mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-01-01 10:43:43 +00:00
Linux kernel source tree
3cea8d4753
Kernel lacks for a function that searches for Nth bit in a bitmap. Usually people do it like this: for_each_set_bit(bit, mask, size) if (n-- == 0) return bit; We can do it more efficiently, if we: 1. find a word containing Nth bit, using hweight(); and 2. find the bit, using a helper fns(), that works similarly to __ffs() and ffz(). fns() is implemented as a simple loop. For x86_64, there's PDEP instruction to do that: ret = clz(pdep(1 << idx, num)). However, for large bitmaps the most of improvement comes from using hweight(), so I kept fns() simple. New find_nth_bit() is ~70 times faster on x86_64/kvm in find_bit benchmark: find_nth_bit: 7154190 ns, 16411 iterations for_each_bit: 505493126 ns, 16315 iterations With all that, a family of 3 new functions is added, and used where appropriate in the following patches. Signed-off-by: Yury Norov <yury.norov@gmail.com> |
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.