bitmap: bitmap_equal memcmp optimization
authorMartin Schwidefsky <schwidefsky@de.ibm.com>
Wed, 25 May 2016 07:32:20 +0000 (09:32 +0200)
committerMartin Schwidefsky <schwidefsky@de.ibm.com>
Mon, 13 Jun 2016 13:58:21 +0000 (15:58 +0200)
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>
include/linux/bitmap.h

index e9b0b9ab07e5a58a14b5ed0648fb879962e2c6c7..27bfc0b631a98373c3af7d3f8878aa75006303ba 100644 (file)
@@ -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);
 }