Commit 7dd96816 authored May 25, 2016 by Martin Schwidefsky

bitmap: bitmap_equal memcmp optimization



The bitmap_equal function has optimized code for small bitmaps with less
than BITS_PER_LONG bits. For larger bitmaps the out-of-line function
__bitmap_equal is called.

For a constant number of bits divisible by BITS_PER_LONG the memcmp
function can be used. For s390 gcc knows how to optimize this function,
memcmp calls with up to 256 bytes / 2048 bits are translated into a
single instruction.

Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent a9809407

include/linux/bitmap.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -267,6 +267,10 @@ static inline int bitmap_equal(const unsigned long *src1,
		{
		if (small_const_nbits(nbits))
		return ! ((src1 ^ src2) & BITMAP_LAST_WORD_MASK(nbits));
		#ifdef CONFIG_S390
		else if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0)
		return !memcmp(src1, src2, nbits / 8);
		#endif
		else
		return __bitmap_equal(src1, src2, nbits);
		}