Re: [PATCH -tip 2/3] sched/wake_q: Relax to acquire semantics

From: Paul E. McKenney
Date: Tue Sep 15 2015 - 10:10:31 EST


On Tue, Sep 15, 2015 at 02:48:00PM +0200, Peter Zijlstra wrote:
> On Tue, Sep 15, 2015 at 05:41:42AM -0700, Paul E. McKenney wrote:
> > > Never mind, the PPC people will implement this with lwsync and that is
> > > very much not transitive IIRC.
> >
> > I am probably lost on context, but...
> >
> > It turns out that lwsync is transitive in special cases. One of them
> > is a series of release-acquire pairs, which can extend indefinitely.
> >
> > Does that help in this case?
>
> Probably not, but good to know. I still don't think we want to rely on
> ACQUIRE/RELEASE being transitive in general though.

OK, I will bite... Why not?

Thanx, Paul

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