Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752043AbdHCKsC (ORCPT ); Thu, 3 Aug 2017 06:48:02 -0400 Received: from outbound-smtp05.blacknight.com ([81.17.249.38]:43457 "EHLO outbound-smtp05.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751755AbdHCKsB (ORCPT ); Thu, 3 Aug 2017 06:48:01 -0400 Date: Thu, 3 Aug 2017 11:47:59 +0100 From: Mel Gorman To: Ming Lei Cc: Christoph Hellwig , Jens Axboe , Linux Kernel Mailing List , linux-block , Paolo Valente Subject: Re: Switching to MQ by default may generate some bug reports Message-ID: <20170803104759.h2e5ubgh3zk2ucco@techsingularity.net> References: <20170803085115.r2jfz2lofy5spfdb@techsingularity.net> <20170803094242.wol67mmga3om4gjp@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170421 (1.8.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1585 Lines: 37 On Thu, Aug 03, 2017 at 05:57:50PM +0800, Ming Lei wrote: > On Thu, Aug 3, 2017 at 5:42 PM, Mel Gorman wrote: > > On Thu, Aug 03, 2017 at 05:17:21PM +0800, Ming Lei wrote: > >> Hi Mel Gorman, > >> > >> On Thu, Aug 3, 2017 at 4:51 PM, Mel Gorman wrote: > >> > Hi Christoph, > >> > > >> > I know the reasons for switching to MQ by default but just be aware that it's > >> > not without hazards albeit it the biggest issues I've seen are switching > >> > CFQ to BFQ. On my home grid, there is some experimental automatic testing > >> > running every few weeks searching for regressions. Yesterday, it noticed > >> > that creating some work files for a postgres simulator called pgioperf > >> > was 38.33% slower and it auto-bisected to the switch to MQ. This is just > >> > linearly writing two files for testing on another benchmark and is not > >> > remarkable. The relevant part of the report is > >> > >> We saw some SCSI-MQ performance issue too, please see if the following > >> patchset fixes your issue: > >> > >> http://marc.info/?l=linux-block&m=150151989915776&w=2 > >> > > > > That series is dealing with problems with legacy-deadline vs mq-none where > > as the bulk of the problems reported in this mail are related to > > legacy-CFQ vs mq-BFQ. > > The serials deals with none and all mq schedulers, and you can see > the improvement on mq-deadline in cover letter, :-) > Would it be expected to fix a 2x to 4x slowdown as experienced by BFQ that was not observed on other schedulers? -- Mel Gorman SUSE Labs