The patch titled
Subject: lib/find_bit.c: micro-optimise find_next_*_bit
has been removed from the -mm tree. Its filename was
find_bit-micro-optimise-find_next__bit.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Subject: lib/find_bit.c: micro-optimise find_next_*_bit
This saves 32 bytes on my x86-64 build, mostly due to alignment
considerations and sharing more code between find_next_bit and
find_next_zero_bit, but it does save a couple 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.
[mawilcox@xxxxxxxxxxxxx: v2]
Link: http://lkml.kernel.org/r/1483709016-1834-1-git-send-email-mawilcox@xxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1483709016-1834-1-git-send-email-mawilcox@xxxxxxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Acked-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Acked-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/find_bit.c | 4 ++--
tools/lib/find_bit.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
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;
@@ -151,7 +151,7 @@ static unsigned long _find_next_bit_le(c
{
unsigned long tmp;
- if (!nbits || start >= nbits)
+ if (unlikely(start >= nbits))
return nbits;
tmp = addr[start / BITS_PER_LONG] ^ invert;
diff -puN tools/lib/find_bit.c~find_bit-micro-optimise-find_next__bit tools/lib/find_bit.c
--- a/tools/lib/find_bit.c~find_bit-micro-optimise-find_next__bit
+++ a/tools/lib/find_bit.c
@@ -34,7 +34,7 @@ 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
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