From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC] relaxed barrier semantics Date: Mon, 2 Aug 2010 14:48:30 +0200 Message-ID: <20100802124830.GB22345@lst.de> References: <25F5E16E-968D-4FEF-8187-70453985B19B@dilger.ca> <20100729230406.GI4506@thunk.org> <4C52CBFF.6090406@vlnb.net> <20100730130957.GA26894@lst.de> <4C52D2E0.5000609@vlnb.net> <20100730133410.GA27996@lst.de> <4C52D728.6070008@vlnb.net> <20100730142025.GA29341@lst.de> <20100731004756.GC3273@quack.suse.cz> <4C56A01A.1050107@vlnb.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from verein.lst.de ([213.95.11.210]:45085 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753275Ab0HBMtE (ORCPT ); Mon, 2 Aug 2010 08:49:04 -0400 Content-Disposition: inline In-Reply-To: <4C56A01A.1050107@vlnb.net> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Vladislav Bolkhovitin Cc: Jan Kara , Christoph Hellwig , Ted Ts'o , Andreas Dilger , Ric Wheeler , Tejun Heo , Vivek Goyal , jaxboe@fusionio.com, James.Bottomley@suse.de, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp On Mon, Aug 02, 2010 at 02:38:18PM +0400, Vladislav Bolkhovitin wrote: > > Umm, I don't understand you. I think that fsync in particular is an > >example where you have to wait and issue cache flush if the drive has > >volatile write cache. Otherwise you cannot promise to the user data will be > >really on disk in case of crash. So no ordering helps you. > > Isn't there the second wait for journal update? Yes. > A drive can reorder queued SIMPLE requests at any time doesn't matter if > it has volatile write caches or not. I know. > So, if you expect in-order requests > execution (with journal updates you do?), you need to enforce that order > either by ORDERED requests or (local) queue draining. Yes, exactly what I say.