From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [DO NOT APPLY] sd take advantage of rotation speed Date: Wed, 25 Jun 2008 19:26:39 +0200 Message-ID: <20080625172638.GE20851@kernel.dk> References: <20080619160342.GJ4392@parisc-linux.org> <20080625134705.GZ20851@kernel.dk> <4862552A.5010900@gmail.com> <48627184.9010609@panasas.com> <20080625165759.GC20851@kernel.dk> <20080625172015.GR4392@parisc-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from brick.kernel.dk ([87.55.233.238]:12425 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752395AbYFYR0l (ORCPT ); Wed, 25 Jun 2008 13:26:41 -0400 Content-Disposition: inline In-Reply-To: <20080625172015.GR4392@parisc-linux.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Matthew Wilcox Cc: Boaz Harrosh , Ric Wheeler , linux-scsi@vger.kernel.org On Wed, Jun 25 2008, Matthew Wilcox wrote: > On Wed, Jun 25, 2008 at 06:57:59PM +0200, Jens Axboe wrote: > > Precisely, merging and fairness is a big part of it. Plus, doing this in > > sd is just a blatant layer violation. > > I'm fine with tweaking the elevators to know about low-latency seeks. > But please stop describing it as "a blatant layering violation". > It's nothing of the sort. It's setting a default at a point where we > find out the information which would guide us. Uhm, but it IS "a blatant layering violation", it's doing things from the wrong side up :-) > I haven't looked into doing this in udev yet; I've got caught up in > another project. In any case, it seems like there's no role for udev > any more, so I'll probably not spend any more time on this unless there's > some need. I don't think udev is a particularly good idea either. My plan was to introduce device profiles for the queue, but it is probably a bad idea to over-engineer this. So I'll keep it simple, stick to a 'zero cost seek' flag instead and allow drivers to signal that. libata/ide needs to check the ID page word to detect SSD drives as well, so they need a few lines of change too. I'll just stick the block bit in the 2.6.27 pending queue and let the other patches go through Jeff/James/Bart. -- Jens Axboe