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| author |   Uros Bizjak <ubizjak@gmail.com> | 2022-08-22 16:38:51 +0200 |
|---|---|---|
| committer |   Andrew Morton <akpm@linux-foundation.org> | 2022-09-11 21:55:09 -0700 |
| commit | e1d7c7609ae0933b59840390c1b207ac0a925c8b (patch) | |
| tree | 55170982bc11f6e761a136a01649c1ccc5e92d1b | |
| parent | hfs: replace kmap() with kmap_local_page() in btree.c (diff) | |
| download | linux-dev-e1d7c7609ae0933b59840390c1b207ac0a925c8b.tar.xz linux-dev-e1d7c7609ae0933b59840390c1b207ac0a925c8b.zip | |
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>
| -rw-r--r-- | include/linux/bitops.h | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 3b89c64bcfd8..fb24a513d917 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -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__); \ }) |