Re: [PATCH V9 09/15] mmc: core: Add parameter use_blk_mq

From	Adrian Hunter <adrian.hunter@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH V9 09/15] mmc: core: Add parameter use_blk_mq
Date	2017-09-27 14:10 +0200
Message-ID	<uujk5-2b5-5@gated-at.bofh.it> (permalink)
References	<usvz3-68T-3@gated-at.bofh.it> <usvz4-68T-17@gated-at.bofh.it> <uu7LY-2Wl-3@gated-at.bofh.it>
Organization	Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki

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On 27/09/17 02:42, Linus Walleij wrote:
> On Fri, Sep 22, 2017 at 2:36 PM, Adrian Hunter <adrian.hunter@intel.com> wrote:
> 
>> Until mmc has blk-mq support fully implemented and tested, add a
>> parameter use_blk_mq, default to false unless config option MMC_MQ_DEFAULT
>> is selected.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> 
>> +config MMC_MQ_DEFAULT
>> +       bool "MMC: use blk-mq I/O path by default"
>> +       depends on MMC && BLOCK
> 
> I would say:
> default y
> 
> Why not. SCSI is starting to enable this by default so IMO we should

SCSI didn't manage it yet.

> not take the
> intermediate step of having this as optional. Otherwise it never gets tested.

The argument that we don't have to take any responsibility for getting
things tested is a poor one.

Anyway, you can always send a patch later to change the default, so why the
hurry to do it now?

> 
> Set it to default y and after two kernel releases, if nothing happens, we simply
> delete the old block layer path.
> 
>> +#ifdef CONFIG_MMC_MQ_DEFAULT
>> +bool mmc_use_blk_mq = true;
>> +#else
>> +bool mmc_use_blk_mq = false;
>> +#endif
>> +module_param_named(use_blk_mq, mmc_use_blk_mq, bool, S_IWUSR | S_IRUGO);
> 
> Are people really modprobing this so it needs to be a module parameter?

Irrespective of modprobe, the parameter can be changed without re-compiling.

> 
> Maybe I'm the only developer stupid enough to just recompile and reboot

Just change the parameter and unbind and rebind the host controller.

Thread

Re: [PATCH V9 09/15] mmc: core: Add parameter use_blk_mq Linus Walleij <linus.walleij@linaro.org> - 2017-09-27 01:50 +0200
  Re: [PATCH V9 09/15] mmc: core: Add parameter use_blk_mq Adrian Hunter <adrian.hunter@intel.com> - 2017-09-27 14:10 +0200
    Re: [PATCH V9 09/15] mmc: core: Add parameter use_blk_mq Linus Walleij <linus.walleij@linaro.org> - 2017-09-27 21:50 +0200
  RE: [PATCH V9 09/15] mmc: core: Add parameter use_blk_mq Avri Altman <Avri.Altman@wdc.com> - 2017-09-27 15:00 +0200

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