Messages in this thread | | | Date | Tue, 3 Nov 2015 20:16:44 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [GIT PULL] locking changes for v4.4 |
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On Tue, Nov 03, 2015 at 05:30:29PM -0800, Linus Torvalds wrote: > On Tue, Nov 3, 2015 at 3:58 PM, Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > > > I think I'll pull this, but then just make a separate commit to remove > > all the bogus games with "control" dependencies that seem to have no > > basis is reality. > > So the attached is what I committed in my tree. It took much longer to > try to write the rationale than it took to actually remove the > atomic_read_ctrl() functions, and even so I'm not sure how good that > commit message is. But at least it tries to explain what's going on. > > Note the final part of the rationale: > > I may have to eat my words at some point, but in the absense of clear > proof that alpha actually needs this, or indeed even an explanation of > how alpha could _possibly_ need it, I do not believe these functions are > called for. > > And if it turns out that alpha really _does_ need a barrier for this > case, that barrier still should not be "smp_read_barrier_depends()". > We'd have to make up some new speciality barrier just for alpha, along > with the documentation for why it really is necessary.
For whatever it is worth, the patch looks good to me. The reasons I could imagine why we might want to mark control dependencies are things like documentation and tooling, but given that we currently only have a very small number of them, it is hard to argue that this is of immediate concern, if it is ever of concern.
Thanx, Paul
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