From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755253Ab2DJN4o (ORCPT ); Tue, 10 Apr 2012 09:56:44 -0400 Received: from merlin.infradead.org ([205.233.59.134]:38711 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750885Ab2DJN4n (ORCPT ); Tue, 10 Apr 2012 09:56:43 -0400 Message-ID: <4F843C17.5050004@kernel.dk> Date: Tue, 10 Apr 2012 15:56:39 +0200 From: Jens Axboe MIME-Version: 1.0 To: Vivek Goyal CC: linux kernel mailing list , Moyer Jeff Moyer Subject: Re: [RFC PATCH] block: Change default IO scheduler to deadline except SATA References: <20120410133708.GE21801@redhat.com> In-Reply-To: <20120410133708.GE21801@redhat.com> X-Enigmail-Version: 1.4 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2012-04-10 15:37, Vivek Goyal wrote: > Hi, > > I am wondering if CFQ as default scheduler is still the right choice. CFQ > generally works well on slow rotational media (SATA?). But often > underperforms on faster storage (storage arrays, PCIE SSDs, virtualized > disk in linux guests etc). People often put logic in user space to tune their > systems and change IO scheduler to deadline to get better performance on > faster storage. > > Though there is not one good answer for all kind of storage and for all > kind of workloads, I am wondering if we can provide a better default and > that is change default IO scheduler to "deadline" except SATA. > > One can argue that some SAS disks can be slow too and benefit from CFQ. Yes, > but default IO scheduler choice is not perfect anyway. It just tries to > cater to a wide variety of use cases out of the box. > > So I am throwing this patch out see if it flies. Personally, I think it > might turn out to be a more reasonable default. I think it'd be a lot more sane to just use CFQ on rotational single devices, and default to deadline on raid or non-rotational devices. This still isn't perfect, since less worthy SSDs still benefit from the read/write separation, and some multi device configs will be faster as well. But it's better. The below patch is not a good idea. There's no clear distinction between on what CFQ is now the default. -- Jens Axboe