linux-kernel - Re: drivers: Inline code in devm_platform_ioremap

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Date:   Tue, 18 Jun 2019 13:44:11 +0200
From:   Markus Elfring <Markus.Elfring@....de>
To:     Enrico Weigelt <lkml@...ux.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     cocci@...teme.lip6.fr, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Himanshu Jha <himanshujha199640@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nicolas Palix <nicolas.palix@...g.fr>
Subject: Re: drivers: Inline code in devm_platform_ioremap_resource() from two
 functions

>> Would you like to check the software circumstances once more
>> for the generation of a similar code structure by a C compiler
>> (or optimiser)?
>
> As said: unfortunately, I don't have the time to do that

I became curious if you would like to adjust your software development
attention a bit more also in this area.


> - you'd have to tell us, what exactly you've got in mind.

I try to point possibilities out to improve the combination of
two functions.


> If it's just about some error checks which happen to be redundant in a
> particular case, you'll have to show that this case is a *really* hot
> path (eg. irq, syscall, scheduling, etc) - but I don't see that here.

1. May the check “resource_type(res) == IORESOURCE_MEM” be performed
   in a local loop?

2. How hot do you find the null pointer check for the device
   input parameter of the function “devm_ioremap_resource”?


> Any actual measurements on how your patch improves that ?

Not yet. - Which benchmarks would you trust here?


> Look, I understand that you'd like to squeeze out maximum performance,

I hope so.


> but this has to be practically maintainable.

This can be achieved if more contributors would find proposed
adjustments helpful for another software transformation.

Regards,
Markus