linux-kernel - Re: [PATCH v2 09/13] bitmap: make bitmap_{get,set}_value8() use bitmap

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Message-ID: <ZS13Z8Ls69lEBYib@yury-ThinkPad>
Date:   Mon, 16 Oct 2023 10:48:23 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Alexander Potapenko <glider@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        David Ahern <dsahern@...nel.org>,
        Przemek Kitszel <przemyslaw.kitszel@...el.com>,
        Simon Horman <simon.horman@...igine.com>,
        netdev@...r.kernel.org, linux-btrfs@...r.kernel.org,
        dm-devel@...hat.com, ntfs3@...ts.linux.dev,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/13] bitmap: make bitmap_{get,set}_value8() use
 bitmap_{read,write}()

On Mon, Oct 16, 2023 at 06:52:43PM +0200, Alexander Lobakin wrote:
> Now that we have generic bitmap_read() and bitmap_write(), which are
> inline and try to take care of non-bound-crossing and aligned cases
> to keep them optimized, collapse bitmap_{get,set}_value8() into
> simple wrappers around the former ones.
> bloat-o-meter shows no difference in vmlinux and -2 bytes for
> gpio-pca953x.ko, which says the code doesn't get optimized worse.

That's just amazing!

bloat-o-meter itself doesn't say on optimization, but in this case
I think that BITS_PER_BYTE passed at compile time allows to generate
just as good code with the generic bitmap_write/read().

Acked-by: Yury Norov <yury.norov@...il.com>

> Suggested-by: Yury Norov <yury.norov@...il.com>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> ---
>  include/linux/bitmap.h | 38 +++++---------------------------------
>  1 file changed, 5 insertions(+), 33 deletions(-)
> 
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> index 2020cb534ed7..c2680f67bc4e 100644
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -572,39 +572,6 @@ static inline void bitmap_from_u64(unsigned long *dst, u64 mask)
>  	bitmap_from_arr64(dst, &mask, 64);
>  }
>  
> -/**
> - * bitmap_get_value8 - get an 8-bit value within a memory region
> - * @map: address to the bitmap memory region
> - * @start: bit offset of the 8-bit value; must be a multiple of 8
> - *
> - * Returns the 8-bit value located at the @start bit offset within the @src
> - * memory region.
> - */
> -static inline unsigned long bitmap_get_value8(const unsigned long *map,
> -					      unsigned long start)
> -{
> -	const size_t index = BIT_WORD(start);
> -	const unsigned long offset = start % BITS_PER_LONG;
> -
> -	return (map[index] >> offset) & 0xFF;
> -}
> -
> -/**
> - * bitmap_set_value8 - set an 8-bit value within a memory region
> - * @map: address to the bitmap memory region
> - * @value: the 8-bit value; values wider than 8 bits may clobber bitmap
> - * @start: bit offset of the 8-bit value; must be a multiple of 8
> - */
> -static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
> -				     unsigned long start)
> -{
> -	const size_t index = BIT_WORD(start);
> -	const unsigned long offset = start % BITS_PER_LONG;
> -
> -	map[index] &= ~(0xFFUL << offset);
> -	map[index] |= value << offset;
> -}
> -
>  /**
>   * bitmap_read - read a value of n-bits from the memory region
>   * @map: address to the bitmap memory region
> @@ -676,6 +643,11 @@ static inline void bitmap_write(unsigned long *map,
>  	map[index + 1] |= (value >> space);
>  }
>  
> +#define bitmap_get_value8(map, start)			\
> +	bitmap_read(map, start, BITS_PER_BYTE)
> +#define bitmap_set_value8(map, value, start)		\
> +	bitmap_write(map, value, start, BITS_PER_BYTE)
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* __LINUX_BITMAP_H */
> -- 
> 2.41.0