user/sven/linux.git/include/linux/bitops.h, branch v6.12.55

bitops: Add a comment explaining the double underscore macros

2024-06-18T17:40:53Z

Linus Walleij pointed out that a new comer might be confused about the difference between set_bit() and __set_bit(). Add a comment explaining the difference. Link: https://lore.kernel.org/all/CACRpkdZFPG_YLici-BmYfk9HZ36f4WavCN3JNotkk8cPgCODCg@mail.gmail.com/ Signed-off-by: Dan Carpenter Reviewed-by: Linus Walleij Signed-off-by: Yury Norov

Merge tag 'bitmap-for-6.10v2' of https://github.com/norov/linux

2024-05-21T22:29:01Z

Pull bitmap updates from Yury Norov: - topology_span_sane() optimization from Kyle Meyer - fns() rework from Kuan-Wei Chiu (used in cpumask_local_spread() and other places) - headers cleanup from Andy - add a MAINTAINERS record for bitops API * tag 'bitmap-for-6.10v2' of https://github.com/norov/linux: usercopy: Don't use "proxy" headers bitops: Move aligned_byte_mask() to wordpart.h MAINTAINERS: add BITOPS API record bitmap: relax find_nth_bit() limitation on return value lib: make test_bitops compilable into the kernel image bitops: Optimize fns() for improved performance lib/test_bitops: Add benchmark test for fns() Compiler Attributes: Add __always_used macro sched/topology: Optimize topology_span_sane() cpumask: Add for_each_cpu_from()

Merge tag 'asm-generic-6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic

2024-05-20T22:18:34Z

Pull asm-generic cleanups from Arnd Bergmann: "These are a few cross-architecture cleanup patches: - separate out fbdev support from the asm/video.h contents that may be used by either the old fbdev drivers or the newer drm display code (Thomas Zimmermann) - cleanups for the generic bitops code and asm-generic/bug.h (Thorsten Blum) - remove the orphaned include/asm-generic/page.h header that used to be included by long-removed mmu-less architectures (me)" * tag 'asm-generic-6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic: arch: Fix name collision with ACPI's video.o bug: Improve comment asm-generic: remove unused asm-generic/page.h arch: Rename fbdev header and source files arch: Remove struct fb_info from video helpers arch: Select fbdev helpers with CONFIG_VIDEO bitops: Change function return types from long to int

bitops: Move aligned_byte_mask() to wordpart.h

2024-05-19T23:12:38Z

The bitops.h is for bit related operations. The aligned_byte_mask() is about byte (or part of the machine word) operations, for which we have a separate header, move the mentioned macro to wordpart.h to consolidate similar operations. Signed-off-by: Andy Shevchenko Signed-off-by: Yury Norov

bitops: Optimize fns() for improved performance

2024-05-09T16:25:08Z

The current fns() repeatedly uses __ffs() to find the index of the least significant bit and then clears the corresponding bit using __clear_bit(). The method for clearing the least significant bit can be optimized by using word &= word - 1 instead. Typically, the execution time of one __ffs() plus one __clear_bit() is longer than that of a bitwise AND operation and a subtraction. To improve performance, the loop for clearing the least significant bit has been replaced with word &= word - 1, followed by a single __ffs() operation to obtain the answer. This change reduces the number of __ffs() iterations from n to just one, enhancing overall performance. This modification significantly accelerates the fns() function in the test_bitops benchmark, improving its speed by approximately 7.6 times. Additionally, it enhances the performance of find_nth_bit() in the find_bit benchmark by approximately 26%. Before: test_bitops: fns: 58033164 ns find_nth_bit: 4254313 ns, 16525 iterations After: test_bitops: fns: 7637268 ns find_nth_bit: 3362863 ns, 16501 iterations CC: Andrew Morton CC: Rasmus Villemoes Signed-off-by: Kuan-Wei Chiu Signed-off-by: Yury Norov

bitops: Change function return types from long to int

2024-05-03T15:04:50Z

Change the return types of bitops functions (ffs, fls, and fns) from long to int. The expected return values are in the range [0, 64], for which int is sufficient. Additionally, int aligns well with the return types of the corresponding __builtin_* functions, potentially reducing overall type conversions. Many of the existing bitops functions already return an int and don't need to be changed. The bitops functions in arch/ should be considered separately. Adjust some return variables to match the function return types. With GCC 13 and defconfig, these changes reduced the size of a test kernel image by 5,432 bytes on arm64 and by 248 bytes on riscv; there were no changes in size on x86_64, powerpc, or m68k. Signed-off-by: Thorsten Blum Signed-off-by: Arnd Bergmann

bitops: let the compiler optimize {__,}assign_bit()

