From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753580AbXCZKFq (ORCPT ); Mon, 26 Mar 2007 06:05:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753581AbXCZKFq (ORCPT ); Mon, 26 Mar 2007 06:05:46 -0400 Received: from mx1.redhat.com ([66.187.233.31]:33152 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753560AbXCZKFp (ORCPT ); Mon, 26 Mar 2007 06:05:45 -0400 From: David Howells In-Reply-To: <20070325213843.GE22126@xi.wantstofly.org> References: <20070325213843.GE22126@xi.wantstofly.org> <20070323111350.GD3980@xi.wantstofly.org> <20070303111427.GB16944@xi.wantstofly.org> <20070303113305.GB10515@flint.arm.linux.org.uk> <20070321221134.GA22497@xi.wantstofly.org> <16051.1174657433@redhat.com> <20070325211542.GD3593@linux.vnet.ibm.com> To: Lennert Buytenhek Cc: "Paul E. McKenney" , Catalin Marinas , ARM Linux Mailing List , Dan Williams , linux-kernel@vger.kernel.org, torvalds@osdl.org, dhowells@redhat.com Subject: Re: I/O memory barriers vs SMP memory barriers X-Mailer: MH-E 8.0; nmh 1.1; GNU Emacs 22.0.50 Date: Mon, 26 Mar 2007 11:04:11 +0100 Message-ID: <3971.1174903451@redhat.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Lennert Buytenhek wrote: > Does everybody agree on these semantics, though? At least David seems > to think that mb/rmb/wmb aren't required to order normal memory accesses > against each other.. Ummm... I've just realised that your statement here is ambiguous. When you say "aren't required to", do you mean "aren't necessary to" or do you mean "don't have to"? Isn't English a fun language? Anyway, what I meant is that mb() and co. as they stand _must_ do everything smp_mb() and co do respectively, _in_ _addition_ to other side effects. mb() implies smp_mb() rmb() implies smp_rmb() wmb() implies smp_wmb() ... David