From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262069AbULHHmW (ORCPT ); Wed, 8 Dec 2004 02:42:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262039AbULHHjX (ORCPT ); Wed, 8 Dec 2004 02:39:23 -0500 Received: from ns.virtualhost.dk ([195.184.98.160]:43944 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S262062AbULHHha (ORCPT ); Wed, 8 Dec 2004 02:37:30 -0500 Date: Wed, 8 Dec 2004 08:36:37 +0100 From: Jens Axboe To: Andrew Morton Cc: nickpiggin@yahoo.com.au, andrea@suse.de, linux-kernel@vger.kernel.org Subject: Re: Time sliced CFQ io scheduler Message-ID: <20041208073637.GF19522@suse.de> References: <1102467253.8095.10.camel@npiggin-nld.site> <20041208013732.GF16322@dualathlon.random> <20041207180033.6699425b.akpm@osdl.org> <20041208022020.GH16322@dualathlon.random> <20041207182557.23eed970.akpm@osdl.org> <1102473213.8095.34.camel@npiggin-nld.site> <20041208065858.GH3035@suse.de> <1102490086.8095.63.camel@npiggin-nld.site> <20041208072052.GC19522@suse.de> <20041207233027.20f29a16.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20041207233027.20f29a16.akpm@osdl.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 07 2004, Andrew Morton wrote: > Jens Axboe wrote: > > > > I think we need to end up with something that sets the machine profile > > for the interesting disks. Some things you can check for at runtime > > (like the writes being extremely fast is a good indicator of write > > caching), but it is just not possible to cover it all. Plus, you end up > > with 30-40% of the code being convoluted stuff added to detect it. > > We can detect these things from userspace. Parse the hdparm/scsiinfo > output, then poke numbers into /sys tunables. The simple things, like cache settings and queue depth - definitely. The harder things like how does this drive behave you cannot. And unfortunately the former is also pretty easy to control (at least for the depth) and at least gather at runtime. So I think a user mode helper only makes sense if it can help you with real drive characteristics that are hard to detect. Plus, settings have a nack for changing while we are running as well. Hmm so perhaps not such a hot idea after all. I don't envision anyone actually doing it anyways, so... -- Jens Axboe