Without branch hints, the very unlikely chance of the loop repeating due to cmpxchg failure is unrolled with gcc-4 that I have tested. Improve this for architectures with a native cas/cmpxchg. llsc archs should try to implement this natively.
Unified · Split
| @@ -225,8 +225,14 @@ static __inline__ int atomic_sub_return(int i, atomic_t *v) · 224 unmodified lines | ||
| 225 | 225 | ({ \ |
| 226 | 226 | int c, old; \ |
| 227 | 227 | c = atomic_read(v); \ |
| 228 | − while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \ | |
| 228 | + for (;;) { \ | |
| 229 | + if (unlikely(c == (u))) \ | |
| 230 | + break; \ | |
| 231 | + old = atomic_cmpxchg((v), c, c + (a)); \ | |
| 232 | + if (likely(old == c)) \ | |
| 233 | + break; \ | |
| 229 | 234 | c = old; \ |
| 235 | + } \ | |
| 230 | 236 | c != (u); \ |
| 231 | 237 | }) |
| 232 | 238 | #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) |
| @@ -95,8 +95,14 @@ ia64_atomic64_sub (__s64 i, atomic64_t *v) · 94 unmodified lines | ||
| 95 | 95 | ({ \ |
| 96 | 96 | int c, old; \ |
| 97 | 97 | c = atomic_read(v); \ |
| 98 | − while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \ | |
| 98 | + for (;;) { \ | |
| 99 | + if (unlikely(c == (u))) \ | |
| 100 | + break; \ | |
| 101 | + old = atomic_cmpxchg((v), c, c + (a)); \ | |
| 102 | + if (likely(old == c)) \ | |
| 103 | + break; \ | |
| 99 | 104 | c = old; \ |
| 105 | + } \ | |
| 100 | 106 | c != (u); \ |
| 101 | 107 | }) |
| 102 | 108 | #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) |
| @@ -175,8 +175,14 @@ static inline void atomic_set_mask(unsigned long mask, unsigned long *v) · 174 unmodified lines | ||
| 175 | 175 | ({ \ |
| 176 | 176 | int c, old; \ |
| 177 | 177 | c = atomic_read(v); \ |
| 178 | − while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \ | |
| 178 | + for (;;) { \ | |
| 179 | + if (unlikely(c == (u))) \ | |
| 180 | + break; \ | |
| 181 | + old = atomic_cmpxchg((v), c, c + (a)); \ | |
| 182 | + if (likely(old == c)) \ | |
| 183 | + break; \ | |
| 179 | 184 | c = old; \ |
| 185 | + } \ | |
| 180 | 186 | c != (u); \ |
| 181 | 187 | }) |
| 182 | 188 | #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) |
| @@ -89,10 +89,15 @@ static __inline__ int atomic_cmpxchg(atomic_t *v, int old, int new) · 88 unmodified lines | ||
| 89 | 89 | static __inline__ int atomic_add_unless(atomic_t *v, int a, int u) |
| 90 | 90 | { |
| 91 | 91 | int c, old; |
| 92 | − | |
| 93 | 92 | c = atomic_read(v); |
| 94 | − while (c != u && (old = atomic_cmpxchg(v, c, c + a)) != c) | |
| 93 | + for (;;) { | |
| 94 | + if (unlikely(c == u)) | |
| 95 | + break; | |
| 96 | + old = atomic_cmpxchg(v, c, c + a); | |
| 97 | + if (likely(old == c)) | |
| 98 | + break; | |
| 95 | 99 | c = old; |
| 100 | + } | |
| 96 | 101 | return c != u; |
| 97 | 102 | } |
| 98 | 103 | |
| @@ -167,10 +172,15 @@ static __inline__ int atomic64_add_unless(atomic64_t *v, · 68 unmodified lines | ||
| 167 | 172 | long long a, long long u) |
| 168 | 173 | { |
| 169 | 174 | long long c, old; |
| 170 | − | |
| 171 | 175 | c = atomic64_read(v); |
| 172 | − while (c != u && (old = atomic64_cmpxchg(v, c, c + a)) != c) | |
| 176 | + for (;;) { | |
| 177 | + if (unlikely(c == u)) | |
| 178 | + break; | |
| 179 | + old = atomic64_cmpxchg(v, c, c + a); | |
| 180 | + if (likely(old == c)) | |
| 181 | + break; | |
| 173 | 182 | c = old; |
| 183 | + } | |
| 174 | 184 | return c != u; |
| 175 | 185 | } |
| 176 | 186 | |
| @@ -78,9 +78,15 @@ extern int atomic64_sub_ret(int, atomic64_t *); · 77 unmodified lines | ||
| 78 | 78 | ({ \ |
| 79 | 79 | int c, old; \ |
| 80 | 80 | c = atomic_read(v); \ |
| 81 | − while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \ | |
| 81 | + for (;;) { \ | |
| 82 | + if (unlikely(c == (u))) \ | |
| 83 | + break; \ | |
| 84 | + old = atomic_cmpxchg((v), c, c + (a)); \ | |
| 85 | + if (likely(old == c)) \ | |
| 86 | + break; \ | |
| 82 | 87 | c = old; \ |
| 83 | − c != (u); \ | |
| 88 | + } \ | |
| 89 | + likely(c != (u)); \ | |
| 84 | 90 | }) |
| 85 | 91 | #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) |
| 86 | 92 | |
| @@ -405,8 +405,14 @@ static __inline__ long atomic64_sub_return(long i, atomic64_t *v) · 404 unmodified lines | ||
| 405 | 405 | ({ \ |
| 406 | 406 | int c, old; \ |
| 407 | 407 | c = atomic_read(v); \ |
| 408 | − while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \ | |
| 408 | + for (;;) { \ | |
| 409 | + if (unlikely(c == (u))) \ | |
| 410 | + break; \ | |
| 411 | + old = atomic_cmpxchg((v), c, c + (a)); \ | |
| 412 | + if (likely(old == c)) \ | |
| 413 | + break; \ | |
| 409 | 414 | c = old; \ |
| 415 | + } \ | |
| 410 | 416 | c != (u); \ |
| 411 | 417 | }) |
| 412 | 418 | #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) |