Commit 64970b68 authored by Alexander van Heukelum's avatar Alexander van Heukelum Committed by Ingo Molnar
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x86, generic: optimize find_next_(zero_)bit for small constant-size bitmaps



This moves an optimization for searching constant-sized small
bitmaps form x86_64-specific to generic code.

On an i386 defconfig (the x86#testing one), the size of vmlinux hardly
changes with this applied. I have observed only four places where this
optimization avoids a call into find_next_bit:

In the functions return_unused_surplus_pages, alloc_fresh_huge_page,
and adjust_pool_surplus, this patch avoids a call for a 1-bit bitmap.
In __next_cpu a call is avoided for a 32-bit bitmap. That's it.

On x86_64, 52 locations are optimized with a minimal increase in
code size:

Current #testing defconfig:
	146 x bsf, 27 x find_next_*bit
   text    data     bss     dec     hex filename
   5392637  846592  724424 6963653  6a41c5 vmlinux

After removing the x86_64 specific optimization for find_next_*bit:
	94 x bsf, 79 x find_next_*bit
   text    data     bss     dec     hex filename
   5392358  846592  724424 6963374  6a40ae vmlinux

After this patch (making the optimization generic):
	146 x bsf, 27 x find_next_*bit
   text    data     bss     dec     hex filename
   5392396  846592  724424 6963412  6a40d4 vmlinux

[ tglx@linutronix.de: build fixes ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 60b6783a
#ifndef _ASM_GENERIC_BITOPS_FIND_H_ #ifndef _ASM_GENERIC_BITOPS_FIND_H_
#define _ASM_GENERIC_BITOPS_FIND_H_ #define _ASM_GENERIC_BITOPS_FIND_H_
#ifndef CONFIG_GENERIC_FIND_NEXT_BIT
extern unsigned long find_next_bit(const unsigned long *addr, unsigned long extern unsigned long find_next_bit(const unsigned long *addr, unsigned long
size, unsigned long offset); size, unsigned long offset);
extern unsigned long find_next_zero_bit(const unsigned long *addr, unsigned extern unsigned long find_next_zero_bit(const unsigned long *addr, unsigned
long size, unsigned long offset); long size, unsigned long offset);
#endif
#define find_first_bit(addr, size) find_next_bit((addr), (size), 0) #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) #define find_first_zero_bit(addr, size) find_next_zero_bit((addr), (size), 0)
......
...@@ -306,12 +306,6 @@ static int test_bit(int nr, const volatile unsigned long *addr); ...@@ -306,12 +306,6 @@ static int test_bit(int nr, const volatile unsigned long *addr);
#undef BIT_ADDR #undef BIT_ADDR
#undef ADDR #undef ADDR
unsigned long find_next_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);
#ifdef CONFIG_X86_32 #ifdef CONFIG_X86_32
# include "bitops_32.h" # include "bitops_32.h"
#else #else
......
...@@ -15,16 +15,6 @@ static inline long __scanbit(unsigned long val, unsigned long max) ...@@ -15,16 +15,6 @@ static inline long __scanbit(unsigned long val, unsigned long max)
return val; return val;
} }
#define find_next_bit(addr,size,off) \
((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \
((off) + (__scanbit((*(unsigned long *)addr) >> (off),(size)-(off)))) : \
find_next_bit(addr,size,off)))
#define find_next_zero_bit(addr,size,off) \
((__builtin_constant_p(size) && (size) <= BITS_PER_LONG ? \
((off)+(__scanbit(~(((*(unsigned long *)addr)) >> (off)),(size)-(off)))) : \
find_next_zero_bit(addr,size,off)))
#define find_first_bit(addr, size) \ #define find_first_bit(addr, size) \
((__builtin_constant_p((size)) && (size) <= BITS_PER_LONG \ ((__builtin_constant_p((size)) && (size) <= BITS_PER_LONG \
? (__scanbit(*(unsigned long *)(addr), (size))) \ ? (__scanbit(*(unsigned long *)(addr), (size))) \
......
...@@ -112,4 +112,81 @@ static inline unsigned fls_long(unsigned long l) ...@@ -112,4 +112,81 @@ static inline unsigned fls_long(unsigned long l)
return fls64(l); return fls64(l);
} }
#ifdef __KERNEL__
#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);
/**
* 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);
}
#endif /* CONFIG_GENERIC_FIND_NEXT_BIT */
#endif /* __KERNEL__ */
#endif #endif
...@@ -15,17 +15,12 @@ ...@@ -15,17 +15,12 @@
#include <asm/byteorder.h> #include <asm/byteorder.h>
#define BITOP_WORD(nr) ((nr) / BITS_PER_LONG) #define BITOP_WORD(nr) ((nr) / BITS_PER_LONG)
#undef find_next_bit
#undef find_next_zero_bit /*
* Find the next set bit in a memory region.
/**
* 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 maximum size to search
*/ */
unsigned long find_next_bit(const unsigned long *addr, unsigned long size, unsigned long __find_next_bit(const unsigned long *addr,
unsigned long offset) unsigned long size, unsigned long offset)
{ {
const unsigned long *p = addr + BITOP_WORD(offset); const unsigned long *p = addr + BITOP_WORD(offset);
unsigned long result = offset & ~(BITS_PER_LONG-1); unsigned long result = offset & ~(BITS_PER_LONG-1);
...@@ -62,15 +57,14 @@ unsigned long find_next_bit(const unsigned long *addr, unsigned long size, ...@@ -62,15 +57,14 @@ unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
found_middle: found_middle:
return result + __ffs(tmp); 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 * This implementation of find_{first,next}_zero_bit was stolen from
* Linus' asm-alpha/bitops.h. * Linus' asm-alpha/bitops.h.
*/ */
unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size, unsigned long __find_next_zero_bit(const unsigned long *addr,
unsigned long offset) unsigned long size, unsigned long offset)
{ {
const unsigned long *p = addr + BITOP_WORD(offset); const unsigned long *p = addr + BITOP_WORD(offset);
unsigned long result = offset & ~(BITS_PER_LONG-1); unsigned long result = offset & ~(BITS_PER_LONG-1);
...@@ -107,8 +101,7 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size, ...@@ -107,8 +101,7 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
found_middle: found_middle:
return result + ffz(tmp); return result + ffz(tmp);
} }
EXPORT_SYMBOL(__find_next_zero_bit);
EXPORT_SYMBOL(find_next_zero_bit);
#ifdef __BIG_ENDIAN #ifdef __BIG_ENDIAN
......
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