On Thu, Jul 05, 2018 at 08:44:10PM +0200, Andrea Parri wrote:
> On Thu, Jul 05, 2018 at 08:38:36PM +0200, Andrea Parri wrote:
> > > No, I'm definitely not pushing for anything stronger. I'm still just
> > > wondering if the name "RCsc" is right for what you described. For
> > > example, Andrea just said this in a parallel email:
> > >
> > > > "RCsc" as ordering everything except for W -> R, without the [extra]
> > > > barriers
> >
> > And I already regret it: the point is, different communities/people have
> > different things in mind when they use terms such as "RCsc" or "ordering"
> > and different communities seems to be represented in LKMM.
> >
> > Really, I don't think that this is simply a matter of naming (personally,
> > I'd be OK with "foo" or whather you suggested below! ;-)). My suggestion
> > would be: "get in there!! ;-) please let's refrain from using terms such
> > as these (_overly_ overloaded) "RCsc" and "order" when talking about MCM
> > let's rather talk, say, about "ppo", "cumul-fence" ...
>
> ... or bare litmus tests!
Validation of changes to the memory model is going to continue to be
an interesting topic, which will probably involve its share of litmus
tests.
Thanx, Paul
> Andrea
>
>
> >
> > Andrea
> >
> >
> > >
> > > If it's "RCsc with exceptions", doesn't it make sense to find a
> > > different name, rather than simply overloading the term "RCsc" with
> > > a subtly different meaning, and hoping nobody gets confused?
> > >
> > > I suppose on x86 and ARM you'd happen to get "true RCsc" anyway, just
> > > due to the way things are currently mapped: LOCKed RMWs and "true RCsc"
> > > instructions, respectively. But on Power and RISC-V, it would really
> > > be more "RCsc with a W->R exception", right?
> > >
> > > In fact, the more I think about it, this doesn't seem to be RCsc at all.
> > > It seems closer to "RCpc plus extra PC ordering between critical
> > > sections". No?
> > >
> > > The synchronization accesses themselves aren't sequentially consistent
> > > with respect to each other under the Power or RISC-V mappings, unless
> > > there's a hwsync in there somewhere that I missed? Or a rule
> > > preventing stw from forwarding to lwarx? Or some other higher-order
> > > effect preventing it from being observed anyway?
> > >
> > > So that's all I'm suggesting here. If you all buy that, maybe "RCpccs"
> > > for "RCpc with processor consistent critical section ordering"?
> > > I don't have a strong opinion on the name itself; I just want to find
> > > a name that's less ambiguous or overloaded.
> > >
> > > Dan
>
