Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753187AbYKGUI0 (ORCPT ); Fri, 7 Nov 2008 15:08:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751324AbYKGUIQ (ORCPT ); Fri, 7 Nov 2008 15:08:16 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.123]:56035 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751121AbYKGUIP (ORCPT ); Fri, 7 Nov 2008 15:08:15 -0500 Date: Fri, 7 Nov 2008 15:08:12 -0500 (EST) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Mathieu Desnoyers cc: David Howells , "Paul E. McKenney" , Linus Torvalds , akpm@linux-foundation.org, Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, Nicolas Pitre , Ralf Baechle , benh@kernel.crashing.org, paulus@samba.org, David Miller , Ingo Molnar , Thomas Gleixner , linux-arch@vger.kernel.org Subject: Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb() In-Reply-To: <20081107170902.GD22134@Krystal> Message-ID: References: <20081107053349.861709786@polymtl.ca> <20081107052336.652868737@polymtl.ca> <25257.1226055312@redhat.com> <20081107170902.GD22134@Krystal> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 868 Lines: 35 On Fri, 7 Nov 2008, Mathieu Desnoyers wrote: > > I want to make sure > > __m_cnt_hi > is read before > mmio cnt_lo read Hmm, let me make sure I understand why there is no wmb. Paul, can you verify this? Mathieu, you do the following: read a smp_rmb reab b if (test b) write a So the idea is that you must read b to test it. And since we must read a before reading b we can see that we write a before either? The question remains, can the write happen before either of the reads? But since the read b is reading the hw clock, perhaps that just implies a wmb on the hardware side? -- Steve -- 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/