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Date:   Wed, 2 Dec 2020 20:51:27 +0200
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Yun Levi <ppbuk5246@gmail.com>
Cc:     Yury Norov <yury.norov@gmail.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>, dushistov@mail.ru,
        Arnd Bergmann <arnd@arndb.de>,
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On Thu, Dec 03, 2020 at 03:27:33AM +0900, Yun Levi wrote:
> On Thu, Dec 3, 2020 at 2:36 AM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Wed, Dec 02, 2020 at 09:26:05AM -0800, Yury Norov wrote:

...

> > Side note: speaking of performance, any plans to fix for_each_*_bit*() for
> > cases when the nbits is known to be <= BITS_PER_LONG?
> >
> > Now it makes an awful code generation (something like few hundred bytes of
> > code).

> Frankly Speaking, I don't have an idea in now.....
> Could you share your idea or wisdom?

Something like (I may be mistaken by names, etc, I'm not a compiler expert,
and this is in pseudo language, I don't remember all API names by hart,
just to express the idea) as a rough first step

__builtin_constant(nbits, find_next_set_bit_long, find_next_set_bit)

find_next_set_bit_long()
{
	unsigned long v = BIT_LAST_WORD(i);
	return ffs_long(v);
}

Same for find_first_set_bit() -> map it to ffs_long().

And I believe it can be optimized more.

-- 
With Best Regards,
Andy Shevchenko