From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Subject: bitmap: use memcmp optimisation in more situations
Commit 7dd968163f ("bitmap: bitmap_equal memcmp optimization") was rather
more restrictive than necessary; we can use memcmp() to implement
bitmap_equal() as long as the number of bits can be proved to be a
multiple of 8. And architectures other than s390 may be able to make good
use of this optimisation.
[arnd@xxxxxxxx: fix build: add a memcmp() declaration]
Link: http://lkml.kernel.org/r/20170630153908.3439707-1-arnd@xxxxxxxx
Link: http://lkml.kernel.org/r/20170628153221.11322-5-willy@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Acked-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/arm/boot/compressed/decompress.c | 1 +
include/linux/bitmap.h | 4 +---
2 files changed, 2 insertions(+), 3 deletions(-)
diff -puN arch/arm/boot/compressed/decompress.c~bitmap-use-memcmp-optimisation-in-more-situations arch/arm/boot/compressed/decompress.c
--- a/arch/arm/boot/compressed/decompress.c~bitmap-use-memcmp-optimisation-in-more-situations
+++ a/arch/arm/boot/compressed/decompress.c
@@ -33,6 +33,7 @@ extern void error(char *);
/* Not needed, but used in some headers pulled in by decompressors */
extern char * strstr(const char * s1, const char *s2);
extern size_t strlen(const char *s);
+extern int memcmp(const void *cs, const void *ct, size_t count);
#ifdef CONFIG_KERNEL_GZIP
#include "../../../../lib/decompress_inflate.c"
diff -puN include/linux/bitmap.h~bitmap-use-memcmp-optimisation-in-more-situations include/linux/bitmap.h
--- a/include/linux/bitmap.h~bitmap-use-memcmp-optimisation-in-more-situations
+++ a/include/linux/bitmap.h
@@ -266,10 +266,8 @@ static inline int bitmap_equal(const uns
{
if (small_const_nbits(nbits))
return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits));
-#ifdef CONFIG_S390
- if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0)
+ if (__builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
return !memcmp(src1, src2, nbits / 8);
-#endif
return __bitmap_equal(src1, src2, nbits);
}
_
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