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authorAlexander van Heukelum <heukelum@mailshack.com>2008-03-11 16:17:19 +0100
committerIngo Molnar <mingo@elte.hu>2008-04-26 19:21:16 +0200
commit64970b68d2b3ed32b964b0b30b1b98518fde388e (patch)
tree7d8eb5ea3ab1a841afa0f7ae1c65e7be4a9ca690 /include/linux
parent60b6783a044a55273b637983f52965c2808a6b86 (diff)
x86, generic: optimize find_next_(zero_)bit for small constant-size bitmaps
This moves an optimization for searching constant-sized small bitmaps form x86_64-specific to generic code. On an i386 defconfig (the x86#testing one), the size of vmlinux hardly changes with this applied. I have observed only four places where this optimization avoids a call into find_next_bit: In the functions return_unused_surplus_pages, alloc_fresh_huge_page, and adjust_pool_surplus, this patch avoids a call for a 1-bit bitmap. In __next_cpu a call is avoided for a 32-bit bitmap. That's it. On x86_64, 52 locations are optimized with a minimal increase in code size: Current #testing defconfig: 146 x bsf, 27 x find_next_*bit text data bss dec hex filename 5392637 846592 724424 6963653 6a41c5 vmlinux After removing the x86_64 specific optimization for find_next_*bit: 94 x bsf, 79 x find_next_*bit text data bss dec hex filename 5392358 846592 724424 6963374 6a40ae vmlinux After this patch (making the optimization generic): 146 x bsf, 27 x find_next_*bit text data bss dec hex filename 5392396 846592 724424 6963412 6a40d4 vmlinux [ tglx@linutronix.de: build fixes ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/bitops.h77
1 files changed, 77 insertions, 0 deletions
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 40d54731de7..3865f2c93bd 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -112,4 +112,81 @@ static inline unsigned fls_long(unsigned long l)
return fls64(l);
}
+#ifdef __KERNEL__
+#ifdef CONFIG_GENERIC_FIND_NEXT_BIT
+extern unsigned long __find_next_bit(const unsigned long *addr,
+ unsigned long size, unsigned long offset);
+
+/**
+ * find_next_bit - find the next set bit in a memory region
+ * @addr: The address to base the search on
+ * @offset: The bitnumber to start searching at
+ * @size: The bitmap size in bits
+ */
+static __always_inline unsigned long
+find_next_bit(const unsigned long *addr, unsigned long size,
+ unsigned long offset)
+{
+ unsigned long value;
+
+ /* Avoid a function call if the bitmap size is a constant */
+ /* and not bigger than BITS_PER_LONG. */
+
+ /* insert a sentinel so that __ffs returns size if there */
+ /* are no set bits in the bitmap */
+ if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
+ value = (*addr) & ((~0ul) << offset);
+ value |= (1ul << size);
+ return __ffs(value);
+ }
+
+ /* the result of __ffs(0) is undefined, so it needs to be */
+ /* handled separately */
+ if (__builtin_constant_p(size) && (size == BITS_PER_LONG)) {
+ value = (*addr) & ((~0ul) << offset);
+ return (value == 0) ? BITS_PER_LONG : __ffs(value);
+ }
+
+ /* size is not constant or too big */
+ return __find_next_bit(addr, size, offset);
+}
+
+extern unsigned long __find_next_zero_bit(const unsigned long *addr,
+ unsigned long size, unsigned long offset);
+
+/**
+ * find_next_zero_bit - find the next cleared bit in a memory region
+ * @addr: The address to base the search on
+ * @offset: The bitnumber to start searching at
+ * @size: The bitmap size in bits
+ */
+static __always_inline unsigned long
+find_next_zero_bit(const unsigned long *addr, unsigned long size,
+ unsigned long offset)
+{
+ unsigned long value;
+
+ /* Avoid a function call if the bitmap size is a constant */
+ /* and not bigger than BITS_PER_LONG. */
+
+ /* insert a sentinel so that __ffs returns size if there */
+ /* are no set bits in the bitmap */
+ if (__builtin_constant_p(size) && (size < BITS_PER_LONG)) {
+ value = (~(*addr)) & ((~0ul) << offset);
+ value |= (1ul << size);
+ return __ffs(value);
+ }
+
+ /* the result of __ffs(0) is undefined, so it needs to be */
+ /* handled separately */
+ if (__builtin_constant_p(size) && (size == BITS_PER_LONG)) {
+ value = (~(*addr)) & ((~0ul) << offset);
+ return (value == 0) ? BITS_PER_LONG : __ffs(value);
+ }
+
+ /* size is not constant or too big */
+ return __find_next_zero_bit(addr, size, offset);
+}
+#endif /* CONFIG_GENERIC_FIND_NEXT_BIT */
+#endif /* __KERNEL__ */
#endif