From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 30 Jan 2003 13:56:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 30 Jan 2003 13:56:37 -0500 Received: from dbl.q-ag.de ([80.146.160.66]:60070 "EHLO dbl.q-ag.de") by vger.kernel.org with ESMTP id ; Thu, 30 Jan 2003 13:56:35 -0500 Message-ID: <3E39778E.90302@colorfullife.com> Date: Thu, 30 Jan 2003 20:05:50 +0100 From: Manfred Spraul User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2) Gecko/20021202 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrea Arcangeli CC: Stephen Hemminger , Richard Henderson , linux-kernel@vger.kernel.org Subject: Re: frlock and barrier discussion References: <3E396CF1.5000300@colorfullife.com> <20030130182622.GR18538@dualathlon.random> In-Reply-To: <20030130182622.GR18538@dualathlon.random> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrea Arcangeli wrote: >On Thu, Jan 30, 2003 at 07:20:33PM +0100, Manfred Spraul wrote: > > >>Stephen wrote: >> >>[snip - memory barrier for fr_write_begin] >> >> >> >>>Using mb() is more paranoid than necessary. >>> >>> >>What about the memory barrier in fr_read_begin? >>If I understand the Intel documentation correctly, then i386 doesn't need >>them: >>"Writes by a single processor are observed in the same order by all >>processors" >> >>I think "smp_read_barrier_depends()" (i.e. a nop for i386) is sufficient. >> >> > >I don't see what you mean, there is no dependency we can rely on between >the read of the sequence number and the critical section reads, the >critical section reads has nothing to do with the sequence number reads >and the frlock itself. > You are right - "observed in the same order by all processors" only means that the memory interface of the cpus see all writes in order, not that instruction executed by the cpus will observe the writes in order. That leaves ia64 with the acquire/release barriers. -- Manfred