linux-kernel - Re: [PATCH v13 01/11] bitops: Introduce the for_each_set

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Message-ID: <20190328073049.jpizz6uio7er2sjv@wunner.de>
Date:   Thu, 28 Mar 2019 08:30:49 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     linus.walleij@...aro.org, bgolaszewski@...libre.com,
        akpm@...ux-foundation.org, linux-gpio@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        andriy.shevchenko@...ux.intel.com, linux@...musvillemoes.dk,
        yamada.masahiro@...ionext.com,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        geert@...ux-m68k.org, preid@...ctromag.com.au,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v13 01/11] bitops: Introduce the for_each_set_clump8 macro

On Thu, Mar 28, 2019 at 01:30:13PM +0900, William Breathitt Gray wrote:
> On Wed, Mar 27, 2019 at 07:42:54AM +0100, Lukas Wunner wrote:
> > On Wed, Mar 27, 2019 at 01:58:45PM +0900, William Breathitt Gray wrote:
> > > This macro iterates for each 8-bit group of bits (clump) with set bits,
> > > within a bitmap memory region. For each iteration, "start" is set to the
> > > bit offset of the found clump, while the respective clump value is
> > > stored to the location pointed by "clump". Additionally, the
> > > bitmap_get_value8 and bitmap_set_value8 functions are introduced to
> > > respectively get and set an 8-bit value in a bitmap memory region.
> > 
> > I would have preferred static inlines for bitmap_get_value8(),
> > bitmap_set_value8() and find_next_clump8() to make this as fast
> > as possible in the callers because I've personally worked with
> > an industrial application where the GPIO pins of a 74x164 are
> > written every 250 usec.
> 
> I'm not sure these can be static inline since the symbols are exported
> for use outside this file.

By static inlines I meant that the functions are moved to the appropriate
header file in include/linux/.  You don't need to worry about exporting
in that case as the code is local to each module.  For smallish functions
like these, static inlines are usually fine.  See drivers/dma/virt-dma.h
for an extreme case of static inlines (as compared to the much smaller
virt-dma.c).

Thanks,

Lukas