From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 20826 invoked by alias); 10 Feb 2014 11:48:19 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 20815 invoked by uid 89); 10 Feb 2014 11:48:19 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.5 required=5.0 tests=AWL,BAYES_00,RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: merlin.infradead.org Received: from merlin.infradead.org (HELO merlin.infradead.org) (205.233.59.134) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Mon, 10 Feb 2014 11:48:18 +0000 Received: from dhcp-077-248-225-117.chello.nl ([77.248.225.117] helo=twins) by merlin.infradead.org with esmtpsa (Exim 4.80.1 #2 (Red Hat Linux)) id 1WCpLU-0000iw-KP; Mon, 10 Feb 2014 11:48:16 +0000 Received: by twins (Postfix, from userid 1000) id E86DB8278359; Mon, 10 Feb 2014 12:48:13 +0100 (CET) Date: Mon, 10 Feb 2014 11:48:00 -0000 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Will Deacon , 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: <20140210114813.GJ9987@twins.programming.kicks-ass.net> References: <20140206185910.GE27276@mudshark.cambridge.arm.com> <20140206192743.GH4250@linux.vnet.ibm.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140207180216.GP4250@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) X-SW-Source: 2014-02/txt/msg00120.txt.bz2 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. Not that I expect they care too much what we do, given the current state of things.