From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751972AbWISTfQ (ORCPT ); Tue, 19 Sep 2006 15:35:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751979AbWISTfQ (ORCPT ); Tue, 19 Sep 2006 15:35:16 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:3048 "EHLO e3.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1751972AbWISTfO (ORCPT ); Tue, 19 Sep 2006 15:35:14 -0400 Date: Tue, 19 Sep 2006 12:36:05 -0700 From: "Paul E. McKenney" To: Nick Piggin Cc: Alan Stern , David Howells , Kernel development list Subject: Re: Uses for memory barriers Message-ID: <20060919193604.GI1310@us.ibm.com> Reply-To: paulmck@us.ibm.com References: <45102E21.2060301@yahoo.com.au> <20060919181919.GG1310@us.ibm.com> <45103B8D.1040006@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45103B8D.1040006@yahoo.com.au> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 20, 2006 at 04:48:45AM +1000, Nick Piggin wrote: > Paul E. McKenney wrote: > >On Wed, Sep 20, 2006 at 03:51:29AM +1000, Nick Piggin wrote: > > >>If store forwarding is able to occur outside cache coherency protocol, > >>then I don't see why not. I would also be interested to know if this > >>is the case on real systems. > > > > > >We are discussing multiple writes to the same variable, correct? > > > >Just checking... > > Correct. I am having a hard time seeing how this would happen. Sooner or later, the cacheline comes to the store queue, defining the ordering. All changes that occurred in the store queue while waiting for the cache line appear to other CPUs as having happened in very quick succession while the cacheline resides with the store queue in question. So, what am I missing? Thanx, Paul