From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760857AbZBLVQV (ORCPT ); Thu, 12 Feb 2009 16:16:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753560AbZBLVQL (ORCPT ); Thu, 12 Feb 2009 16:16:11 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:36831 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751003AbZBLVQJ (ORCPT ); Thu, 12 Feb 2009 16:16:09 -0500 Date: Thu, 12 Feb 2009 13:15:08 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: "Paul E. McKenney" cc: Mathieu Desnoyers , ltt-dev@lists.casi.polymtl.ca, linux-kernel@vger.kernel.org, Bryan Wu , uclinux-dist-devel@blackfin.uclinux.org Subject: Re: [ltt-dev] [RFC git tree] Userspace RCU (urcu) for Linux (repost) In-Reply-To: <20090212203924.GK6759@linux.vnet.ibm.com> Message-ID: References: <20090211214258.GA32407@Krystal> <20090212003549.GU6694@linux.vnet.ibm.com> <20090212023308.GA21157@linux.vnet.ibm.com> <20090212040824.GA12346@Krystal> <20090212050120.GA8317@linux.vnet.ibm.com> <20090212070539.GA15896@Krystal> <20090212164621.GC6759@linux.vnet.ibm.com> <20090212192941.GC2047@Krystal> <20090212200249.GG6759@linux.vnet.ibm.com> <20090212203924.GK6759@linux.vnet.ibm.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 12 Feb 2009, Paul E. McKenney wrote: > > In other words, you are arguing for using ACCESS_ONCE() in the loops, > but keeping the old ACCESS_ONCE() definition, and declaring BF hardware > broken? Well, I _also_ argue that if you have a busy loop, you'd better have a cpu_relax() in there somewhere anyway. If you don't, you have a bug. So I think the BF approach is "borderline broken", but I think it should work, if BF just has whatever appropriate cache flush in its cpu_relax. Linus