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lib: extend the scope of small_const_nbits() macro

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find_bit would also benefit from small_const_nbits() optimizations.  The
detailed comment is provided by Rasmus Villemoes.

Link: https://lkml.kernel.org/r/20210401003153.97325-6-yury.norov@gmail.com
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Alexey Klimov <aklimov@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Sterba <dsterba@suse.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jianpeng Ma <jianpeng.ma@intel.com>
Cc: Joe Perches <joe@perches.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Stefano Brivio <sbrivio@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Yoshinori Sato <ysato@users.osdn.me>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Yury Norov 2021-05-06 18:02:56 -07:00 committed by Linus Torvalds
parent bb8bc36ef8
commit 586eaebea5
2 changed files with 12 additions and 8 deletions
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12
include/asm-generic/bitsperlong.h
View File

@ -23,4 +23,16 @@
#define BITS_PER_LONG_LONG 64
#endif
/*
* small_const_nbits(n) is true precisely when it is known at compile-time
* that BITMAP_SIZE(n) is 1, i.e. 1 <= n <= BITS_PER_LONG. This allows
* various bit/bitmap APIs to provide a fast inline implementation. Bitmaps
* of size 0 are very rare, and a compile-time-known-size 0 is most likely
* a sign of error. They will be handled correctly by the bit/bitmap APIs,
* but using the out-of-line functions, so that the inline implementations
* can unconditionally dereference the pointer(s).
*/
#define small_const_nbits(nbits) \
(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
#endif /* __ASM_GENERIC_BITS_PER_LONG */

8
include/linux/bitmap.h
View File

@ -223,14 +223,6 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf,
#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
/*
* The static inlines below do not handle constant nbits==0 correctly,
* so make such users (should any ever turn up) call the out-of-line
* versions.
*/
#define small_const_nbits(nbits) \
(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
{
unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);