On Mon, Feb 15, 2021 at 01:30:44PM -0800, Yury Norov wrote:
[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.
Because tools are user space programs and sometimes may not follow kernel
specifics, so they are different logically and changes should be separated.
Anything else?
--
With Best Regards,
Andy Shevchenko
