From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261991AbULHG4e (ORCPT ); Wed, 8 Dec 2004 01:56:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262003AbULHG4e (ORCPT ); Wed, 8 Dec 2004 01:56:34 -0500 Received: from ns.virtualhost.dk ([195.184.98.160]:27803 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S261991AbULHG42 (ORCPT ); Wed, 8 Dec 2004 01:56:28 -0500 Date: Wed, 8 Dec 2004 07:55:34 +0100 From: Jens Axboe To: Andrew Morton Cc: Andrea Arcangeli , nickpiggin@yahoo.com.au, linux-kernel@vger.kernel.org Subject: Re: Time sliced CFQ io scheduler Message-ID: <20041208065534.GF3035@suse.de> References: <20041202130457.GC10458@suse.de> <20041202134801.GE10458@suse.de> <20041202114836.6b2e8d3f.akpm@osdl.org> <20041202195232.GA26695@suse.de> <20041208003736.GD16322@dualathlon.random> <1102467253.8095.10.camel@npiggin-nld.site> <20041208013732.GF16322@dualathlon.random> <20041207180033.6699425b.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20041207180033.6699425b.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: > Andrea Arcangeli wrote: > > > > The desktop is ok with "as" simply because it's > > normally optimal to stop writes completely > > AS doesn't "stop writes completely". With the current settings it > apportions about 1/3 of the disk's bandwidth to writes. > > This thing Jens has found is for direct-io writes only. It's a bug. Indeed. It's a special case one, but nasty for that case. > The other problem with AS is that it basically doesn't work at all with a > TCQ depth greater than four or so, and lots of people blindly look at > untuned SCSI benchmark results without realising that. If a distro is That's pretty easy to fix. I added something like that to cfq, and it's not a lot of lines of code (grep for rq_in_driver and cfq_max_depth). > always selecting CFQ then they've probably gone and deoptimised all their > IDE users. Andrew, AS has other issues, it's not a case of AS always being faster at everything. > AS needs another iteration of development to fix these things. Right now > it's probably the case that we need CFQ or deadline for servers and AS for > desktops. That's awkward. Currently I think the time sliced cfq is the best all around. There's still a few kinks to be shaken out, but generally I think the concept is sounder than AS. -- Jens Axboe