On Tue, Feb 16, 2021 at 11:14:23AM +0200, Andy Shevchenko wrote:
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.
In this specific case tools follow kernel well.
Nevertheless, if you think it's a blocker for the series, I can split. What
option for tools is better for you - doubling the number of patches or
squashing everything in a patch bomb?
