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    SubjectRe: [PATCH 11/13] lib: add fast path for find_first_*_bit() and find_last_bit()
    On Mon, Mar 15, 2021 at 06:54:22PM -0700, Yury Norov wrote:
    > Similarly to bitmap functions, users would benefit if we'll handle
    > a case of small-size bitmaps that fit into a single word.
    >
    > While here, move the find_last_bit() declaration to bitops/find.h
    > where other find_*_bit() functions sit.
    >
    > Signed-off-by: Yury Norov <yury.norov@gmail.com>
    > ---
    > include/asm-generic/bitops/find.h | 50 ++++++++++++++++++++++++++++---
    > include/linux/bitops.h | 12 --------
    > lib/find_bit.c | 12 ++++----
    > 3 files changed, 52 insertions(+), 22 deletions(-)
    >
    > diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
    > index 4148c74a1e4d..8d818b304869 100644
    > --- a/include/asm-generic/bitops/find.h
    > +++ b/include/asm-generic/bitops/find.h
    > @@ -5,6 +5,9 @@
    > extern unsigned long _find_next_bit(const unsigned long *addr1,
    > const unsigned long *addr2, unsigned long nbits,
    > unsigned long start, unsigned long invert, unsigned long le);
    > +extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
    > +extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
    > +extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long size);
    >
    > #ifndef find_next_bit
    > /**
    > @@ -102,8 +105,17 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
    > * Returns the bit number of the first set bit.
    > * If no bits are set, returns @size.
    > */
    > -extern unsigned long find_first_bit(const unsigned long *addr,
    > - unsigned long size);
    > +static inline
    > +unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
    > +{
    > + if (small_const_nbits(size)) {
    > + unsigned long val = *addr & BITS_FIRST(size - 1);
    > +
    > + return val ? __ffs(val) : size;

    This patch results in:

    include/asm-generic/bitops/find.h: In function 'find_last_bit':
    include/asm-generic/bitops/find.h:164:16: error: implicit declaration of function '__fls'; did you mean '__ffs'?

    and:

    ./include/asm-generic/bitops/__fls.h: At top level:
    ./include/asm-generic/bitops/__fls.h:13:38: error: conflicting types for '__fls'

    when building scripts/mod/devicetable-offsets.o.

    Seen with h8300 builds.

    Guenter

    > + }
    > +
    > + return _find_first_bit(addr, size);
    > +}
    >
    > /**
    > * find_first_zero_bit - find the first cleared bit in a memory region
    > @@ -113,8 +125,17 @@ extern unsigned long find_first_bit(const unsigned long *addr,
    > * Returns the bit number of the first cleared bit.
    > * If no bits are zero, returns @size.
    > */
    > -extern unsigned long find_first_zero_bit(const unsigned long *addr,
    > - unsigned long size);
    > +static inline
    > +unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
    > +{
    > + if (small_const_nbits(size)) {
    > + unsigned long val = *addr | ~BITS_FIRST(size - 1);
    > +
    > + return val == ~0UL ? size : ffz(val);
    > + }
    > +
    > + return _find_first_zero_bit(addr, size);
    > +}
    > #else /* CONFIG_GENERIC_FIND_FIRST_BIT */
    >
    > #ifndef find_first_bit
    > @@ -126,6 +147,27 @@ extern unsigned long find_first_zero_bit(const unsigned long *addr,
    >
    > #endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
    >
    > +#ifndef find_last_bit
    > +/**
    > + * find_last_bit - find the last set bit in a memory region
    > + * @addr: The address to start the search at
    > + * @size: The number of bits to search
    > + *
    > + * Returns the bit number of the last set bit, or size.
    > + */
    > +static inline
    > +unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
    > +{
    > + if (small_const_nbits(size)) {
    > + unsigned long val = *addr & BITS_FIRST(size - 1);
    > +
    > + return val ? __fls(val) : size;
    > + }
    > +
    > + return _find_last_bit(addr, size);
    > +}
    > +#endif
    > +
    > /**
    > * find_next_clump8 - find next 8-bit clump with set bits in a memory region
    > * @clump: location to store copy of found clump
    > diff --git a/include/linux/bitops.h b/include/linux/bitops.h
    > index a5a48303b0f1..26bf15e6cd35 100644
    > --- a/include/linux/bitops.h
    > +++ b/include/linux/bitops.h
    > @@ -286,17 +286,5 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
    > })
    > #endif
    >
    > -#ifndef find_last_bit
    > -/**
    > - * find_last_bit - find the last set bit in a memory region
    > - * @addr: The address to start the search at
    > - * @size: The number of bits to search
    > - *
    > - * Returns the bit number of the last set bit, or size.
    > - */
    > -extern unsigned long find_last_bit(const unsigned long *addr,
    > - unsigned long size);
    > -#endif
    > -
    > #endif /* __KERNEL__ */
    > #endif
    > diff --git a/lib/find_bit.c b/lib/find_bit.c
    > index 2470ae390f3c..e2c301d28568 100644
    > --- a/lib/find_bit.c
    > +++ b/lib/find_bit.c
    > @@ -75,7 +75,7 @@ EXPORT_SYMBOL(_find_next_bit);
    > /*
    > * Find the first set bit in a memory region.
    > */
    > -unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
    > +unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
    > {
    > unsigned long idx;
    >
    > @@ -86,14 +86,14 @@ unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
    >
    > return size;
    > }
    > -EXPORT_SYMBOL(find_first_bit);
    > +EXPORT_SYMBOL(_find_first_bit);
    > #endif
    >
    > #ifndef find_first_zero_bit
    > /*
    > * Find the first cleared bit in a memory region.
    > */
    > -unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
    > +unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size)
    > {
    > unsigned long idx;
    >
    > @@ -104,11 +104,11 @@ unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
    >
    > return size;
    > }
    > -EXPORT_SYMBOL(find_first_zero_bit);
    > +EXPORT_SYMBOL(_find_first_zero_bit);
    > #endif
    >
    > #ifndef find_last_bit
    > -unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
    > +unsigned long _find_last_bit(const unsigned long *addr, unsigned long size)
    > {
    > if (size) {
    > unsigned long val = BITS_FIRST_MASK(size - 1);
    > @@ -124,7 +124,7 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
    > }
    > return size;
    > }
    > -EXPORT_SYMBOL(find_last_bit);
    > +EXPORT_SYMBOL(_find_last_bit);
    > #endif
    >
    > unsigned long find_next_clump8(unsigned long *clump, const unsigned long *addr,

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