Re: [PATCH v2] xen/lib: introduce generic find next bit operations

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

Hi Shawn,

Could you please take a look at the patch and PPC-related changes (
xen/arch/ppc/include/asm/bitops.h )?

Thanks in advance.

~ Oleksii

On Fri, 2024-02-09 at 18:58 +0100, Oleksii Kurochko wrote:
> find-next-bit.c is common for Arm64, PPC and RISCV64,
> so it is moved to xen/lib.
> 
> PPC has been transitioned to generic functions from find-next-bit.c
> since it now shares the same implementation as the PPC-specific code.
> 
> The MISRA exclude list has been updated to verify
> lib/find-next-bit.c instead of Arm's find_next_bit.c,
> as Arm's find_next_bit.c has been relocated to xen/lib/.
> 
> Despite CONFIG_GENERIC_FIND_FIRST_BIT not currently being used in
> Xen and being removed from the Linux kernel [1], it could
> theoretically
> prove useful for Xen. This is because the Linux kernel transitioned
> Arm to the generic version of find_first_bit() and
> find_first_zero_bit() due to improvements [1] in both performance
> and .text size.
> It would be prudent to investigate whether [1] is applicable to Xen
> as well and, if so, implement the necessary changes in a separate
> patch.
> 
> [1]
> https://lore.kernel.org/linux-arch/20211005054059.475634-5-yury.norov@xxxxxxxxx/
> 
> Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> ---
>  docs/misra/exclude-list.json                  |   8 +-
>  xen/arch/arm/arm64/lib/Makefile               |   2 +-
>  xen/arch/arm/include/asm/arm64/bitops.h       |  46 +------
>  xen/arch/ppc/include/asm/bitops.h             | 115 ----------------
> --
>  xen/include/xen/bitops.h                      |  48 ++++++++
>  xen/lib/Makefile                              |   1 +
>  .../find_next_bit.c => lib/find-next-bit.c}   |   0
>  7 files changed, 55 insertions(+), 165 deletions(-)
>  rename xen/{arch/arm/arm64/lib/find_next_bit.c => lib/find-next-
> bit.c} (100%)
> 
> diff --git a/docs/misra/exclude-list.json b/docs/misra/exclude-
> list.json
> index 7971d0e70f..b28174d0eb 100644
> --- a/docs/misra/exclude-list.json
> +++ b/docs/misra/exclude-list.json
> @@ -13,10 +13,6 @@
>              "rel_path": "arch/arm/arm64/insn.c",
>              "comment": "Imported on Linux, ignore for now"
>          },
> -        {
> -            "rel_path": "arch/arm/arm64/lib/find_next_bit.c",
> -            "comment": "Imported from Linux, ignore for now"
> -        },
>          {
>              "rel_path": "arch/x86/acpi/boot.c",
>              "comment": "Imported from Linux, ignore for now"
> @@ -221,6 +217,10 @@
>              "rel_path": "include/xen/decompress.h",
>              "comment": "Imported from Linux, ignore for now"
>          },
> +        {
> +            "rel_path": "lib/find-next-bit.c",
> +            "comment": "Imported from Linux, ignore for now"
> +        },
>          {
>              "rel_path": "lib/list-sort.c",
>              "comment": "Imported from Linux, ignore for now"
> diff --git a/xen/arch/arm/arm64/lib/Makefile
> b/xen/arch/arm/arm64/lib/Makefile
> index 1b9c7a95e6..66cfac435a 100644
> --- a/xen/arch/arm/arm64/lib/Makefile
> +++ b/xen/arch/arm/arm64/lib/Makefile
> @@ -1,4 +1,4 @@
>  obj-y += memcpy.o memcmp.o memmove.o memset.o memchr.o
>  obj-y += clear_page.o
> -obj-y += bitops.o find_next_bit.o
> +obj-y += bitops.o
>  obj-y += strchr.o strcmp.o strlen.o strncmp.o strnlen.o strrchr.o
> diff --git a/xen/arch/arm/include/asm/arm64/bitops.h
> b/xen/arch/arm/include/asm/arm64/bitops.h
> index d85a49bca4..0efde29068 100644
> --- a/xen/arch/arm/include/asm/arm64/bitops.h
> +++ b/xen/arch/arm/include/asm/arm64/bitops.h
> @@ -36,57 +36,13 @@ static inline int flsl(unsigned long x)
>  
>  /* Based on linux/include/asm-generic/bitops/find.h */
>  
> -#ifndef find_next_bit
> -/**
> - * find_next_bit - find the next set bit in a memory region
> - * @addr: The address to base the search on
> - * @offset: The bitnumber to start searching at
> - * @size: The bitmap size in bits
> - */