2024-04-01T09:49:27Z

Since commit b03fc1173c0c ("bitops: let optimize out non-atomic bitops on compile-time constants"), the compilers are able to expand inline bitmap operations to compile-time initializers when possible. However, during the round of replacement if-__set-else-__clear with __assign_bit() as per Andy's advice, bloat-o-meter showed +1024 bytes difference in object code size for one module (even one function), where the pattern: DECLARE_BITMAP(foo) = { }; // on the stack, zeroed if (a) __set_bit(const_bit_num, foo); if (b) __set_bit(another_const_bit_num, foo); ... is heavily used, although there should be no difference: the bitmap is zeroed, so the second half of __assign_bit() should be compiled-out as a no-op. I either missed the fact that __assign_bit() has bitmap pointer marked as `volatile` (as we usually do for bitops) or was hoping that the compilers would at least try to look past the `volatile` for __always_inline functions. Anyhow, due to that attribute, the compilers were always compiling the whole expression and no mentioned compile-time optimizations were working. Convert __assign_bit() to a macro since it's a very simple if-else and all of the checks are performed inside __set_bit() and __clear_bit(), thus that wrapper has to be as transparent as possible. After that change, despite it showing only -20 bytes change for vmlinux (due to that it's still relatively unpopular), no drastic code size changes happen when replacing if-set-else-clear for onstack bitmaps with __assign_bit(), meaning the compiler now expands them to the actual operations will all the expected optimizations. Atomic assign_bit() is less affected due to its nature, but let's convert it to a macro as well to keep the code consistent and not leave a place for possible suboptimal codegen. Moreover, with certain kernel configuration it actually gives some saves (x86): do_ip_setsockopt 4154 4099 -55 Suggested-by: Yury Norov # assign_bit(), too Cc: Andy Shevchenko Reviewed-by: Przemek Kitszel Acked-by: Yury Norov Signed-off-by: Alexander Lobakin Signed-off-by: David S. Miller

bitops: make BYTES_TO_BITS() treewide-available

2024-04-01T09:49:27Z

Avoid open-coding that simple expression each time by moving BYTES_TO_BITS() from the probes code to to export it to the rest of the kernel. Simplify the macro while at it. `BITS_PER_LONG / sizeof(long)` always equals to %BITS_PER_BYTE, regardless of the target architecture. Do the same for the tools ecosystem as well (incl. its version of bitops.h). The previous implementation had its implicit type of long, while the new one is int, so adjust the format literal accordingly in the perf code. Suggested-by: Andy Shevchenko Reviewed-by: Przemek Kitszel Acked-by: Yury Norov Signed-off-by: Alexander Lobakin Signed-off-by: David S. Miller

bitops: add missing prototype check

2024-04-01T09:49:27Z

Commit 8238b4579866 ("wait_on_bit: add an acquire memory barrier") added a new bitop, test_bit_acquire(), with proper wrapping in order to try to optimize it at compile-time, but missed the list of bitops used for checking their prototypes a bit below. The functions added have consistent prototypes, so that no more changes are required and no functional changes take place. Fixes: 8238b4579866 ("wait_on_bit: add an acquire memory barrier") Reviewed-by: Przemek Kitszel Signed-off-by: Alexander Lobakin Signed-off-by: David S. Miller

Merge tag 'mm-nonmm-stable-2022-10-11' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2022-10-12T18:00:22Z

Pull non-MM updates from Andrew Morton: - hfs and hfsplus kmap API modernization (Fabio Francesco) - make crash-kexec work properly when invoked from an NMI-time panic (Valentin Schneider) - ntfs bugfixes (Hawkins Jiawei) - improve IPC msg scalability by replacing atomic_t's with percpu counters (Jiebin Sun) - nilfs2 cleanups (Minghao Chi) - lots of other single patches all over the tree! * tag 'mm-nonmm-stable-2022-10-11' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (71 commits) include/linux/entry-common.h: remove has_signal comment of arch_do_signal_or_restart() prototype proc: test how it holds up with mapping'less process mailmap: update Frank Rowand email address ia64: mca: use strscpy() is more robust and safer init/Kconfig: fix unmet direct dependencies ia64: update config files nilfs2: replace WARN_ONs by nilfs_error for checkpoint acquisition failure fork: remove duplicate included header files init/main.c: remove unnecessary (void*) conversions proc: mark more files as permanent nilfs2: remove the unneeded result variable nilfs2: delete unnecessary checks before brelse() checkpatch: warn for non-standard fixes tag style usr/gen_init_cpio.c: remove unnecessary -1 values from int file ipc/msg: mitigate the lock contention with percpu counter percpu: add percpu_counter_add_local and percpu_counter_sub_local fs/ocfs2: fix repeated words in comments relay: use kvcalloc to alloc page array in relay_alloc_page_array proc: make config PROC_CHILDREN depend on PROC_FS fs: uninline inode_maybe_inc_iversion() ...