8915f0c0de
This is motivated by the fact that p_atomic_read and p_atomic_set may somewhat surprisingly not do the right thing in the old version: while stores and loads are de facto atomic at least on x86, the compiler may apply re-ordering and speculation quite liberally. Basically, the old version uses the "relaxed" memory ordering. The new ordering always uses acquire/release ordering. This is the strongest possible memory ordering that doesn't require additional fence instructions on x86. (And the only stronger ordering is "sequentially consistent", which is usually more than you need anyway.) I would feel more comfortable if p_atomic_set/read in the old implementation were at least using volatile loads and stores, but I don't see a way to get there without typeof (which we cannot use here since the code is compiled with -std=c99). Eventually, we should really just move to something that is based on the atomics in C11 / C++11. Acked-by: Marek Olšák <marek.olsak@amd.com> Reviewed-by: Emil Velikov <emil.velikov@collabora.com> |
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