The patch titled
Subject: bitmap: bitmap_equal() memcmp() optimization
has been added to the -mm tree. Its filename is
bitmap-bitmap_equal-memcmp-optimization.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/bitmap-bitmap_equal-memcmp-optimization.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/bitmap-bitmap_equal-memcmp-optimization.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Subject: bitmap: bitmap_equal() memcmp() optimization
bitmap_equal*( 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.
Link: http://lkml.kernel.org/r/201606070837.u578YJKt047781@xxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/bitmap.h | 4 ++++
1 file changed, 4 insertions(+)
diff -puN include/linux/bitmap.h~bitmap-bitmap_equal-memcmp-optimization include/linux/bitmap.h
--- a/include/linux/bitmap.h~bitmap-bitmap_equal-memcmp-optimization
+++ a/include/linux/bitmap.h
@@ -267,6 +267,10 @@ static inline int bitmap_equal(const uns
{
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);
}
_
Patches currently in -mm which might be from schwidefsky@xxxxxxxxxx are
bitmap-bitmap_equal-memcmp-optimization.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
