[PATCH 0/4] bitops: optimize fns() for more

From: Yury Norov
Date: Thu May 02 2024 - 19:32:18 EST


This series follows up [1].

[1] improves performance by switching from __ffs() + __clear_bit()
in fns() to the equivalent but much faster expression that searches
and clears first N-1 bits:

while (word && n--)
word &= word - 1;

We can squeeze out of fns() even more by replacing linear walk over all
the bits in a word with a binary search.

Patch #3 implements it by adding fns8(), fns16(), fns32() and fns64(),
and patches 1 and 2 are cleanups related to fns().

The last patch creates a MAINTAINERS record for bitops. Currently they
aren't maintained. I add Rasmus and myself as a reviewer and maintainer,
accordingly, just like for bitmaps. Rasmus, please let me know if you
don't want to review it.

[1] https://lore.kernel.org/linux-kernel/20240502092443.6845-2-visitorckw@xxxxxxxxx/T/

Yury Norov (4):
lib: make test_bitops compilable into the kernel image
bitmap: relax find_nth_bit() limitation on return value
bitops: squeeze even more out of fns()
MAINTAINERS: add BITOPS API record

MAINTAINERS | 13 +++++++++++++
include/linux/bitops.h | 42 +++++++++++++++++++++++++++++++++++++-----
include/linux/find.h | 2 +-
lib/Kconfig.debug | 1 -
lib/find_bit.c | 2 +-
lib/test_bitmap.c | 4 ++--
6 files changed, 54 insertions(+), 10 deletions(-)

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2.40.1