Messages in this thread Patch in this message | | | Date | Thu, 14 Mar 2013 17:24:13 +0100 | From | Oleg Nesterov <> | Subject | Re: + atomic-improve-atomic_inc_unless_negative-atomic_dec_unless_positive .patch added to -mm tree |
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> From: Ming Lei <tom.leiming@gmail.com> > Subject: atomic: improve atomic_inc_unless_negative/atomic_dec_unless_positive > > Generally, both atomic_inc_unless_negative() and > atomic_dec_unless_positive() need at least two atomic_cmpxchg() to > complete the atomic operation. In fact, the 1st atomic_cmpxchg() is just > used to read current value of the atomic variable at most times.
Agreed, this looks ugly...
But can't we make a simpler patch and keep the code simple/readable ?
Oleg.
--- x/include/linux/atomic.h +++ x/include/linux/atomic.h @@ -64,7 +64,7 @@ static inline int atomic_inc_not_zero_hi static inline int atomic_inc_unless_negative(atomic_t *p) { int v, v1; - for (v = 0; v >= 0; v = v1) { + for (v = atomic_read(p); v >= 0; v = v1) { v1 = atomic_cmpxchg(p, v, v + 1); if (likely(v1 == v)) return 1; @@ -77,7 +77,7 @@ static inline int atomic_inc_unless_nega static inline int atomic_dec_unless_positive(atomic_t *p) { int v, v1; - for (v = 0; v <= 0; v = v1) { + for (v = atomic_read(p); v <= 0; v = v1) { v1 = atomic_cmpxchg(p, v, v - 1); if (likely(v1 == v)) return 1;
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