From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757083AbXI2TNG (ORCPT ); Sat, 29 Sep 2007 15:13:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754904AbXI2TMz (ORCPT ); Sat, 29 Sep 2007 15:12:55 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:53811 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751065AbXI2TMz (ORCPT ); Sat, 29 Sep 2007 15:12:55 -0400 X-AuthUser: davidel@xmailserver.org Date: Sat, 29 Sep 2007 12:12:52 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Nick Piggin cc: Linus Torvalds , Paul McKenney , David Howells , Linux Kernel Mailing List , Andi Kleen Subject: Re: [rfc][patch] i386: remove comment about barriers In-Reply-To: <20070929132848.GA21169@wotan.suse.de> Message-ID: References: <20070929132848.GA21169@wotan.suse.de> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 29 Sep 2007, 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? ] No, that can't be. rmb+wmb can't be considered a full mb. There was a recent discussion about this in the thread originated by peterz scalable rw_mutex patches. - Davide