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>
diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
index 72a51e5..1914e97 100644
--- a/include/asm-generic/bitops/find.h
+++ b/include/asm-generic/bitops/find.h
@@ -1,11 +1,13 @@
#ifndef _ASM_GENERIC_BITOPS_FIND_H_
#define _ASM_GENERIC_BITOPS_FIND_H_
+#ifndef CONFIG_GENERIC_FIND_NEXT_BIT
extern unsigned long find_next_bit(const unsigned long *addr, unsigned long
size, unsigned long offset);
extern unsigned long find_next_zero_bit(const unsigned long *addr, unsigned
long size, unsigned long offset);
+#endif
#define find_first_bit(addr, size) find_next_bit((addr), (size), 0)
#define find_first_zero_bit(addr, size) find_next_zero_bit((addr), (size), 0)