Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760710AbXFBOgQ (ORCPT ); Sat, 2 Jun 2007 10:36:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758915AbXFBOgF (ORCPT ); Sat, 2 Jun 2007 10:36:05 -0400 Received: from brick.kernel.dk ([80.160.20.94]:17457 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757243AbXFBOgE (ORCPT ); Sat, 2 Jun 2007 10:36:04 -0400 Date: Sat, 2 Jun 2007 16:34:39 +0200 From: Jens Axboe To: Tejun Heo Cc: David Chinner , david@lang.hm, Phillip Susi , Neil Brown , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, Stefan Bader , Andreas Dilger Subject: Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. Message-ID: <20070602143438.GB32105@kernel.dk> References: <20070530061723.GY85884050@sgi.com> <20070531002011.GC85884050@sgi.com> <20070531062644.GI32105@kernel.dk> <20070531070307.GK85884050@sgi.com> <20070531070656.GK32105@kernel.dk> <465F8F71.20302@gmail.com> <20070601082140.GP32105@kernel.dk> <46613666.7010800@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46613666.7010800@gmail.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1500 Lines: 36 On Sat, Jun 02 2007, Tejun Heo wrote: > Hello, > > Jens Axboe wrote: > >> Would that be very different from issuing barrier and not waiting for > >> its completion? For ATA and SCSI, we'll have to flush write back cache > >> anyway, so I don't see how we can get performance advantage by > >> implementing separate WRITE_ORDERED. I think zero-length barrier > >> (haven't looked at the code yet, still recovering from jet lag :-) can > >> serve as genuine barrier without the extra write tho. > > > > As always, it depends :-) > > > > If you are doing pure flush barriers, then there's no difference. Unless > > you only guarantee ordering wrt previously submitted requests, in which > > case you can eliminate the post flush. > > > > If you are doing ordered tags, then just setting the ordered bit is > > enough. That is different from the barrier in that we don't need a flush > > of FUA bit set. > > Hmmm... I'm feeling dense. Zero-length barrier also requires only one > flush to separate requests before and after it (haven't looked at the > code yet, will soon). Can you enlighten me? Yeah, that's what the zero-length barrier implementation I posted does. Not sure if you have a question beyond that, if so fire away :-) -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/