Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] bitops: Use try_cmpxchg in set_mask_bits and bit_clear_unless | Date | Mon, 22 Aug 2022 16:38:51 +0200 |
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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.
Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- include/linux/bitops.h | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index cf9bf65039f2..7d1a3b01d1b0 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -327,10 +327,10 @@ 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__; \ }) @@ -342,11 +342,12 @@ 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__); \ }) -- 2.37.1
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