On 07/07, Mathieu Desnoyers wrote:
quoted text
>
> 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.

quoted text
> 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,

quoted text
> 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.

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html