On 21/05/2016 22:42, Emilio G. Cota wrote:
> Commit a0aa44b4 ("include/qemu/atomic.h: default to __atomic functions")
> set all atomics to default (on recent GCC versions) to __atomic primitives.
>
> In the process, the atomic_rcu_read/set were converted to implement
> consume/release semantics, respectively. This is inefficient; for
> correctness and maximum performance we only need an smp_barrier_depends
> for reads, and an smp_wmb for writes. Fix it by using the original
> definition of these two primitives for all compilers.
Indeed most compilers implement consume the same as acquire, which is
inefficient. However, isn't in practice atomic_thread_fence(release) +
atomic_store(relaxed) the same as atomic_store(release)?
Thanks,
Paolo
