From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: MMIO and gcc re-ordering issue Date: Thu, 12 Jun 2008 09:07:16 -0600 Message-ID: <20080612150716.GX30405@parisc-linux.org> References: <1211852026.3286.36.camel@pasglop> <4843C3D7.7000609@sgi.com> <200806031433.12460.nickpiggin@yahoo.com.au> <200806030952.10360.jbarnes@virtuousgeek.org> <4847A690.302@sgi.com> <1212655433.9496.109.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from palinux.external.hp.com ([192.25.206.14]:56528 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752573AbYFLPHe (ORCPT ); Thu, 12 Jun 2008 11:07:34 -0400 Content-Disposition: inline In-Reply-To: <1212655433.9496.109.camel@pasglop> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Benjamin Herrenschmidt Cc: Jes Sorensen , Jesse Barnes , Nick Piggin , Jeremy Higdon , Roland Dreier , Arjan van de Ven , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, tpiepho@freescale.com, linuxppc-dev@ozlabs.org, scottwood@freescale.com, torvalds@linux-foundation.org, David Miller , alan@lxorguk.ukuu.org.uk On Thu, Jun 05, 2008 at 06:43:53PM +1000, Benjamin Herrenschmidt wrote: > Note that the powerpc implementation currently clears the flag > on spin_lock and tests it on unlock. We are considering changing > that to not touch the flag on spin_lock and just clear it whenever > we do a sync (ie, on unlock, on explicit mmiowb, and possibly even > on readl's where we happen to do sync's). Your current scheme sounds like it's broken for spin_lock(a) writel(); spin_lock(b); spin_unlock(b); spin_unlock(a); -- Intel are signing my paycheques ... these opinions are still mine "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step."