Re: [PATCH] x86: generic versions of find_first_(zero_)bit, convert i386

[Alexander van Heukelum <heukelum@mailshack.com>]

x86: generic versions of find_first_(zero_)bit, convert i386

Generic versions of __find_first_bit and __find_first_zero_bit
are introduced as simplified versions of __find_next_bit and
__find_next_zero_bit. Their compilation and use are guarded by
a new config variable GENERIC_FIND_FIRST_BIT.

The generic versions of find_first_bit and find_first_zero_bit
are implemented in terms of the newly introduced __find_first_bit
and __find_first_zero_bit.

This patch does not remove the i386-specific implementation,
but it does switch i386 to use the generic functions by setting
GENERIC_FIND_FIRST_BIT=y for X86_32.

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>


 arch/x86/Kconfig            |    3 ++
 include/asm-x86/bitops_32.h |    2 +
 include/linux/bitops.h      |   34 +++++++++++++++++++++++++
 lib/Makefile                |    1 +
 lib/find_next_bit.c         |   58 +++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 98 insertions(+), 0 deletions(-)

---

> I guess we should keep the bitops.h portions alive for the moment 
> though (surrounded by #ifndef GENERIC_FIND_FIRST_BIT), to make it
> easy for anyone to flip the Kconfig bit around via a oneliner patch
> and do some benchmarking? At least initially - i'm convinced that
> we want the generic versions in the long run. (especially if, as
> your patches do it, the generic code picks up the easy constant
> tests and optimizes them at build time)
>
>        Ingo 

Keeping the old version alive for the moment is fine with me. Here
is a replacement patch that does exactly that. Runs on i386 with
this patch and also with GENERIC_FIND_FIRST_BIT=n.

I'll finish the patches for X86_64 and the constant-size bitmap
optimizations after work.

Greetings,
	Alexander

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6b3626d..fa7d16d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -80,6 +80,9 @@ config GENERIC_BUG
 	def_bool y
 	depends on BUG
 
+config GENERIC_FIND_FIRST_BIT
+	def_bool X86_32
+
 config GENERIC_FIND_NEXT_BIT
 	def_bool y
 
diff --git a/include/asm-x86/bitops_32.h b/include/asm-x86/bitops_32.h
index 3ed64b2..ba2c0de 100644
--- a/include/asm-x86/bitops_32.h
+++ b/include/asm-x86/bitops_32.h
@@ -5,6 +5,7 @@
  * Copyright 1992, Linus Torvalds.
  */
 
+#ifndef CONFIG_GENERIC_FIND_FIRST_BIT
 /**
  * find_first_zero_bit - find the first zero bit in a memory region
  * @addr: The address to start the search at
@@ -59,6 +60,7 @@ static inline unsigned find_first_bit(const unsigned long *addr, unsigned size)
 	}
 	return x;
 }
+#endif
 
 #ifdef __KERNEL__
 
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 3865f2c..355d67b 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -113,6 +113,40 @@ static inline unsigned fls_long(unsigned long l)
 }
 
 #ifdef __KERNEL__
+#ifdef CONFIG_GENERIC_FIND_FIRST_BIT
+extern unsigned long __find_first_bit(const unsigned long *addr,
+		unsigned long size);
+
+/**
+ * find_first_bit - find the first set bit in a memory region
+ * @addr: The address to start the search at
+ * @size: The maximum size to search
+ *
+ * Returns the bit number of the first set bit.
+ */
+static __always_inline unsigned long
+find_first_bit(const unsigned long *addr, unsigned long size)
+{
+	return __find_first_bit(addr, size);
+}
+
+extern unsigned long __find_first_zero_bit(const unsigned long *addr,
+		unsigned long size);
+
+/**
+ * find_first_zero_bit - find the first cleared bit in a memory region
+ * @addr: The address to start the search at
+ * @size: The maximum size to search
+ *
+ * Returns the bit number of the first cleared bit.
+ */
+static __always_inline unsigned long
+find_first_zero_bit(const unsigned long *addr, unsigned long size)
+{
+	return __find_first_zero_bit(addr, size);
+}
+#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
+
 #ifdef CONFIG_GENERIC_FIND_NEXT_BIT
 extern unsigned long __find_next_bit(const unsigned long *addr,
 		unsigned long size, unsigned long offset);
diff --git a/lib/Makefile b/lib/Makefile
index 23de261..14c93e1 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o
 lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
 lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 lib-$(CONFIG_SEMAPHORE_SLEEPERS) += semaphore-sleepers.o
+lib-$(CONFIG_GENERIC_FIND_FIRST_BIT) += find_next_bit.o
 lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
 obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
diff --git a/lib/find_next_bit.c b/lib/find_next_bit.c
index ce94c4c..d3f5784 100644
--- a/lib/find_next_bit.c
+++ b/lib/find_next_bit.c
@@ -16,6 +16,7 @@
 
 #define BITOP_WORD(nr)		((nr) / BITS_PER_LONG)
 
+#ifdef CONFIG_GENERIC_FIND_NEXT_BIT
 /*
  * Find the next set bit in a memory region.
  */
@@ -102,6 +103,63 @@ found_middle:
 	return result + ffz(tmp);
 }
 EXPORT_SYMBOL(__find_next_zero_bit);
+#endif /* CONFIG_GENERIC_FIND_NEXT_BIT */
+
+#ifdef CONFIG_GENERIC_FIND_FIRST_BIT
+/*
+ * Find the first set bit in a memory region.
+ */
+unsigned long __find_first_bit(const unsigned long *addr,
+		unsigned long size)
+{
+	const unsigned long *p = addr;
+	unsigned long result = 0;
+	unsigned long tmp;
+
+	while (size & ~(BITS_PER_LONG-1)) {
+		if ((tmp = *(p++)))
+			goto found;
+		result += BITS_PER_LONG;
+		size -= BITS_PER_LONG;
+	}
+	if (!size)
+		return result;
+
+	tmp = (*p) & (~0UL >> (BITS_PER_LONG - size));
+	if (tmp == 0UL)		/* Are any bits set? */
+		return result + size;	/* Nope. */
+found:
+	return result + __ffs(tmp);
+}
+EXPORT_SYMBOL(__find_first_bit);
+
+/*
+ * Find the first cleared bit in a memory region.
+ */
+unsigned long __find_first_zero_bit(const unsigned long *addr,
+		unsigned long size)
+{
+	const unsigned long *p = addr;
+	unsigned long result = 0;
+	unsigned long tmp;
+
+	while (size & ~(BITS_PER_LONG-1)) {
+		if (~(tmp = *(p++)))
+			goto found;
+		result += BITS_PER_LONG;
+		size -= BITS_PER_LONG;
+	}
+	if (!size)
+		return result;
+
+	tmp = (*p) | (~0UL << size);
+	if (tmp == ~0UL)	/* Are any bits zero? */
+		return result + size;	/* Nope. */
+found:
+	return result + ffz(tmp);
+}
+EXPORT_SYMBOL(__find_first_zero_bit);
+#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
 
 #ifdef __BIG_ENDIAN