Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751247AbWIKRXy (ORCPT ); Mon, 11 Sep 2006 13:23:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751261AbWIKRXy (ORCPT ); Mon, 11 Sep 2006 13:23:54 -0400 Received: from mail-in-06.arcor-online.net ([151.189.21.46]:413 "EHLO mail-in-01.arcor-online.net") by vger.kernel.org with ESMTP id S1751247AbWIKRXx (ORCPT ); Mon, 11 Sep 2006 13:23:53 -0400 In-Reply-To: References: Mime-Version: 1.0 (Apple Message framework v750) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: Cc: "Paul E. McKenney" , Oliver Neukum , David Howells , Kernel development list Content-Transfer-Encoding: 7bit From: Segher Boessenkool Subject: Re: Uses for memory barriers Date: Mon, 11 Sep 2006 19:23:49 +0200 To: Alan Stern X-Mailer: Apple Mail (2.750) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 763 Lines: 21 > This can't be right. Together 1 and 2 would obviate the need for > wmb(). > The CPU doing "STORE A; STORE B" will always see the operations > occuring > in program order by 1, and hence every other CPU would always see them > occurring in the same order by 2 -- even without wmb(). > > Either 2 is too strong, or else what you mean by "perceived" isn't > sufficiently clear. 2. is only for multiple stores to a _single_ memory location -- you use wmb() to order stores to _separate_ memory locations. Segher - 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/