On Mon, 13 Feb 2017, Paul E. McKenney wrote:
> On Mon, Feb 13, 2017 at 08:14:23PM +0100, Tobias Klausmann wrote:
> > Hi!
> >
> > On Mon, 13 Feb 2017, Paul E. McKenney wrote:
> > > On Mon, Feb 13, 2017 at 01:53:27PM -0500, bob smith wrote:
> > > > On 2/13/17 1:39 PM, Paul E. McKenney wrote:
> > > > > can real DEC Alpha hardware end up with both instances of "r1"
> > > > > having the value 1?
> > > >
> > > > I thought this question reminded me of something, so I found this:
> > > > > https://www.kernel.org/doc/Documentation/memory-barriers.txt
> > > >
> > > > and I pasted in the content - David Howells is one of the authors and
> > > > maybe that is why the question sort of reminded me.
> > > >
> > > > Maybe someone has an update but this is what was said then.
> > >
> > > Well, thank you for pointing me to this, but my question was intended to
> > > check whether or not the words I helped to write in memory-barriers.txt
> > > are in fact accurate. So if you have an SMP DEC Alpha system that you
> > > could provide remote access to, that would be very helpful!
> >
> > I have a 4-cpu ES40. Send me a test program and I'll gladly run
> > it for you.
>
> Andrea, could you please convert the litmus test below and send it to
> Tobias?
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> C auto/C-LB-LRW+OB-Dv
> (*
> * Result: Never
> *
> *)
> {
> }
>
> P0(int *u0, int *x1)
> {
> r1 = READ_ONCE(*u0);
> smp_mb();
> WRITE_ONCE(*x1, 1);
> }
>
>
> P1(int *u0, int *x1)
> {
> r1 = rcu_dereference(*x1);
No, please, not this. It should be:
r1 = READ_ONCE(*x1);
That is, the auto/C-LB-LRW+OB-Ov.litmus test.
> WRITE_ONCE(*u0, r1);
> }
>
> exists
> (0:r1=1 /\ 1:r1=1)
Alan
