From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759214AbYJKQtu (ORCPT ); Sat, 11 Oct 2008 12:49:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754523AbYJKQtk (ORCPT ); Sat, 11 Oct 2008 12:49:40 -0400 Received: from casper.infradead.org ([85.118.1.10]:53158 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754329AbYJKQtj (ORCPT ); Sat, 11 Oct 2008 12:49:39 -0400 Date: Sat, 11 Oct 2008 09:49:30 -0700 From: Arjan van de Ven To: James Bottomley Cc: Jens Axboe , Alan Cox , Linux Kernel Mailing List , linux-ide@vger.kernel.org, torvalds@osdl.org Subject: Re: libata: set queue SSD flag for SSD devices Message-ID: <20081011094930.3cf55ea5@infradead.org> In-Reply-To: <1223743124.4159.27.camel@localhost.localdomain> References: <200810101904.m9AJ42Gq018897@hera.kernel.org> <20081010202515.446857cc@lxorguk.ukuu.org.uk> <20081010200528.GJ19428@kernel.dk> <20081010175508.3d1ed2a4@infradead.org> <1223710417.4159.11.camel@localhost.localdomain> <20081011140600.GR19428@kernel.dk> <1223739853.4159.17.camel@localhost.localdomain> <20081011090407.6de9b8b4@infradead.org> <1223743124.4159.27.camel@localhost.localdomain> Organization: Intel X-Mailer: Claws Mail 3.5.0 (GTK+ 2.12.12; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 11 Oct 2008 18:38:44 +0200 James Bottomley wrote: > On Sat, 2008-10-11 at 09:04 -0700, Arjan van de Ven wrote: > > On Sat, 11 Oct 2008 17:44:13 +0200 > > James Bottomley wrote: > > > > > > > > > So we need something a bit more involved, but not too complex. A > > > > fine line... > > > > > > It's a policy ... just let userspace do it so the user can tune > > > it. That's what EMC does now (except I think they key of inquiry > > > strings rather than cache size). > > > > > > while the chosen elevator obviously is policy, the kernel really > > should pick a sensible default based on what it knows. > > Lets put it this way: if userland needs to do a tuning to the kernel > > based on data only provided by the kernel, and will always do it the > > same way, we should have made that choice the default policy in the > > kernel in the first place. > > Well, this is a bit of a nasty layering problem. We certainly don't > want the Block layer to know how to poke at SATA, SCSI and other > esoteric media to see what elevator should be the default, so we'd > have to craft a new block API that the lower subsystems would > implement for this. I'm really not sure it's worth the trouble when > the boot system can do it simply from userspace, but I'll defer to > Jens. > these devices already give the elevator layer information about the device, like optimal/max io size etc. having the elevator take a "don't bother optimizing for seeks" flag is very much along the same lines, it's a device property that the elevator needs to learn about in order to send the right kinds of IO down. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org