linux-kernel - Re: [PATCH V8 08/14] mmc: core: Add parameter use_blk

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Message-ID: <CACRpkdbQU3V3SGH6dgOZU41W-384=GYw-pY=A6AnUY1MNWEKUA@mail.gmail.com>
Date:   Fri, 22 Sep 2017 16:01:54 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Bough Chen <haibo.chen@....com>,
        Alex Lemberg <alex.lemberg@...disk.com>,
        Mateusz Nowak <mateusz.nowak@...el.com>,
        Yuliy Izrailov <Yuliy.Izrailov@...disk.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Dong Aisheng <dongas86@...il.com>,
        Das Asutosh <asutoshd@...eaurora.org>,
        Zhangfei Gao <zhangfei.gao@...il.com>,
        Sahitya Tummala <stummala@...eaurora.org>,
        Harjani Ritesh <riteshh@...eaurora.org>,
        Venu Byravarasu <vbyravarasu@...dia.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V8 08/14] mmc: core: Add parameter use_blk_mq

On Fri, Sep 22, 2017 at 3:30 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:
> On 21/09/17 12:47, Ulf Hansson wrote:

>> I asume the goal of adding this option is to enable us to move slowly
>> forward. In general that might be a good idea, however for this
>> particular case I am not sure.
>>
>> The main reason is simply that I find it unlikely that people and
>> distributions will actually go in and change the default value, so in
>> the end we will just be adding new code, which isn't really going to
>> be much tested. That's what happened in scsi case.
>
> The argument that no one is going to test anyway so we shouldn't give them
> the opportunity, is not a sustainable vision for the future.  Instead we
> should reach out to relevant stakeholders and get them to do their testing
> with blk-mq first.

We *could* simply invert the option then. Default it to "y" and
only leave it as a debugging aid so that people can set it to
"n" if they want to test with MQ disabled.

This is also simple to revert by a oneliner just removing "default y"
if there are problems with it.

Yours,
Linus Walleij