[0/6] lib/find_bit: fast path for small bitmaps

Message

Yury Norov Jan. 21, 2021, 12:06 a.m. UTC

Bitmap operations are much simpler and faster in case of small bitmaps,
whicn fit into a single word. In linux/bitmap.h we have a machinery that
allows compiler to replace actual function call with a few instructions
if bitmaps passed into the function is small and its size is known at
compile time.

find_next_*_bit() lacks this functionality; despite users will
benefit from it a lot. One important example is cpumask subsystem if
NR_CPUS <= BITS_PER_LONG. In the very best case, the compiler may replace
a find_*_bit() call for such a bitmap with a single ffs or ffz instruction.

Yury Norov (6):
  arch: rearrahge headers inclusion order in asm/bitops for m68k and sh
  bitmap: move some macros from linux/bitmap.h to linux/bitops.h
  tools: sync bitops macro definitions with the kernel
  lib: inline _find_next_bit() wrappers
  lib: add fast path for find_next_*_bit()
  lib: add fast path for find_first_*_bit() and find_last_bit()

 arch/m68k/include/asm/bitops.h    |   4 +-
 arch/sh/include/asm/bitops.h      |   3 +-
 include/asm-generic/bitops/find.h | 123 +++++++++++++++++++++++++++---
 include/asm-generic/bitops/le.h   |  45 ++++++++++-
 include/linux/bitmap.h            |  11 ---
 include/linux/bitops.h            |  23 +++---
 lib/find_bit.c                    |  68 ++---------------
 tools/include/linux/bitmap.h      |  11 ---
 tools/include/linux/bitops.h      |  11 +++
 9 files changed, 188 insertions(+), 111 deletions(-)