> -extern unsigned long find_next_bit(const unsigned long *addr,
> unsigned long
> -             size, unsigned long offset);
> -#endif
> -
> -#ifndef find_next_zero_bit
> -/**
> - * find_next_zero_bit - find the next cleared bit in a memory region
> - * @addr: The address to base the search on
> - * @offset: The bitnumber to start searching at
> - * @size: The bitmap size in bits
> - */
> -extern unsigned long find_next_zero_bit(const unsigned long *addr,
> unsigned
> -             long size, unsigned long offset);
> -#endif
> -
> -#ifdef CONFIG_GENERIC_FIND_FIRST_BIT
> -
> -/**
> - * find_first_bit - find the first set bit in a memory region
> - * @addr: The address to start the search at
> - * @size: The maximum size to search
> - *
> - * Returns the bit number of the first set bit.
> - */
> -extern unsigned long find_first_bit(const unsigned long *addr,
> -                                 unsigned long size);
> -
> -/**
> - * find_first_zero_bit - find the first cleared bit in a memory
> region
> - * @addr: The address to start the search at
> - * @size: The maximum size to search
> - *
> - * Returns the bit number of the first cleared bit.
> - */
> -extern unsigned long find_first_zero_bit(const unsigned long *addr,
> -                                      unsigned long size);
> -#else /* CONFIG_GENERIC_FIND_FIRST_BIT */
> +#ifndef CONFIG_GENERIC_FIND_FIRST_BIT
>  
>  #define find_first_bit(addr, size) find_next_bit((addr), (size), 0)
>  #define find_first_zero_bit(addr, size) find_next_zero_bit((addr),
> (size), 0)
>  
>  #endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
>  
> -
>  #endif /* _ARM_ARM64_BITOPS_H */
>  /*
>   * Local variables:
> diff --git a/xen/arch/ppc/include/asm/bitops.h
> b/xen/arch/ppc/include/asm/bitops.h
> index 5e7f36c21d..5820b9ce7b 100644
> --- a/xen/arch/ppc/include/asm/bitops.h
> +++ b/xen/arch/ppc/include/asm/bitops.h
> @@ -217,119 +217,4 @@ static always_inline unsigned long
> __ffs(unsigned long word)
>   */
>  #define find_first_set_bit(x) (ffsl(x) - 1)
>  
> -/*
> - * Find the first set bit in a memory region.
> - */
> -static inline unsigned long find_first_bit(const unsigned long
> *addr,
> -                                           unsigned long size)
> -{
> -    const unsigned long *p = addr;
> -    unsigned long result = 0;
> -    unsigned long tmp;
> -
> -    while ( size & ~(BITS_PER_LONG - 1) )
> -    {
> -        if ( (tmp = *(p++)) )
> -            goto found;
> -        result += BITS_PER_LONG;
> -        size -= BITS_PER_LONG;
> -    }
> -    if ( !size )
> -        return result;
> -
> -    tmp = (*p) & (~0UL >> (BITS_PER_LONG - size));
> -    if ( tmp == 0UL )         /* Are any bits set? */
> -        return result + size; /* Nope. */
> - found:
> -    return result + __ffs(tmp);
> -}
> -
> -static inline unsigned long find_next_bit(const unsigned long *addr,
> -                                          unsigned long size,
> -                                          unsigned long offset)
> -{
> -    const unsigned long *p = addr + BITOP_WORD(offset);
> -    unsigned long result = offset & ~(BITS_PER_LONG - 1);
> -    unsigned long tmp;
> -
> -    if ( offset >= size )
> -        return size;
> -    size -= result;
> -    offset %= BITS_PER_LONG;
> -    if ( offset )
> -    {
> -        tmp = *(p++);
> -        tmp &= (~0UL << offset);
> -        if ( size < BITS_PER_LONG )
> -            goto found_first;
> -        if ( tmp )
> -            goto found_middle;
> -        size -= BITS_PER_LONG;
> -        result += BITS_PER_LONG;
> -    }
> -    while ( size & ~(BITS_PER_LONG - 1) )
> -    {
> -        if ( (tmp = *(p++)) )
> -            goto found_middle;
> -        result += BITS_PER_LONG;
> -        size -= BITS_PER_LONG;
> -    }
> -    if ( !size )
> -        return result;
> -    tmp = *p;
> -
> - found_first:
> -    tmp &= (~0UL >> (BITS_PER_LONG - size));
> -    if ( tmp == 0UL )         /* Are any bits set? */
> -        return result + size; /* Nope. */
> - found_middle:
> -    return result + __ffs(tmp);
