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raid5-cache: use try_cmpxchg in r5l_wake_reclaim
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
r5l_wake_reclaim. 86 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. There is no need to re-read the value in the loop.
Note that the value from *ptr should be read using READ_ONCE to prevent
the compiler from merging, refetching or reordering the read.
No functional change intended.
Cc: Song Liu <song@kernel.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Song Liu <song@kernel.org>