On Thu, Oct 31, 2013 at 12:11:21PM +0100, Paolo Bonzini wrote: > Il 31/10/2013 07:47, Gleb Natapov ha scritto: > > This looks dubious to me. All other smp_mb__after_* variants are there > > because some atomic operations have different memory barrier semantics on > > different arches, > > It doesn't have to be arches; Of course it doesn't, but it is now :) > unlock APIs typically have release > semantics only, but SRCU is stronger. > Yes the question is if it is by design or implementation detail we should not rely on. > > but srcu_read_unlock() have the same semantics on all > > arches, so smp_mb__after_srcu_read_unlock() becomes > > smp_mb__after_a_function_that_happens_to_have_mb_now_but_may_not_have_in_the_feature(). > > How likely it is that smp_mb() will disappear from srcu_read_unlock() > > (if was added for a reason I guess)? May be we should change documentation > > to say that srcu_read_unlock() is a memory barrier which will reflect > > the reality. > > That would be different from all other unlock APIs. > As long as it is documented... smp_mb__after_srcu_read_unlock() is just a form of documentation anyway right now. I do not have strong objection to smp_mb__after_srcu_read_unlock() though, the improvement is impressive for such a small change. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