> -}
> -
> -/*
> - * This implementation of find_{first,next}_zero_bit was stolen from
> - * Linus' asm-alpha/bitops.h.
> - */
> -static inline unsigned long find_next_zero_bit(const unsigned long
> *addr,
> -                                               unsigned long size,
> -                                               unsigned long offset)
> -{
> -    const unsigned long *p = addr + BITOP_WORD(offset);
> -    unsigned long result = offset & ~(BITS_PER_LONG - 1);
> -    unsigned long tmp;
> -
> -    if ( offset >= size )
> -        return size;
> -    size -= result;
> -    offset %= BITS_PER_LONG;
> -    if ( offset )
> -    {
> -        tmp = *(p++);
> -        tmp |= ~0UL >> (BITS_PER_LONG - offset);
> -        if ( size < BITS_PER_LONG )
> -            goto found_first;
> -        if ( ~tmp )
> -            goto found_middle;
> -        size -= BITS_PER_LONG;
> -        result += BITS_PER_LONG;
> -    }
> -    while ( size & ~(BITS_PER_LONG - 1) )
> -    {
> -        if ( ~(tmp = *(p++)) )
> -            goto found_middle;
> -        result += BITS_PER_LONG;
> -        size -= BITS_PER_LONG;
> -    }
> -    if ( !size )
> -        return result;
> -    tmp = *p;
> -
> - found_first:
> -    tmp |= ~0UL << size;
> -    if ( tmp == ~0UL )        /* Are any bits zero? */
> -        return result + size; /* Nope. */
> - found_middle:
> -    return result + ffz(tmp);
> -}
> -
>  #endif /* _ASM_PPC_BITOPS_H */
> diff --git a/xen/include/xen/bitops.h b/xen/include/xen/bitops.h
> index 2cb7892bcc..e3c5a4ccf3 100644
> --- a/xen/include/xen/bitops.h
> +++ b/xen/include/xen/bitops.h
> @@ -105,6 +105,54 @@ static inline int generic_flsl(unsigned long x)
>   */
>  #include <asm/bitops.h>
>  
> +#ifndef find_next_bit
> +/**
> + * find_next_bit - find the next set bit in a memory region
> + * @addr: The address to base the search on
> + * @offset: The bitnumber to start searching at
> + * @size: The bitmap size in bits
> + */
> +extern unsigned long find_next_bit(const unsigned long *addr,
> +                                   unsigned long size,
> +                                   unsigned long offset);
> +#endif
> +
> +#ifndef find_next_zero_bit
> +/**
> + * find_next_zero_bit - find the next cleared bit in a memory region
> + * @addr: The address to base the search on
> + * @offset: The bitnumber to start searching at
> + * @size: The bitmap size in bits
> + */
> +extern unsigned long find_next_zero_bit(const unsigned long *addr,
> +                                        unsigned long size,
> +                                        unsigned long offset);
> +#endif
> +
> +#ifndef find_first_bit
> +/**
> + * find_first_bit - find the first set bit in a memory region
> + * @addr: The address to start the search at
> + * @size: The maximum size to search
> + *
> + * Returns the bit number of the first set bit.
> + */
> +extern unsigned long find_first_bit(const unsigned long *addr,
> +                                    unsigned long size);
> +#endif
> +
> +#ifndef find_first_zero_bit
> +/**
> + * find_first_zero_bit - find the first cleared bit in a memory
> region
> + * @addr: The address to start the search at
> + * @size: The maximum size to search
> + *
> + * Returns the bit number of the first cleared bit.
> + */
> +extern unsigned long find_first_zero_bit(const unsigned long *addr,
> +                                         unsigned long size);
> +#endif
> +
>  #if BITS_PER_LONG == 64
>  # define fls64 flsl
>  # define ffs64 ffsl
> diff --git a/xen/lib/Makefile b/xen/lib/Makefile
> index 2d9ebb945f..e63798e1d4 100644
> --- a/xen/lib/Makefile
> +++ b/xen/lib/Makefile
> @@ -3,6 +3,7 @@ obj-$(CONFIG_X86) += x86/
>  lib-y += bsearch.o
>  lib-y += ctors.o
>  lib-y += ctype.o
> +lib-y += find-next-bit.o
>  lib-y += list-sort.o
>  lib-y += memchr.o
>  lib-y += memchr_inv.o
> diff --git a/xen/arch/arm/arm64/lib/find_next_bit.c b/xen/lib/find-
> next-bit.c
> similarity index 100%
> rename from xen/arch/arm/arm64/lib/find_next_bit.c
> rename to xen/lib/find-next-bit.c