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

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Date:   Thu, 3 Aug 2017 17:32:48 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     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>,
        Paolo Valente <paolo.valente@...aro.org>,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: Switching to MQ by default may generate some bug reports

On Thu, Aug 3, 2017 at 5:17 PM, Ming Lei <tom.leiming@...il.com> 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

BTW, the above patches(V1) can be found in the following tree:

      https://github.com/ming1/linux/commits/blk-mq-dispatch_for_scsi.V1

V2 has already been done but not posted out yet, because the performance test
on SRP isn't completed:

      https://github.com/ming1/linux/commits/blk-mq-dispatch_for_scsi.V2


Thanks,
Ming Lei