From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCH] Implement barrier support for single device DM devices Date: Fri, 15 Feb 2008 15:20:10 +0100 Message-ID: <20080215142010.GA29552@one.firstfloor.org> References: <20080215120821.GA8267@basil.nowhere.org> <20080215122002.GM29914@agk.fab.redhat.com> <47B58EAA.8040405@msgid.tls.msk.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <47B58EAA.8040405@msgid.tls.msk.ru> Sender: linux-kernel-owner@vger.kernel.org To: Michael Tokarev Cc: Andi Kleen , dm-devel@redhat.com, linux-kernel@vger.kernel.org List-Id: dm-devel.ids On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote: > Alasdair G Kergon wrote: > > On Fri, Feb 15, 2008 at 01:08:21PM +0100, Andi Kleen wrote: > >> Implement barrier support for single device DM devices > > > > Thanks. We've got some (more-invasive) dm patches in the works that > > attempt to use flushing to emulate barriers where we can't just > > pass them down like that. > > I wonder if it's worth the effort to try to implement this. DM in theory has some more knowledge for optimization. e.g. for example if it knows that a stream of requests hits only a single device then it can just pass the barriers through again and only flush when there is really a request dependency between different devices. File systems can't do it that fine grained; it's either all or nothing. I don't know if doing it fine grained will much difference in performance though. The only way to find out would be to try it. -Andi