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bitops: remove "optimizations"
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The mapsize optimizations which were moved from x86 to the generic
code in commit 64970b6 increased the
binary size on non x86 architectures.

Looking into the real effects of the "optimizations" it turned out
that they are not used in find_next_bit() and find_next_zero_bit().

The ones in find_first_bit() and find_first_zero_bit() are used in a
couple of places but none of them is a real hot path.

Remove the "optimizations" all together and call the library functions
unconditionally.

Boot-tested on x86 and compile tested on every cross compiler I have.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@KAGA-KOKO @torvalds
KAGA-KOKO authored and torvalds committed Apr 29, 2008
1 parent 8972331 commit fee4b19
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Showing 2 changed files with 22 additions and 115 deletions.
115 changes: 12 additions & 103 deletions include/linux/bitops.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -114,8 +114,6 @@ static inline unsigned fls_long(unsigned long l)

#ifdef __KERNEL__
#ifdef CONFIG_GENERIC_FIND_FIRST_BIT
extern unsigned long __find_first_bit(const unsigned long *addr,
unsigned long size);

/**
* find_first_bit - find the first set bit in a memory region
Expand All @@ -124,28 +122,8 @@ extern unsigned long __find_first_bit(const unsigned long *addr,
*
* Returns the bit number of the first set bit.
*/
static __always_inline unsigned long
find_first_bit(const unsigned long *addr, unsigned long size)
{
/* Avoid a function call if the bitmap size is a constant */
/* and not bigger than BITS_PER_LONG. */

/* insert a sentinel so that __ffs returns size if there */
/* are no set bits in the bitmap */
if (__builtin_constant_p(size) && (size < BITS_PER_LONG))
return __ffs((*addr) | (1ul << size));

/* the result of __ffs(0) is undefined, so it needs to be */
/* handled separately */
if (__builtin_constant_p(size) && (size == BITS_PER_LONG))
return ((*addr) == 0) ? BITS_PER_LONG : __ffs(*addr);

/* size is not constant or too big */
return __find_first_bit(addr, size);
}

extern unsigned long __find_first_zero_bit(const unsigned long *addr,
unsigned long size);
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
Expand All @@ -154,102 +132,33 @@ extern unsigned long __find_first_zero_bit(const unsigned long *addr,
*
* Returns the bit number of the first cleared bit.
*/
static __always_inline unsigned long
find_first_zero_bit(const unsigned long *addr, unsigned long size)
{
/* Avoid a function call if the bitmap size is a constant */
/* and not bigger than BITS_PER_LONG. */

/* insert a sentinel so that __ffs returns size if there */
/* are no set bits in the bitmap */
if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
return __ffs(~(*addr) | (1ul << size));
}

/* the result of __ffs(0) is undefined, so it needs to be */
/* handled separately */
if (__builtin_constant_p(size) && (size == BITS_PER_LONG))
return (~(*addr) == 0) ? BITS_PER_LONG : __ffs(~(*addr));

/* size is not constant or too big */
return __find_first_zero_bit(addr, size);
}
extern unsigned long find_first_zero_bit(const unsigned long *addr,
unsigned long size);

#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */

#ifdef CONFIG_GENERIC_FIND_NEXT_BIT
extern unsigned long __find_next_bit(const unsigned long *addr,
unsigned long size, unsigned long offset);

/**
* 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
*/
static __always_inline unsigned long
find_next_bit(const unsigned long *addr, unsigned long size,
unsigned long offset)
{
unsigned long value;

/* Avoid a function call if the bitmap size is a constant */
/* and not bigger than BITS_PER_LONG. */

/* insert a sentinel so that __ffs returns size if there */
/* are no set bits in the bitmap */
if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
value = (*addr) & ((~0ul) << offset);
value |= (1ul << size);
return __ffs(value);
}

/* the result of __ffs(0) is undefined, so it needs to be */
/* handled separately */
if (__builtin_constant_p(size) && (size == BITS_PER_LONG)) {
value = (*addr) & ((~0ul) << offset);
return (value == 0) ? BITS_PER_LONG : __ffs(value);
}

/* size is not constant or too big */
return __find_next_bit(addr, size, offset);
}

extern unsigned long __find_next_zero_bit(const unsigned long *addr,
unsigned long size, unsigned long offset);
extern unsigned long find_next_bit(const unsigned long *addr,
unsigned long size, unsigned long offset);

/**
* 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
*/
static __always_inline unsigned long
find_next_zero_bit(const unsigned long *addr, unsigned long size,
unsigned long offset)
{
unsigned long value;

/* Avoid a function call if the bitmap size is a constant */
/* and not bigger than BITS_PER_LONG. */

/* insert a sentinel so that __ffs returns size if there */
/* are no set bits in the bitmap */
if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
value = (~(*addr)) & ((~0ul) << offset);
value |= (1ul << size);
return __ffs(value);
}

/* the result of __ffs(0) is undefined, so it needs to be */
/* handled separately */
if (__builtin_constant_p(size) && (size == BITS_PER_LONG)) {
value = (~(*addr)) & ((~0ul) << offset);
return (value == 0) ? BITS_PER_LONG : __ffs(value);
}

/* size is not constant or too big */
return __find_next_zero_bit(addr, size, offset);
}

extern unsigned long find_next_zero_bit(const unsigned long *addr,
unsigned long size,
unsigned long offset);

#endif /* CONFIG_GENERIC_FIND_NEXT_BIT */
#endif /* __KERNEL__ */
#endif
22 changes: 10 additions & 12 deletions lib/find_next_bit.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,8 @@
/*
* Find the next set bit in a memory region.
*/
unsigned long __find_next_bit(const unsigned long *addr,
unsigned long size, unsigned long offset)
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);
Expand Down Expand Up @@ -58,14 +58,14 @@ unsigned long __find_next_bit(const unsigned long *addr,
found_middle:
return result + __ffs(tmp);
}
EXPORT_SYMBOL(__find_next_bit);
EXPORT_SYMBOL(find_next_bit);

/*
* This implementation of find_{first,next}_zero_bit was stolen from
* Linus' asm-alpha/bitops.h.
*/
unsigned long __find_next_zero_bit(const unsigned long *addr,
unsigned long size, unsigned long offset)
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);
Expand Down Expand Up @@ -102,15 +102,14 @@ unsigned long __find_next_zero_bit(const unsigned long *addr,
found_middle:
return result + ffz(tmp);
}
EXPORT_SYMBOL(__find_next_zero_bit);
EXPORT_SYMBOL(find_next_zero_bit);
#endif /* CONFIG_GENERIC_FIND_NEXT_BIT */

#ifdef CONFIG_GENERIC_FIND_FIRST_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)
{
const unsigned long *p = addr;
unsigned long result = 0;
Expand All @@ -131,13 +130,12 @@ unsigned long __find_first_bit(const unsigned long *addr,
found:
return result + __ffs(tmp);
}
EXPORT_SYMBOL(__find_first_bit);
EXPORT_SYMBOL(find_first_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)
{
const unsigned long *p = addr;
unsigned long result = 0;
Expand All @@ -158,7 +156,7 @@ unsigned long __find_first_zero_bit(const unsigned long *addr,
found:
return result + ffz(tmp);
}
EXPORT_SYMBOL(__find_first_zero_bit);
EXPORT_SYMBOL(find_first_zero_bit);
#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */

#ifdef __BIG_ENDIAN
Expand Down

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