From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from stat16.steeleye.com ([209.192.50.48]:13769 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S268158AbUIWT1m (ORCPT ); Thu, 23 Sep 2004 15:27:42 -0400 Subject: Re: [PATCH] I/O space write barrier From: James Bottomley In-Reply-To: <200409231507.26672.jbarnes@engr.sgi.com> References: <200409231448.21887.jbarnes@engr.sgi.com> <1095966238.3043.26.camel@mulgrave> <200409231507.26672.jbarnes@engr.sgi.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: 23 Sep 2004 15:27:24 -0400 Message-Id: <1095967651.2157.42.camel@mulgrave> Mime-Version: 1.0 To: Jesse Barnes Cc: linux-arch@vger.kernel.org, jeremy@sgi.com List-ID: On Thu, 2004-09-23 at 15:07, Jesse Barnes wrote: > If we're waiting for an interrupt here, I don't think it matters if we flush > or order, we'll wait the same amount of time regardless. I don't think so. Your ordering barrier doesn't cause a posted write flush. Posted writes have theoretically no upper limit defined in the spec for the time they may remain posted, so in the former case, you are guaranteed that by the time you set the flag and exit the function that interrupts are enabled in the qla1280. If you apply the patch you sent in, this guarantee is broken and you don't really know how much longer after exiting the function it will be before interrupts become enabled (although in practice it's probably only of the order of ms). James