From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 3 Aug 2017 10:42:43 +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: <20170803094242.wol67mmga3om4gjp@techsingularity.net> References: <20170803085115.r2jfz2lofy5spfdb@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 In-Reply-To: List-ID: 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. -- Mel Gorman SUSE Labs