linux-kernel - Re: [PATCH 1/4] bitops: Add single_bit

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Date:   Tue, 23 Nov 2021 10:10:46 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Yury Norov <yury.norov@...il.com>,
        "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        Matti Vaittinen <mazziesaccount@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jiri Kosina <trivial@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] bitops: Add single_bit_set()

Hi Andy,

On Tue, Nov 23, 2021 at 10:04 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> Be sure you get better assembly in these cases. As I have told already,
> hweight() is a single assembly instruction, I'm not sure open coded variant

... on a select set of architectures.

Do we need CONFIG_HAVE_FAST_HWEIGHT?

> may be better even for long bitmaps. That said, assembly comparison and
> some performance tests would be nice to have.

> As an API per se it might make sense to have such, but you know that we don't
> add it without users.

Indeed. And code for unused APIs increase kernel size, too
(without LTO).

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds