Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754531AbcJZPck (ORCPT ); Wed, 26 Oct 2016 11:32:40 -0400 Received: from mail-it0-f42.google.com ([209.85.214.42]:37356 "EHLO mail-it0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750857AbcJZPcj (ORCPT ); Wed, 26 Oct 2016 11:32:39 -0400 Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler To: Christoph Hellwig , Arnd Bergmann References: <1477474082-2846-1-git-send-email-paolo.valente@linaro.org> <20161026113443.GA13587@quack2.suse.cz> <4ed3e291-b3e5-5ee3-6838-58644bd3d99b@sandisk.com> <12386463.fJy0cVexVD@wuerfel> <20161026152955.GA21262@infradead.org> Cc: Bart Van Assche , Jan Kara , Paolo Valente , Tejun Heo , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, broonie@kernel.org, hare@suse.de, grant.likely@secretlab.ca, James.Bottomley@hansenpartnership.com From: Jens Axboe Message-ID: <3ebadbb8-9ac2-851a-66f9-c9db25713695@kernel.dk> Date: Wed, 26 Oct 2016 09:32:36 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20161026152955.GA21262@infradead.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1073 Lines: 23 On 10/26/2016 09:29 AM, Christoph Hellwig wrote: > On Wed, Oct 26, 2016 at 05:13:07PM +0200, Arnd Bergmann wrote: >> The question to ask first is whether to actually have pluggable >> schedulers on blk-mq at all, or just have one that is meant to >> do the right thing in every case (and possibly can be bypassed >> completely). > > That would be my preference. Have a BFQ-variant for blk-mq as an > option (default to off unless opted in by the driver or user), and > not other scheduler for blk-mq. Don't bother with bfq for non > blk-mq. It's not like there is any advantage in the legacy-request > device even for slow devices, except for the option of having I/O > scheduling. It's the only right way forward. blk-mq might not offer any substantial advantages to rotating storage, but with scheduling, it won't offer a downside either. And it'll take us towards the real goal, which is to have just one IO path. Adding a new scheduler for the legacy IO path makes no sense. Adding one for blk-mq and phasing out the old path is what we need to do. -- Jens Axboe