Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test)

Paul E. McKenney
2023-01-21T00:34:42Z

On Sat, Jan 21, 2023 at 01:03:50AM +0100, Jonas Oberhauser wrote:
>
>
> On 1/21/2023 12:19 AM, Paul E. McKenney wrote:
> > On Fri, Jan 20, 2023 at 11:36:15PM +0100, Jonas Oberhauser wrote:
> > >
> > > On 1/20/2023 10:37 PM, Paul E. McKenney wrote:
> > > > Just out of curiosity, are you [set] up to run LKMM locally at your end?
> > > I don't know what exactly that means. I generally run it on wetware.
> > > But I sometimes ask Hernan to run Dat3M (on his machine) over all the litmus
> > > tests in your repo to spot any obvious problems with variations I consider.
> > > I don't think Dat3M is feature-complete with herd at the moment, just
> > > unbelievably faster. For example I think it ignores all flags in the cat
> > > files.
> > > Oh, I just remembered that I also installed herd7 recently to make sure that
> > > any patches I might send in satisfy herd7 syntax requirements (I think you
> > > called this diagnostic driven development?), but I haven't used it to really
> > > run anything.
> > >
> > > Is it too obvious that my words usually aren't backed by cold machine logic?
> > Well, there was this in one of your messages from earlier today: "I'm not
> > going to get it right today, am I?" And I freely confess that this led
> > me to suspect that you might not have been availing yourself of herd7's
> > opinion before posting. ;-)
> The main reason I might usually not consult herd7's opinion is that it often
> takes a while to write a test case in a way herd7 accepts and treats as
> intended, but then even so the fact that some tests pass may just give some
> false confidence when some tricky case is being missed.
> So I find the investment/increased confidence ratio to not yet be at the
> right point to do this when communicating somewhat informally on the mailing
> list, which is already taking quite a bit of my time (but at least I'm
> learning a lot during that time about stuff like RCU/SRCU, history of LKMM,
> etc.).
> If I need to be more confident I'll use herd7 to make sure the syntax is
> correct and as a sanity check, and some paper or Coq proofs to be confident
> in the logic.
>
> If you feel that I'm wasting the lists' time too much by making these kind
> of mistakes, let me know and I'll reconsider.

Not a goal of mine, actually.

The only thing that I will add is that I cheat horribly by creating new
litmus tests by existing ones. ;-)

Thanx, Paul