find_fisrt_{zero_}bit are too heavy for bitmap_{full,empty}. We don't
need to calculate and compare the position of bitmap. This set of patch
instroduces lightweight api and replaces the heavy one.
v2: Move the declarations to linux/bitops.h for compilation
Jia He (3):
Move 2 mask macro from bitmap.h to bitops.h
Introduce 2 bit ops api: all_is_bit_{one,zero}
Replace find_fisrt_{zero_}bit with the new lightweight api
include/linux/bitmap.h | 7 ++-----
include/linux/bitops.h | 7 +++++++
lib/find_bit.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 59 insertions(+), 5 deletions(-)
--
2.5.0
This patch moves the mask macro to bitops.h and then the new introduced
api in find_bit.c can use it.
Signed-off-by: Jia He <[email protected]>
---
include/linux/bitmap.h | 3 ---
include/linux/bitops.h | 4 ++++
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 9653fdb..15524f6 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -172,9 +172,6 @@ extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned int
extern int bitmap_print_to_pagebuf(bool list, char *buf,
const unsigned long *maskp, int nmaskbits);
-#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
-#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
-
#define small_const_nbits(nbits) \
(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 2b8ed12..b881028 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -24,6 +24,10 @@
#define GENMASK_ULL(h, l) \
(((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
+/* For bitmap ops*/
+#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
+#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
+
extern unsigned int __sw_hweight8(unsigned int w);
extern unsigned int __sw_hweight16(unsigned int w);
extern unsigned int __sw_hweight32(unsigned int w);
--
2.5.0
This patch introduces 2 lightweight bit api.
all_bit_is_zero return 1 if the bit string is all zero.
The addr is the start address, the size is the bit size of the bit string.
all_bit_is_one is the opposite.
Signed-off-by: Jia He <[email protected]>
---
lib/find_bit.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
diff --git a/lib/find_bit.c b/lib/find_bit.c
index 18072ea..1d56d8d 100644
--- a/lib/find_bit.c
+++ b/lib/find_bit.c
@@ -131,6 +131,56 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
EXPORT_SYMBOL(find_last_bit);
#endif
+#ifndef all_bit_is_zero
+/*
+ * return val: 1 means all bit is zero
+ */
+unsigned int all_bit_is_zero(const unsigned long *addr, unsigned size)
+{
+ unsigned long idx;
+ unsigned long mask = size;
+
+ if (unlikely(size == 0))
+ return 1;
+
+ if (size > BITS_PER_LONG) {
+ for (idx = 0; idx * BITS_PER_LONG < size; idx++)
+ if (addr[idx])
+ return 0;
+
+ mask = size - (idx - 1) * BITS_PER_LONG;
+ }
+
+ return !(*addr & BITMAP_LAST_WORD_MASK(mask));
+}
+EXPORT_SYMBOL(all_bit_is_zero);
+#endif
+
+#ifndef all_bit_is_one
+/*
+ * return val: 1 means all bit is one
+ */
+unsigned int all_bit_is_one(const unsigned long *addr, unsigned size)
+{
+ unsigned long idx;
+ unsigned long mask = size;
+
+ if (unlikely(size == 0))
+ return 1;
+
+ if (size > BITS_PER_LONG) {
+ for (idx = 0; idx * BITS_PER_LONG < size; idx++)
+ if (~addr[idx])
+ return 0;
+
+ mask = size - (idx - 1) * BITS_PER_LONG;
+ }
+
+ return !(~(*addr) & BITMAP_LAST_WORD_MASK(mask));
+}
+EXPORT_SYMBOL(all_bit_is_one);
+#endif
+
#ifdef __BIG_ENDIAN
/* include/linux/byteorder does not support "unsigned long" type */
--
2.5.0
This is to replace find_fisrt_{zero_}bit with the new lightweight api
all_bit_is_{one,zero} in bitmap_{full,empty}
Signed-off-by: Jia He <[email protected]>
---
