On Tue, Nov 26, 2013 at 4:39 PM, Paul E. McKenney
<paulmck@xxxxxxxxxxxxxxxxxx> wrote:
>
> Cross-CPU ordering.
Ok, in that case I *suspect* we want an actual "spin_lock_mb()"
primitive, because if we go with the MCS lock approach, it's quite
possible that we find cases where the fast-case is already a barrier
(like it is on x86 by virtue of the locked instruction) but the MCS
case then is not. And then a separate barrier wouldn't be able to make
that kind of judgement.
Or maybe we don't care enough. It *sounds* like on x86, we do probably
already get the cross-cpu case for free, and on other architectures we
may always need the memory barrier, so maybe the whole
"mb_after_spin_lock()" thing is fine.
Ugh.
Linus
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