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

[Adrian Hunter]

On 27/09/17 02:42, Linus Walleij wrote:
> On Fri, Sep 22, 2017 at 2:36 PM, Adrian Hunter <adrian.hunter@xxxxxxxxx> 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@xxxxxxxxx>
> 
>> +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.