[PATCH 12/14] lib: add fast path for find_first_*_bit() and find_last_bit()

Yury Norov
2021-02-18T04:12:51Z

Similarly to bitmap functions, users would benefit if we'll handle
a case of small-size bitmaps that fit into a single word.

While here, move the find_last_bit() declaration to bitops/find.h
where other find_*_bit() functions sit.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
include/asm-generic/bitops/find.h | 50 ++++++++++++++++++++++++++++---
include/linux/bitops.h | 12 --------
lib/find_bit.c | 12 ++++----
3 files changed, 52 insertions(+), 22 deletions(-)

diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
index 8bd7a33a889d..3633a37cec38 100644
--- a/include/asm-generic/bitops/find.h
+++ b/include/asm-generic/bitops/find.h
@@ -5,6 +5,9 @@
extern unsigned long _find_next_bit(const unsigned long *addr1,
const unsigned long *addr2, unsigned long nbits,
unsigned long start, unsigned long invert, unsigned long le);
+extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
+extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
+extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long size);

#ifndef find_next_bit
/**
@@ -102,8 +105,17 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
* Returns the bit number of the first set bit.
* If no bits are set, returns @size.
*/
-extern unsigned long find_first_bit(const unsigned long *addr,
- unsigned long size);
+static inline
+unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
+{
+ if (SMALL_CONST(size - 1)) {
+ unsigned long val = *addr & BITS_FIRST(size - 1);
+
+ return val ? __ffs(val) : size;
+ }
+
+ return _find_first_bit(addr, size);
+}

/**
* find_first_zero_bit - find the first cleared bit in a memory region
@@ -113,8 +125,17 @@ extern unsigned long find_first_bit(const unsigned long *addr,
* Returns the bit number of the first cleared bit.
* If no bits are zero, returns @size.
*/
-extern unsigned long find_first_zero_bit(const unsigned long *addr,
- unsigned long size);
+static inline
+unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
+{
+ if (SMALL_CONST(size - 1)) {
+ unsigned long val = *addr | ~BITS_FIRST(size - 1);
+
+ return val == ~0UL ? size : ffz(val);
+ }
+
+ return _find_first_zero_bit(addr, size);
+}
#else /* CONFIG_GENERIC_FIND_FIRST_BIT */

#ifndef find_first_bit
@@ -126,6 +147,27 @@ extern unsigned long find_first_zero_bit(const unsigned long *addr,

#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */

+#ifndef find_last_bit
+/**
+ * find_last_bit - find the last set bit in a memory region
+ * @addr: The address to start the search at
+ * @size: The number of bits to search
+ *
+ * Returns the bit number of the last set bit, or size.
+ */
+static inline
+unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
+{
+ if (SMALL_CONST(size - 1)) {
+ unsigned long val = *addr & BITS_FIRST(size - 1);
+
+ return val ? __fls(val) : size;
+ }
+
+ return _find_last_bit(addr, size);
+}
+#endif
+
/**
* find_next_clump8 - find next 8-bit clump with set bits in a memory region
* @clump: location to store copy of found clump
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index a5a48303b0f1..26bf15e6cd35 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -286,17 +286,5 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
})
#endif

-#ifndef find_last_bit
-/**
- * find_last_bit - find the last set bit in a memory region
- * @addr: The address to start the search at
- * @size: The number of bits to search
- *
- * Returns the bit number of the last set bit, or size.
- */
-extern unsigned long find_last_bit(const unsigned long *addr,
- unsigned long size);
-#endif
-
#endif /* __KERNEL__ */
#endif
diff --git a/lib/find_bit.c b/lib/find_bit.c
index 2470ae390f3c..e2c301d28568 100644
--- a/lib/find_bit.c
+++ b/lib/find_bit.c
@@ -75,7 +75,7 @@ EXPORT_SYMBOL(_find_next_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)
{
unsigned long idx;

@@ -86,14 +86,14 @@ unsigned long find_first_bit(const unsigned long *addr, unsigned long size)

return size;
}
-EXPORT_SYMBOL(find_first_bit);
+EXPORT_SYMBOL(_find_first_bit);
#endif

#ifndef find_first_zero_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)
{
unsigned long idx;

@@ -104,11 +104,11 @@ unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)

return size;
}
-EXPORT_SYMBOL(find_first_zero_bit);
+EXPORT_SYMBOL(_find_first_zero_bit);
#endif

#ifndef find_last_bit
-unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
+unsigned long _find_last_bit(const unsigned long *addr, unsigned long size)
{
if (size) {
unsigned long val = BITS_FIRST_MASK(size - 1);
@@ -124,7 +124,7 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
}
return size;
}
-EXPORT_SYMBOL(find_last_bit);
+EXPORT_SYMBOL(_find_last_bit);
#endif

unsigned long find_next_clump8(unsigned long *clump, const unsigned long *addr,
--
2.25.1