include/linux/bitmap.h | 4 ++--
include/linux/bitops.h | 3 +++
2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 15524f6..8877a68 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -281,7 +281,7 @@ static inline int bitmap_empty(const unsigned long *src, unsigned nbits)
if (small_const_nbits(nbits))
return ! (*src & BITMAP_LAST_WORD_MASK(nbits));
- return find_first_bit(src, nbits) == nbits;
+ return all_bit_is_zero(src, nbits);
}
static inline int bitmap_full(const unsigned long *src, unsigned int nbits)
@@ -289,7 +289,7 @@ static inline int bitmap_full(const unsigned long *src, unsigned int nbits)
if (small_const_nbits(nbits))
return ! (~(*src) & BITMAP_LAST_WORD_MASK(nbits));
- return find_first_zero_bit(src, nbits) == nbits;
+ return all_bit_is_one(src, nbits);
}
static __always_inline int bitmap_weight(const unsigned long *src, unsigned int nbits)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index b881028..e34f2ff 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -214,6 +214,9 @@ static inline unsigned long __ffs64(u64 word)
return __ffs((unsigned long)word);
}
+extern unsigned int all_bit_is_one(const unsigned long *addr, unsigned size);
+extern unsigned int all_bit_is_zero(const unsigned long *addr, unsigned size);
+
#ifdef __KERNEL__
#ifndef set_mask_bits
--
2.5.0
hi, jia
Nice patch. But I have one minor question. see inline comments.
On 2015/11/19 14:48, Jia He wrote:
> This patch introduces 2 lightweight bit api.
> all_bit_is_zero return 1 if the bit string is all zero.
> The addr is the start address, the size is the bit size of the bit string.
> all_bit_is_one is the opposite.
>
> Signed-off-by: Jia He <[email protected]>
> ---
> lib/find_bit.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 50 insertions(+)
>
> diff --git a/lib/find_bit.c b/lib/find_bit.c
> index 18072ea..1d56d8d 100644
> --- a/lib/find_bit.c
> +++ b/lib/find_bit.c
> @@ -131,6 +131,56 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
> EXPORT_SYMBOL(find_last_bit);
> #endif
>
> +#ifndef all_bit_is_zero
> +/*
> + * return val: 1 means all bit is zero
> + */
> +unsigned int all_bit_is_zero(const unsigned long *addr, unsigned size)
> +{
Seems better that size should be type of "unsigned long". Otherwise I'm afraid when we compare idx * BITS_PER_LONG with size, there might be overflow issue.
> + unsigned long idx;
> + unsigned long mask = size;
> +
> + if (unlikely(size == 0))
> + return 1;
> +
> + if (size > BITS_PER_LONG) {
> + for (idx = 0; idx * BITS_PER_LONG < size; idx++)
> + if (addr[idx])
> + return 0;
> +
> + mask = size - (idx - 1) * BITS_PER_LONG;
> + }
> +
> + return !(*addr & BITMAP_LAST_WORD_MASK(mask));
> +}
> +EXPORT_SYMBOL(all_bit_is_zero);
> +#endif
> +
> +#ifndef all_bit_is_one
> +/*
> + * return val: 1 means all bit is one
> + */
> +unsigned int all_bit_is_one(const unsigned long *addr, unsigned size)
> +{
this argc of size should be type of "unsigned long", too.
thanks
xinhui
> + unsigned long idx;
> + unsigned long mask = size;
> +
> + if (unlikely(size == 0))
> + return 1;
> +
> + if (size > BITS_PER_LONG) {
> + for (idx = 0; idx * BITS_PER_LONG < size; idx++)
> + if (~addr[idx])
> + return 0;
> +
> + mask = size - (idx - 1) * BITS_PER_LONG;
> + }
> +
> + return !(~(*addr) & BITMAP_LAST_WORD_MASK(mask));
> +}
> +EXPORT_SYMBOL(all_bit_is_one);
> +#endif
> +
> #ifdef __BIG_ENDIAN
>
> /* include/linux/byteorder does not support "unsigned long" type */
>
> On Nov 19, 2015, at 14:48, Jia He <[email protected]> wrote:
>
>
why not use memcmp() to compare with 0x0000000 or 0xffffffff ?
memcmp() have better performance on some platforms .
