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bitops: use try_cmpxchg in set_mask_bits and bit_clear_unless 

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
set_mask_bits and bit_clear_unless.  x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg (and
related move instruction in front of cmpxchg).

Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails, enabling further code simplifications.

Link: https://lkml.kernel.org/r/20220822143851.3290-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2022-08-22 16:38:51 +02:00 committed by Andrew Morton
parent 21490eff12
commit e1d7c7609a
1 changed files with 6 additions and 5 deletions
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11
include/linux/bitops.h
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@ -328,10 +328,10 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
const typeof(*(ptr)) mask__ = (mask), bits__ = (bits); \
typeof(*(ptr)) old__, new__; \
\
old__ = READ_ONCE(*(ptr)); \
do { \
old__ = READ_ONCE(*(ptr)); \
new__ = (old__ & ~mask__) | bits__; \
} while (cmpxchg(ptr, old__, new__) != old__); \
} while (!try_cmpxchg(ptr, &old__, new__)); \
\
old__; \
})
@ -343,11 +343,12 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
const typeof(*(ptr)) clear__ = (clear), test__ = (test);\
typeof(*(ptr)) old__, new__; \
\
old__ = READ_ONCE(*(ptr)); \
do { \
old__ = READ_ONCE(*(ptr)); \
if (old__ & test__) \
break; \
new__ = old__ & ~clear__; \
} while (!(old__ & test__) && \
cmpxchg(ptr, old__, new__) != old__); \
} while (!try_cmpxchg(ptr, &old__, new__)); \
\
!(old__ & test__); \
})