From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757949AbXJANV1 (ORCPT ); Mon, 1 Oct 2007 09:21:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756164AbXJANO6 (ORCPT ); Mon, 1 Oct 2007 09:14:58 -0400 Received: from mx1.redhat.com ([66.187.233.31]:44061 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756158AbXJANO4 (ORCPT ); Mon, 1 Oct 2007 09:14:56 -0400 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20070929132848.GA21169@wotan.suse.de> References: <20070929132848.GA21169@wotan.suse.de> To: Nick Piggin Cc: dhowells@redhat.com, Linus Torvalds , Paul McKenney , Linux Kernel Mailing List , Andi Kleen Subject: Re: [rfc][patch] i386: remove comment about barriers X-Mailer: MH-E 8.0.3; nmh 1.2-20070115cvs; GNU Emacs 22.1.50 Date: Mon, 01 Oct 2007 14:14:44 +0100 Message-ID: <29721.1191244484@redhat.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote: > [ This is true for x86's sfence/lfence, but raises a question about Linux's > memory barriers. Does anybody expect that a sequence of smp_wmb and smp_rmb > would ever provide a full smp_mb barrier? I've always assumed no, but I > don't know if it is actually documented? ] I think you have to assume that smp_wmb() only orders stores and write barriers, and that smp_rmb() only orders reads and read barriers. smp_mb() implies both smp_wmb() and smp_rmb(), but is greater than the combination of the two. David