transitive, unlike the RELEASE/ACQUIRE chains, which will be weakly so.