From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC] relaxed barrier semantics Date: Fri, 30 Jul 2010 15:12:05 +0200 Message-ID: <20100730131205.GA27348@lst.de> References: <20100728092859.GA11096@lst.de> <20100729014431.GD4506@thunk.org> <4C51DA1F.2040701@redhat.com> <20100729194904.GA17098@lst.de> <4C51DCF1.3010507@redhat.com> <1280433591.4441.393.camel@mulgrave.site> <20100729200327.GA17767@lst.de> <4C52C994.2040405@vlnb.net> <20100730125750.GB26118@lst.de> <4C52CF20.6090404@vlnb.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from verein.lst.de ([213.95.11.210]:40077 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755895Ab0G3NMd (ORCPT ); Fri, 30 Jul 2010 09:12:33 -0400 Content-Disposition: inline In-Reply-To: <4C52CF20.6090404@vlnb.net> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Vladislav Bolkhovitin Cc: Christoph Hellwig , James Bottomley , Ric Wheeler , Ted Ts'o , Tejun Heo , Vivek Goyal , Jan Kara , jaxboe@fusionio.com, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp On Fri, Jul 30, 2010 at 05:09:52PM +0400, Vladislav Bolkhovitin wrote: > Sorry, I can't follow you here. What was the load pattern difference > between the tests in the way how the backend device saw it? I thought, > it was only in absence of the cache flush commands (SYNCHRONIZE_CACHE?) > in the write through case, but looks like there is something more different? The only difference in commands is that we see no SYNCHRONIZE_CACHE. The big picture difference is that we also only drain the queue just to undrain it ASAP, instead of keeping it drained over a sequence of SYNCHRONIZE_CACHE + WRITE + SYNCHRONIZE_CACHE, which can make a huge difference for a device with very low latencies like the SSD in my laptop.