[RESEND PATCH v2 0/6] lib/find_bit: fast path for small bitmaps

Yury Norov
2021-01-30T19:18:16Z

Bitmap operations are much simpler and faster in case of small bitmaps
which 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 are small and their size is known at
compile time.

find_*_bit() API lacks this functionality; despite users will benefit from
it a lot. One important example is cpumask subsystem when
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.

Tools is synchronized with new implementation where needed.

v1: https://www.spinics.net/lists/kernel/msg3804727.html
v2: - employ GENMASK() for bitmaps;
- unify find_bit inliners in;
- address comments to v1;

Yury Norov (8):
tools: disable -Wno-type-limits
tools: bitmap: sync function declarations with linux kernel
arch: rearrange headers inclusion order in asm/bitops for m68k and sh
lib: introduce BITS_{FIRST,LAST} macro
bitsperlong.h: introduce SMALL_CONST() macro
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 | 108 +++++++++++++++++++++---
include/asm-generic/bitops/le.h | 38 ++++++++-
include/asm-generic/bitsperlong.h | 2 +
include/linux/bitmap.h | 60 ++++++-------
include/linux/bitops.h | 12 ---
include/linux/bits.h | 6 ++
include/linux/cpumask.h | 8 +-
include/linux/netdev_features.h | 2 +-
include/linux/nodemask.h | 2 +-
lib/bitmap.c | 26 +++---
lib/find_bit.c | 72 +++-------------
lib/genalloc.c | 8 +-
tools/include/asm-generic/bitops/find.h | 85 +++++++++++++++++--
tools/include/asm-generic/bitsperlong.h | 2 +
tools/include/linux/bitmap.h | 47 ++++-------
tools/include/linux/bits.h | 6 ++
tools/lib/bitmap.c | 10 +--
tools/lib/find_bit.c | 56 +++++-------
tools/scripts/Makefile.include | 1 +
tools/testing/radix-tree/bitmap.c | 4 +-
22 files changed, 337 insertions(+), 225 deletions(-)

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2.25.1