Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752214AbaBJPGG (ORCPT ); Mon, 10 Feb 2014 10:06:06 -0500 Received: from e31.co.us.ibm.com ([32.97.110.149]:37865 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751970AbaBJPGC (ORCPT ); Mon, 10 Feb 2014 10:06:02 -0500 Date: Mon, 10 Feb 2014 07:04:43 -0800 From: "Paul E. McKenney" To: Will Deacon Cc: Peter Zijlstra , Torvald Riegel , Ramana Radhakrishnan , David Howells , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "torvalds@linux-foundation.org" , "akpm@linux-foundation.org" , "mingo@kernel.org" , "gcc@gcc.gnu.org" Subject: Re: [RFC][PATCH 0/5] arch: atomic rework Message-ID: <20140210150443.GJ4250@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1391721423.23421.3898.camel@triegel.csb> <20140206221117.GJ4250@linux.vnet.ibm.com> <1391730288.23421.4102.camel@triegel.csb> <20140207042051.GL4250@linux.vnet.ibm.com> <20140207074405.GM5002@laptop.programming.kicks-ass.net> <20140207165028.GO4250@linux.vnet.ibm.com> <20140207165548.GR5976@mudshark.cambridge.arm.com> <20140207180216.GP4250@linux.vnet.ibm.com> <20140210114813.GJ9987@twins.programming.kicks-ass.net> <20140210114929.GF17766@mudshark.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140210114929.GF17766@mudshark.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14021015-8236-0000-0000-000006EA7F1C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 10, 2014 at 11:49:29AM +0000, Will Deacon wrote: > On Mon, Feb 10, 2014 at 11:48:13AM +0000, Peter Zijlstra wrote: > > On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote: > > > As near as I can tell, compiler writers hate the idea of prohibiting > > > speculative-store optimizations because it requires them to introduce > > > both control and data dependency tracking into their compilers. Many of > > > them seem to hate dependency tracking with a purple passion. At least, > > > such a hatred would go a long way towards explaining the incomplete > > > and high-overhead implementations of memory_order_consume, the long > > > and successful use of idioms based on the memory_order_consume pattern > > > notwithstanding [*]. ;-) > > > > Just tell them that because the hardware provides control dependencies > > we actually use and rely on them. > > s/control/address/ ? Both are important, but as Peter's reply noted, it was control dependencies under discussion. Data dependencies (which include the ARM/PowerPC notion of address dependencies) are called out by the standard already, but control dependencies are not. I am not all that satisified by current implementations of data dependencies, admittedly. Should be an interesting discussion. ;-) Thanx, Paul -- 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/