From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: [RFC] relaxed barrier semantics Date: Wed, 28 Jul 2010 10:42:14 -0400 Message-ID: <20100728144214.GB16314@redhat.com> References: <20100727165627.GA474@lst.de> <20100727175418.GF6820@quack.suse.cz> <20100727183546.GG7347@redhat.com> <4C4FE58C.8080403@kernel.org> <20100728082447.GA7668@lst.de> <4C4FECFE.9040509@kernel.org> <20100728085048.GA8884@lst.de> <4C4FF136.5000205@kernel.org> <20100728090025.GA9252@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx1.redhat.com ([209.132.183.28]:4103 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754783Ab0G1Om1 (ORCPT ); Wed, 28 Jul 2010 10:42:27 -0400 Content-Disposition: inline In-Reply-To: <20100728090025.GA9252@lst.de> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Christoph Hellwig Cc: Tejun Heo , Jan Kara , jaxboe@fusionio.com, James.Bottomley@suse.de, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, tytso@mit.edu, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp On Wed, Jul 28, 2010 at 11:00:25AM +0200, Christoph Hellwig wrote: > On Wed, Jul 28, 2010 at 10:58:30AM +0200, Tejun Heo wrote: > > I see. It probably would be good to have ordering requirements > > carried in the bio / request, so that filesystems can mix and match > > barriers of different strengths as necesasry. As you seem to be > > already working on it, are you interested in pursuing that direction? > > I've been working on that for a while, but it got a lot more urgent > as there's been an application hit particularly hard by the barrier > semantics on cache less devices and people started getting angry > about it. That's why fixing this for cache less devices has become > a higher priority than solving the big picture. And in the process IO controller cgroup stuff will also benefit otherwise excessive draining on request queue takes away any service differentiation CFQ provides among groups. Vivek