Thanks
Thanks， I will add it in next verison
B.R.
Justin
在 11/19/15 4:40 PM, xinhui 写道:
> hi, jia
> Nice patch. But I have one minor question. see inline comments.
>
> On 2015/11/19 14:48, Jia He wrote:
>> This patch introduces 2 lightweight bit api.
>> all_bit_is_zero return 1 if the bit string is all zero.
>> The addr is the start address, the size is the bit size of the bit
>> string.
>> all_bit_is_one is the opposite.
>>
>> Signed-off-by: Jia He <[email protected]>
>> ---
>> lib/find_bit.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 50 insertions(+)
>>
>> diff --git a/lib/find_bit.c b/lib/find_bit.c
>> index 18072ea..1d56d8d 100644
>> --- a/lib/find_bit.c
>> +++ b/lib/find_bit.c
>> @@ -131,6 +131,56 @@ unsigned long find_last_bit(const unsigned long
>> *addr, unsigned long size)
>> EXPORT_SYMBOL(find_last_bit);
>> #endif
>>
>> +#ifndef all_bit_is_zero
>> +/*
>> + * return val: 1 means all bit is zero
>> + */
>> +unsigned int all_bit_is_zero(const unsigned long *addr, unsigned size)
>> +{
> Seems better that size should be type of "unsigned long". Otherwise
> I'm afraid when we compare idx * BITS_PER_LONG with size, there might
> be overflow issue.
>
>> + unsigned long idx;
>> + unsigned long mask = size;
>> +
>> + if (unlikely(size == 0))
>> + return 1;
>> +
>> + if (size > BITS_PER_LONG) {
>> + for (idx = 0; idx * BITS_PER_LONG < size; idx++)
>> + if (addr[idx])
>> + return 0;
>> +
>> + mask = size - (idx - 1) * BITS_PER_LONG;
>> + }
>> +
>> + return !(*addr & BITMAP_LAST_WORD_MASK(mask));
>> +}
>> +EXPORT_SYMBOL(all_bit_is_zero);
>> +#endif
>> +
>> +#ifndef all_bit_is_one
>> +/*
>> + * return val: 1 means all bit is one
>> + */
>> +unsigned int all_bit_is_one(const unsigned long *addr, unsigned size)
>> +{
> this argc of size should be type of "unsigned long", too.
>
> thanks
> xinhui
>
>> + unsigned long idx;
>> + unsigned long mask = size;
>> +
>> + if (unlikely(size == 0))
>> + return 1;
>> +
>> + if (size > BITS_PER_LONG) {
>> + for (idx = 0; idx * BITS_PER_LONG < size; idx++)
>> + if (~addr[idx])
>> + return 0;
>> +
>> + mask = size - (idx - 1) * BITS_PER_LONG;
>> + }
>> +
>> + return !(~(*addr) & BITMAP_LAST_WORD_MASK(mask));
>> +}
>> +EXPORT_SYMBOL(all_bit_is_one);
>> +#endif
>> +
>> #ifdef __BIG_ENDIAN
>>
>> /* include/linux/byteorder does not support "unsigned long" type */
>>
>
> --
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>
On Thu, Nov 19 2015, Jia He <[email protected]> wrote:
> find_fisrt_{zero_}bit are too heavy for bitmap_{full,empty}. We don't
> need to calculate and compare the position of bitmap. This set of patch
> instroduces lightweight api and replaces the heavy one.
>
Please check the history of the code you're modifying. git blame
include/linux/bitmap.h would immediately point you to 2afe27c718b
"lib/bitmap.c: bitmap_[empty,full]: remove code duplication". While it's
obviously true that find_first_bit does slightly more work than strictly
necessary to establish whether the bitmap is empty, it does the same
number of memory accesses, so I wouldn't consider it particularly
heavy-weight. Getting rid of .text as 2afe27c718b did is a good thing,
so you'd have to explain why we should reintroduce specialized functions
for this.
Your code is also buggy :-(
Rasmus