diff options
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/lib/atomic64_32.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/arch/x86/lib/atomic64_32.c b/arch/x86/lib/atomic64_32.c index 5fc1e2caa544..61959627e1e1 100644 --- a/arch/x86/lib/atomic64_32.c +++ b/arch/x86/lib/atomic64_32.c @@ -76,13 +76,22 @@ u64 atomic64_read(atomic64_t *ptr) */ u64 atomic64_add_return(u64 delta, atomic64_t *ptr) { - u64 old_val, new_val; + /* + * Try first with a (probably incorrect) assumption about + * what we have there. We'll do two loops most likely, + * but we'll get an ownership MESI transaction straight away + * instead of a read transaction followed by a + * flush-for-ownership transaction: + */ + u64 old_val, new_val, real_val = 1ULL << 32; do { - old_val = atomic_read(ptr); + old_val = real_val; new_val = old_val + delta; - } while (atomic64_cmpxchg(ptr, old_val, new_val) != old_val); + real_val = atomic64_cmpxchg(ptr, old_val, new_val); + + } while (real_val != old_val); return new_val; } |