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    SubjectRe: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock
    On 07/07, Mathieu Desnoyers wrote:
    >
    > As with any optimization (and this is one that adds a semantic that will
    > just grow the memory barrier/locking rule complexity), it should come
    > with performance benchmarks showing real-life improvements.

    Well, the same applies to smp_mb__xxx_atomic_yyy or smp_mb__before_clear_bit.

    Imho the new helper is not worse, and it could be also used by
    try_to_wake_up(), __pollwake(), insert_work() at least.

    > Otherwise I'd recommend sticking to smp_mb() if this execution path is
    > not that critical, or to move to RCU if it's _that_ critical.
    >
    > A valid argument would be if the data structures protected are so
    > complex that RCU is out of question but still the few cycles saved by
    > removing a memory barrier are really significant.

    Not sure I understand how RCU can help,

    > And even then, the
    > proper solution would be more something like a
    > __read_lock()+smp_mb+smp_mb+__read_unlock(), so we get the performance
    > improvements on architectures other than x86 as well.

    Hmm. could you explain what you mean?

    Oleg.



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