diff mbox series

[5/6] lib: add fast path for find_next_*_bit()

Message ID 20210121000630.371883-6-yury.norov@gmail.com (mailing list archive)
State New, archived
Headers show
Series lib/find_bit: fast path for small bitmaps | expand

Commit Message

Yury Norov Jan. 21, 2021, 12:06 a.m. UTC 
Similarly to bitmap functions, find_next_*_bit() users will benefit
if we'll handle a case of bitmaps that fit into a single word. In the
very best case, the compiler may replace a function call with a
single ffs or ffz instruction.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
 include/asm-generic/bitops/find.h | 39 +++++++++++++++++++++++++++++++
 include/asm-generic/bitops/le.h   | 28 ++++++++++++++++++++++
 2 files changed, 67 insertions(+)

Comments

Andy Shevchenko Jan. 21, 2021, 10:34 a.m. UTC | #1 
On Wed, Jan 20, 2021 at 04:06:29PM -0800, Yury Norov wrote:
> Similarly to bitmap functions, find_next_*_bit() users will benefit
> if we'll handle a case of bitmaps that fit into a single word. In the
> very best case, the compiler may replace a function call with a
> single ffs or ffz instruction.

> +	if (small_const_nbits(size)) {
> +		unsigned long val;
> +
> +		if (unlikely(offset >= size))
> +			return size;

> +		val = *addr & BITMAP_FIRST_WORD_MASK(offset)
> +				& BITMAP_LAST_WORD_MASK(size);

Seems like a new helper can be introduced (BITS or BITMAP namespace depending
on the decision):

#define	_OFFSET_SIZE_MASK(o,s)					\
	(BITMAP_FIRST_WORD_MASK(o) & BITMAP_LAST_WORD_MASK(s))

		val = *addr & BITMAP_OFFSET_SIZE_MASK(offset, size);

And so on below.

> +		return val ? __ffs(val) : size;
> +	}
diff mbox series

Patch

diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
index 7ad70dab8e93..d45096069011 100644
--- a/include/asm-generic/bitops/find.h
+++ b/include/asm-generic/bitops/find.h
@@ -20,6 +20,18 @@  static inline
 unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
 			    unsigned long offset)
 {
+	if (small_const_nbits(size)) {
+		unsigned long val;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr & BITMAP_FIRST_WORD_MASK(offset)
+				& BITMAP_LAST_WORD_MASK(size);
+
+		return val ? __ffs(val) : size;
+	}
+
 	return _find_next_bit(addr, NULL, size, offset, 0UL, 0);
 }
 #endif
@@ -40,6 +52,18 @@  unsigned long find_next_and_bit(const unsigned long *addr1,
 		const unsigned long *addr2, unsigned long size,
 		unsigned long offset)
 {
+	if (small_const_nbits(size)) {
+		unsigned long val;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr1 & *addr2 & BITMAP_FIRST_WORD_MASK(offset)
+				      & BITMAP_LAST_WORD_MASK(size);
+
+		return val ? __ffs(val) : size;
+	}
+
 	return _find_next_bit(addr1, addr2, size, offset, 0UL, 0);
 }
 #endif
@@ -58,6 +82,21 @@  static inline
 unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
 				 unsigned long offset)
 {
+	if (small_const_nbits(size)) {
+		unsigned long val, idx;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr | ~BITMAP_FIRST_WORD_MASK(offset);
+		if (val == ~0UL)
+			return size;
+
+		idx = ffz(val);
+
+		return idx < size ? idx : size;
+	}
+
 	return _find_next_bit(addr, NULL, size, offset, ~0UL, 0);
 }
 #endif
diff --git a/include/asm-generic/bitops/le.h b/include/asm-generic/bitops/le.h
index 4cf44ea16ec0..f4a76d3d145f 100644
--- a/include/asm-generic/bitops/le.h
+++ b/include/asm-generic/bitops/le.h
@@ -5,6 +5,7 @@ 
 #include <asm/types.h>
 #include <asm/byteorder.h>
 #include <asm-generic/bitops/find.h>
+#include <linux/swab.h>
 
 #if defined(__LITTLE_ENDIAN)
 
@@ -37,6 +38,21 @@  static inline
 unsigned long find_next_zero_bit_le(const void *addr, unsigned
 		long size, unsigned long offset)
 {
+	if (small_const_nbits(size)) {
+		unsigned long val = *(const unsigned long *)addr, idx;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = swab(val) | ~BITMAP_FIRST_WORD_MASK(offset);
+		if (val == ~0UL)
+			return size;
+
+		idx = ffz(val);
+
+		return idx < size ? idx : size;
+	}
+
 	return _find_next_bit(addr, NULL, size, offset, ~0UL, 1);
 }
 #endif
@@ -46,6 +62,18 @@  static inline
 unsigned long find_next_bit_le(const void *addr, unsigned
 		long size, unsigned long offset)
 {
+	if (small_const_nbits(size)) {
+		unsigned long val = *(const unsigned long *)addr;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = swab(val) & BITMAP_FIRST_WORD_MASK(offset)
+				& BITMAP_LAST_WORD_MASK(size);
+
+		return val ? __ffs(val) : size;
+	}
+
 	return _find_next_bit(addr, NULL, size, offset, 0UL, 1);
 }
 #endif