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

[Yury Norov]

[add David Laight <David.Laight@xxxxxxxxxx> ]

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?