From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: I/O write ordering Date: 22 Sep 2004 10:47:59 -0400 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <1095864485.2143.1.camel@mulgrave> References: <1095789421.2467.414.camel@mulgrave> <200409211409.11095.jbarnes@engr.sgi.com> <20040921190625.GB11708@colo.lackof.org> <20040921210341.GC146363@sgi.com> <20040921211108.GA16153@parcelfarce.linux.theplanet.co.uk> <20040921214302.GG146363@sgi.com> <20040922000211.GE16153@parcelfarce.linux.theplanet.co.uk> <20040922011652.GD147856@sgi.com> <20040922014428.GD20053@colo.lackof.org> <20040922025805.GA148414@sgi.com> <20040922143208.GL16153@parcelfarce.linux.theplanet.co.uk> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from stat16.steeleye.com ([209.192.50.48]:2018 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S265970AbUIVOsx (ORCPT ); Wed, 22 Sep 2004 10:48:53 -0400 In-Reply-To: <20040922143208.GL16153@parcelfarce.linux.theplanet.co.uk> List-Id: linux-scsi@vger.kernel.org To: Matthew Wilcox Cc: Jeremy Higdon , Grant Grundler , Jesse Barnes , Matthew Wilcox , Andrew Vasquez , pj@sgi.com, SCSI Mailing List , mdr@cthulhu.engr.sgi.com, jeremy@cthulhu.engr.sgi.com, djh@cthulhu.engr.sgi.com, Andrew Morton , Benjamin Herrenschmidt , Richard Henderson , Paul Mackerras On Wed, 2004-09-22 at 10:32, Matthew Wilcox wrote: > I think the only disagreement is whether we have it implicit or explicit. > I see three potential solutions: > > 1. iomb() [we have mb(), rmb(), wmb() already. Does mb() imply iomb()? > Vice versa?] > 2. io_spin_unlock() which is an io barrier as well as a memory barrier. > 3. Make spin_unlock an io barrier. Expensive. > > I'd quite like to hear opinions from the PPC and Alpha people, they seem to > be the most out-of-order architectures. I favour 1. iomb; I think, since I/O barriers can be either heavyweight or non-existent depending on the architecture, iomb() should imply mb() but not vice versa. James