The patch titled
Subject: lib/find_bit.c: micro-optimise find_next_*_bit
has been added to the -mm tree. Its filename is
find_bit-micro-optimise-find_next__bit.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/find_bit-micro-optimise-find_next__bit.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/find_bit-micro-optimise-find_next__bit.patch
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------------------------------------------------------
From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Subject: lib/find_bit.c: micro-optimise find_next_*_bit
This saves 20 bytes on my x86-64 build, mostly due to alignment
considerations ... I think it actually saves about five bytes of
instructions. There's really two parts to this commit. First, the first
half of the test: (!nbits || start >= nbits) is trivially a subset of the
second half, since nbits and start are both unsigned. Second, while
looking at the disassembly, I noticed that GCC was predicting the branch
taken. Since this is a failure case, it's clearly the less likely of the
two branches, so add an unlikely() to override GCC's heuristics.
Link: http://lkml.kernel.org/r/1482513603-9630-1-git-send-email-mawilcox@xxxxxxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Acked-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Acked-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/find_bit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN lib/find_bit.c~find_bit-micro-optimise-find_next__bit lib/find_bit.c
--- a/lib/find_bit.c~find_bit-micro-optimise-find_next__bit
+++ a/lib/find_bit.c
@@ -33,7 +33,7 @@ static unsigned long _find_next_bit(cons
{
unsigned long tmp;
- if (!nbits || start >= nbits)
+ if (unlikely(start >= nbits))
return nbits;
tmp = addr[start / BITS_PER_LONG] ^ invert;
_
Patches currently in -mm which might be from mawilcox@xxxxxxxxxxxxx are
find_bit-micro-optimise-find_next__bit.patch
reimplement-idr-and-ida-using-the-radix-tree-support-storing-null-in-the-idr.patch
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