[8/8] lib: add fast path for find_first_*_bit() and find_last_bit()

Commit Message

Yury Norov Jan. 30, 2021, 7:17 p.m. UTC

Similarly to bitmap functions, users will 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 <[e-mail]>
---
 include/asm-generic/bitops/find.h       | 50 +++++++++++++++++++++++--
 include/linux/bitops.h                  | 12 ------
 lib/find_bit.c                          | 12 +++---
 tools/include/asm-generic/bitops/find.h | 28 ++++++++++++--
 tools/lib/find_bit.c                    |  4 +-
 5 files changed, 79 insertions(+), 27 deletions(-)

Comments

Andy Shevchenko Feb. 1, 2021, 1:50 p.m. UTC | #1

On Sat, Jan 30, 2021 at 11:17:19AM -0800, Yury Norov wrote:
> Similarly to bitmap functions, users will 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.

As per previous patches:
 - decouple from tools
 - show examples of the code generation difference

Patch

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,
diff --git a/tools/include/asm-generic/bitops/find.h b/tools/include/asm-generic/bitops/find.h
index eff868bd22f8..382cd80c61aa 100644
--- a/tools/include/asm-generic/bitops/find.h
+++ b/tools/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);
+}
 
 #endif /* find_first_bit */
 
@@ -117,7 +129,17 @@  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.
  */
-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);
+}
 #endif
 
 #endif /*_TOOLS_LINUX_ASM_GENERIC_BITOPS_FIND_H_ */
diff --git a/tools/lib/find_bit.c b/tools/lib/find_bit.c
index c3378b291205..a77884ca30ec 100644
--- a/tools/lib/find_bit.c
+++ b/tools/lib/find_bit.c
@@ -83,7 +83,7 @@  unsigned long _find_next_bit(const unsigned long *addr1,
 /*
  * 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;
 
@@ -100,7 +100,7 @@  unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
 /*
  * 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;