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x86: change x86 to use generic find_next_bit 

The versions with inline assembly are in fact slower on the machines I
tested them on (in userspace) (Athlon XP 2800+, p4-like Xeon 2.8GHz, AMD
Opteron 270). The i386-version needed a fix similar to 06024f21 to avoid
crashing the benchmark.

Benchmark using: gcc -fomit-frame-pointer -Os. For each bitmap size
1...512, for each possible bitmap with one bit set, for each possible
offset: find the position of the first bit starting at offset. If you
follow ;). Times include setup of the bitmap and checking of the
results.

		Athlon		Xeon		Opteron 32/64bit
x86-specific:	0m3.692s	0m2.820s	0m3.196s / 0m2.480s
generic:	0m2.622s	0m1.662s	0m2.100s / 0m1.572s

If the bitmap size is not a multiple of BITS_PER_LONG, and no set
(cleared) bit is found, find_next_bit (find_next_zero_bit) returns a
value outside of the range [0, size]. The generic version always returns
exactly size. The generic version also uses unsigned long everywhere,
while the x86 versions use a mishmash of int, unsigned (int), long and
unsigned long.

Using the generic version does give a slightly bigger kernel, though.

defconfig:	   text    data     bss     dec     hex filename
x86-specific:	4738555  481232  626688 5846475  5935cb vmlinux (32 bit)
generic:	4738621  481232  626688 5846541  59360d vmlinux (32 bit)
x86-specific:	5392395  846568  724424 6963387  6a40bb vmlinux (64 bit)
generic:	5392458  846568  724424 6963450  6a40fa vmlinux (64 bit)

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Alexander van Heukelum 2008-03-09 21:01:04 +01:00 committed by Ingo Molnar
parent 18e413f719
commit 6fd92b63d0
8 changed files with 12 additions and 157 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/Kconfig
View File

@ -77,6 +77,9 @@ config GENERIC_BUG
def_bool y
depends on BUG
config GENERIC_FIND_NEXT_BIT
def_bool y
config GENERIC_HWEIGHT
def_bool y

2
arch/x86/lib/Makefile
View File

@ -11,7 +11,7 @@ lib-y += memcpy_$(BITS).o
ifeq ($(CONFIG_X86_32),y)
lib-y += checksum_32.o
lib-y += strstr_32.o
lib-y += bitops_32.o semaphore_32.o string_32.o
lib-y += semaphore_32.o string_32.o
lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
else

70
arch/x86/lib/bitops_32.c
View File

@ -1,70 +0,0 @@
#include <linux/bitops.h>
#include <linux/module.h>
/**
* 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
*/
int find_next_bit(const unsigned long *addr, int size, int offset)
{
const unsigned long *p = addr + (offset >> 5);
int set = 0, bit = offset & 31, res;
if (bit) {
/*
* Look for nonzero in the first 32 bits:
*/
__asm__("bsfl %1,%0\n\t"
"jne 1f\n\t"
"movl $32, %0\n"
"1:"
: "=r" (set)
: "r" (*p >> bit));
if (set < (32 - bit))
return set + offset;
set = 32 - bit;
p++;
}
/*
* No set bit yet, search remaining full words for a bit
*/
res = find_first_bit (p, size - 32 * (p - addr));
return (offset + set + res);
}
EXPORT_SYMBOL(find_next_bit);
/**
* find_next_zero_bit - find the first zero 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
*/
int find_next_zero_bit(const unsigned long *addr, int size, int offset)
{
const unsigned long *p = addr + (offset >> 5);
int set = 0, bit = offset & 31, res;
if (bit) {
/*
* Look for zero in the first 32 bits.
*/
__asm__("bsfl %1,%0\n\t"
"jne 1f\n\t"
"movl $32, %0\n"
"1:"
: "=r" (set)
: "r" (~(*p >> bit)));
if (set < (32 - bit))
return set + offset;
set = 32 - bit;
p++;
}
/*
* No zero yet, search remaining full bytes for a zero
*/
res = find_first_zero_bit(p, size - 32 * (p - addr));
return (offset + set + res);
}
EXPORT_SYMBOL(find_next_zero_bit);

