linux-kernel - Re: Switching to MQ by default may generate some bug reports

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Message-Id: <DAC70C00-B51D-4752-8EA7-EA55368918EC@linaro.org>
Date:   Thu, 3 Aug 2017 11:44:06 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Ming Lei <tom.leiming@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>
Subject: Re: Switching to MQ by default may generate some bug reports


> Il giorno 03 ago 2017, alle ore 11:42, Mel Gorman <mgorman@...hsingularity.net> ha scritto:
> 
> 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 <mgorman@...hsingularity.net> 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.
> 

Out-of-curiosity: you get no regression with mq-none or mq-deadline?

Thanks,
Paolo

> -- 
> Mel Gorman
> SUSE Labs