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

Andy Shevchenko
2021-04-01T09:15:28Z

On Thu, Apr 1, 2021 at 3:36 AM Yury Norov <yury.norov@gmail.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