68
arch/x86/lib/bitops_64.c
View File

@ -1,9 +1,7 @@
#include <linux/bitops.h>
#undef find_first_zero_bit
#undef find_next_zero_bit
#undef find_first_bit
#undef find_next_bit
static inline long
__find_first_zero_bit(const unsigned long * addr, unsigned long size)
@ -57,39 +55,6 @@ long find_first_zero_bit(const unsigned long * addr, unsigned long size)
return __find_first_zero_bit (addr, size);
}
/**
* find_next_zero_bit - find the next zero 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
*/
long find_next_zero_bit (const unsigned long * addr, long size, long offset)
{
const unsigned long * p = addr + (offset >> 6);
unsigned long set = 0;
unsigned long res, bit = offset&63;
if (bit) {
/*
* Look for zero in first word
*/
asm("bsfq %1,%0\n\t"
"cmoveq %2,%0"
: "=r" (set)
: "r" (~(*p >> bit)), "r"(64L));
if (set < (64 - bit))
return set + offset;
set = 64 - bit;
p++;
}
/*
* No zero yet, search remaining full words for a zero
*/
res = __find_first_zero_bit (p, size - 64 * (p - addr));
return (offset + set + res);
}
static inline long
__find_first_bit(const unsigned long * addr, unsigned long size)
{
@ -136,40 +101,7 @@ long find_first_bit(const unsigned long * addr, unsigned long size)
return __find_first_bit(addr,size);
}
/**
* find_next_bit - find the first 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
*/
long find_next_bit(const unsigned long * addr, long size, long offset)
{
const unsigned long * p = addr + (offset >> 6);
unsigned long set = 0, bit = offset & 63, res;
if (bit) {
/*
* Look for nonzero in the first 64 bits:
*/
asm("bsfq %1,%0\n\t"
"cmoveq %2,%0\n\t"
: "=r" (set)
: "r" (*p >> bit), "r" (64L));
if (set < (64 - bit))
return set + offset;
set = 64 - bit;
p++;
}
/*
* No set bit yet, search remaining full words for a bit
*/
res = __find_first_bit (p, size - 64 * (p - addr));
return (offset + set + res);
}
#include <linux/module.h>
EXPORT_SYMBOL(find_next_bit);
EXPORT_SYMBOL(find_first_bit);
EXPORT_SYMBOL(find_first_zero_bit);
EXPORT_SYMBOL(find_next_zero_bit);

6
include/asm-x86/bitops.h
View File

@ -306,6 +306,12 @@ static int test_bit(int nr, const volatile unsigned long *addr);
#undef BIT_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
# include "bitops_32.h"
#else

16
include/asm-x86/bitops_32.h
View File

@ -39,14 +39,6 @@ static inline int find_first_zero_bit(const unsigned long *addr, unsigned size)
return res;
}
/**
* find_next_zero_bit - find the first zero bit in a memory region
* @addr: The address to base the search on
* @offset: The bit number to start searching at
* @size: The maximum size to search
*/
int find_next_zero_bit(const unsigned long *addr, int size, int offset);
/**
* __ffs - find first bit in word.
* @word: The word to search
@ -82,14 +74,6 @@ static inline unsigned find_first_bit(const unsigned long *addr, unsigned size)
return x;
}
/**
* find_next_bit - find the first set bit in a memory region
* @addr: The address to base the search on
* @offset: The bit number to start searching at
* @size: The maximum size to search
*/
int find_next_bit(const unsigned long *addr, int size, int offset);
/**
* ffz - find first zero in word.
* @word: The word to search

2
include/asm-x86/bitops_64.h
View File

@ -6,9 +6,7 @@
*/
extern long find_first_zero_bit(const unsigned long *addr, unsigned long size);
extern long find_next_zero_bit(const unsigned long *addr, long size, long offset);
extern long find_first_bit(const unsigned long *addr, unsigned long size);
extern long find_next_bit(const unsigned long *addr, long size, long offset);
/* return index of first bet set in val or max when no bit is set */
static inline long __scanbit(unsigned long val, unsigned long max)

2
lib/find_next_bit.c
View File

@ -15,6 +15,8 @@
#include <asm/byteorder.h>
#define BITOP_WORD(nr) ((nr) / BITS_PER_LONG)
#undef find_next_bit
#undef find_next_zero_bit
/**
* find_next_bit - find the next set bit in a memory region