From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ted Ts'o Subject: Re: [RFC] relaxed barrier semantics Date: Thu, 29 Jul 2010 20:19:56 -0400 Message-ID: <20100730001956.GJ4506@thunk.org> References: <4C4FF592.9090800@kernel.org> <20100728092859.GA11096@lst.de> <20100729014431.GD4506@thunk.org> <4C51DA1F.2040701@redhat.com> <20100729194904.GA17098@lst.de> <4C51DCF1.3010507@redhat.com> <25F5E16E-968D-4FEF-8187-70453985B19B@dilger.ca> <20100729230406.GI4506@thunk.org> <1280446105.4441.837.camel@mulgrave.site> <1280446655.4441.863.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , Ric Wheeler , Christoph Hellwig , 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 To: James Bottomley Return-path: Content-Disposition: inline In-Reply-To: <1280446655.4441.863.camel@mulgrave.site> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Jul 29, 2010 at 06:37:35PM -0500, James Bottomley wrote: > Actually, just an update on this now that I've taken my SCSI glasses > off. Anything that does tagging properly ... like SCSI or SATA NCQ > shouldn't have this problem because the multiple outstanding tags hide > the media access latency. For untagged devices, yes, it will be > painful. > Maybe I'm just being too paranoid and not trusting enough about the competence of firmware authors, but let's do a lot of testing on this first. Or let's have some options so we can turn off FUA if it turns out to be a disaster on a particular device. I'll have to do some searching, but I distinctly remember reading an article in Ars Technical or Anandtech about how FUA wasn't all that useful because what the writer had seen in terms of testing some specific devices. Maybe that was a while ago and devices have gotten better, and maybe that writer was on crack, but given that FUA doesn't get used a lot, I'm nervous.... - Ted