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

[add David Laight [off-list ref] ]

On Sat, Jan 30, 2021 at 11:17:11AM -0800, Yury Norov wrote:

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;

Comments so far:
 - increased image size (patch #8) - addressed by introducing
   CONFIG_FAST_PATH;
 - split tools and kernel parts - not clear why it's better.

 Anything else?