linux-kernel - Re: [PATCH v6 00/12] lib/find_bit: fast path for small bitmaps

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Date:   Thu, 1 Apr 2021 12:14:12 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux-SH <linux-sh@...r.kernel.org>,
        Alexey Klimov <aklimov@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, David Sterba <dsterba@...e.com>,
        Dennis Zhou <dennis@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Jianpeng Ma <jianpeng.ma@...el.com>,
        Joe Perches <joe@...ches.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Rich Felker <dalias@...c.org>,
        Stefano Brivio <sbrivio@...hat.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH v6 00/12] lib/find_bit: fast path for small bitmaps

On Thu, Apr 1, 2021 at 3:36 AM Yury Norov <yury.norov@...il.com> wrote:
>
> Bitmap operations are much simpler and faster in case of small bitmaps
> which fit into a single word. In linux/bitmap.c we have a machinery that
> allows compiler to replace actual function call with a few instructions
> if bitmaps passed into the function are small and their size is known at
> compile time.
>
> find_*_bit() API lacks this functionality; but users will benefit from it
> a lot. One important example is cpumask subsystem when
> NR_CPUS <= BITS_PER_LONG.

Cool, thanks!

I guess it's assumed to go via Andrew's tree.

But after that since you are about to be a maintainer of this, I think
it would make sense to send PRs directly to Linus. I would recommend
creating an official tree (followed by an update in the MAINTAINERS)
and connecting it to Linux next (usually done by email to Stephen).


> v6 is mostly a resend. The only change comparing to v5 is a fix of
> small_const_nbits() synchronization patch.
>
> v1: https://www.spinics.net/lists/kernel/msg3804727.html
> v2: https://www.spinics.net/lists/linux-m68k/msg16945.html
> v3: https://www.spinics.net/lists/kernel/msg3837020.html
> v4: https://patchwork.kernel.org/project/linux-sh/cover/20210316015424.1999082-1-yury.norov@gmail.com/
> v5: https://lore.kernel.org/linux-arch/20210321215457.588554-1-yury.norov@gmail.com/T/
> v6: - sync small_const_nbits() properly (patch 6).
>     - Rasmus' ack added.
>
> Yury Norov (12):
>   tools: disable -Wno-type-limits
>   tools: bitmap: sync function declarations with the kernel
>   tools: sync BITMAP_LAST_WORD_MASK() macro with the kernel
>   arch: rearrange headers inclusion order in asm/bitops for m68k and sh
>   lib: extend the scope of small_const_nbits() macro
>   tools: sync small_const_nbits() macro with the kernel
>   lib: inline _find_next_bit() wrappers
>   tools: sync find_next_bit implementation
>   lib: add fast path for find_next_*_bit()
>   lib: add fast path for find_first_*_bit() and find_last_bit()
>   tools: sync lib/find_bit implementation
>   MAINTAINERS: Add entry for the bitmap API
>
>  MAINTAINERS                             |  16 ++++
>  arch/m68k/include/asm/bitops.h          |   6 +-
>  arch/sh/include/asm/bitops.h            |   5 +-
>  include/asm-generic/bitops/find.h       | 108 +++++++++++++++++++++---
>  include/asm-generic/bitops/le.h         |  38 ++++++++-
>  include/asm-generic/bitsperlong.h       |  12 +++
>  include/linux/bitmap.h                  |   8 --
>  include/linux/bitops.h                  |  12 ---
>  lib/find_bit.c                          |  68 ++-------------
>  tools/include/asm-generic/bitops/find.h |  85 +++++++++++++++++--
>  tools/include/asm-generic/bitsperlong.h |   3 +
>  tools/include/linux/bitmap.h            |  18 ++--
>  tools/lib/bitmap.c                      |   4 +-
>  tools/lib/find_bit.c                    |  56 +++++-------
>  tools/scripts/Makefile.include          |   1 +
>  15 files changed, 284 insertions(+), 156 deletions(-)
>
> --
> 2.25.1
>


--
With Best Regards,
Andy Shevchenko