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Subject[PATCH] x86: Change x86 to use generic find_next_bit
x86: Change x86 to use the generic find_next_bit implementation

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)

arch/x86/Kconfig | 3 ++
arch/x86/lib/Makefile | 2 +-
arch/x86/lib/bitops_32.c | 70 -------------------------------------------
arch/x86/lib/bitops_64.c | 68 -----------------------------------------
include/asm-x86/bitops.h | 6 ++++
include/asm-x86/bitops_32.h | 16 ----------
include/asm-x86/bitops_64.h | 2 -
lib/find_next_bit.c | 2 +
8 files changed, 12 insertions(+), 157 deletions(-)
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>

---
Hi,

I think it would be a good idea to use the generic versions of
find_next_bit and find_next_zero_bit. The i386 versions have
a bug, and the generic ones are faster (in my probably
not-so-representative micro-benchmark, that is).

Patch is against -x86#testing. It compiles.

Greetings,
Alexander

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ab85a04..29a5a38 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -83,6 +83,9 @@ config GENERIC_BUG
def_bool y
depends on BUG

+config GENERIC_FIND_NEXT_BIT
+ def_bool y
+
config GENERIC_HWEIGHT
def_bool y

diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 25df1c1..4360932 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -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
diff --git a/arch/x86/lib/bitops_32.c b/arch/x86/lib/bitops_32.c
deleted file mode 100644
index b654404..0000000
--- a/arch/x86/lib/bitops_32.c
+++ /dev/null
@@ -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);
diff --git a/arch/x86/lib/bitops_64.c b/arch/x86/lib/bitops_64.c
index 0e8f491..0eeb704 100644
--- a/arch/x86/lib/bitops_64.c
+++ b/arch/x86/lib/bitops_64.c
@@ -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);
diff --git a/include/asm-x86/bitops.h b/include/asm-x86/bitops.h
index 1a23ce1..7fbf93a 100644
--- a/include/asm-x86/bitops.h
+++ b/include/asm-x86/bitops.h
@@ -312,6 +312,12 @@ static int test_bit(int nr, const volatile unsigned long *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
diff --git a/include/asm-x86/bitops_32.h b/include/asm-x86/bitops_32.h
index e4d75fc..570f0fa 100644
--- a/include/asm-x86/bitops_32.h
+++ b/include/asm-x86/bitops_32.h
@@ -38,14 +38,6 @@ static inline int find_first_zero_bit(const unsigned long *addr, unsigned size)
}

/**
- * 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
*
@@ -81,14 +73,6 @@ static inline unsigned find_first_bit(const unsigned long *addr, unsigned size)
}

/**
- * 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
*
diff --git a/include/asm-x86/bitops_64.h b/include/asm-x86/bitops_64.h
index aaf1519..40bf0f8 100644
--- a/include/asm-x86/bitops_64.h
+++ b/include/asm-x86/bitops_64.h
@@ -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)
diff --git a/lib/find_next_bit.c b/lib/find_next_bit.c
index 78ccd73..5820e07 100644
--- a/lib/find_next_bit.c
+++ b/lib/find_next_bit.c
@@ -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


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