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SubjectRe: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel locking
On Thu, Jul 30, 2015 at 08:34:52AM -0700, Paul E. McKenney wrote:
> On Thu, Jul 30, 2015 at 04:44:55PM +0200, Peter Zijlstra wrote:

> > If the extra read before the cmpxchg() does not hurt, we should do the
> > same for mutex and make the above redundant.
>
> I am pretty sure that different hardware wants it done differently. :-/

I think that most archs won't notice since any RmW includes a load of
that variable anyhow. The only case where it can matter is if the RmW is
done outside of the normal cache hierarchy -- like on Power, where the
ll/sc bypasses the L1.


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