[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?
