On Thu, Apr 12, 2018 at 01:21:55PM +0200, Andrea Parri wrote:
> On Thu, Apr 12, 2018 at 12:18:13PM +0200, Paolo Bonzini wrote:
> > On 12/04/2018 11:23, Andrea Parri wrote:
> > >>
> > >> - smp_store_mb() is missing
> > >
> > > Good point. In fact, we could add this to the model as well:
> > > following Peter's remark/the generic implementation,
> >
> > Good idea. smp_store_mb() can save some clock cycles in the relatively
> > common idiom
> >
> > write a write b
> > read b read a
> > if (b) if (a)
> > wake 'em we've been woken
> >
> > > Yeah, those 'Ordering is cumulative', 'Ordering propagates' could
> > > mean different things to different readers... IMO, we may even omit
> > > such information; this doc. does not certainly aim for completeness,
> > > after all. OTOH, we ought to refrain from making this doc. an excuse
> > > to transform (what it is really) high-school maths into some black
> > > magic.
> > FWIW, what I miss in explanation.txt (and to some extent in the paper)
> > is a clear pointer to litmus tests that rely on cumulativity and
> > propagation. In the meanwhile I'll send some patches. Thanks for the
> > feedback, as it also helps validating my understanding of the model.
>
> The litmus test that first comes to my mind when I think of cumulativity
> (at least, 'cumulativity' as intended in LKMM) is:
>
> WRC+pooncerelease+rmbonceonce+Once.litmus
Removing the "cumul-fence* ;" from "let prop" does cause this test to be
allowed, so looks plausible.
> for 'propagation', I could mention:
>
> IRIW+mbonceonces+OnceOnce.litmus
And removing the "acyclic pb as propagation" causes this one to be allowed,
so again plausible.
> (both tests are availabe in tools/memory-model/litmus-tests/). It would
> be a nice to mention these properties in the test descriptions, indeed.
Please see below.
Thanx, Paul
> You might find it useful to also visualize the 'valid' executions (with
> the main events/relations) associated to each of these tests; for this,
>
> $ herd7 -conf linux-kernel.cfg litmus-tests/your-test.litmus \
> -show all -gv
>
> (assuming you have 'gv' installed).
------------------------------------------------------------------------
commit 494f11d10dd7d86e4a381cbe79e77f04cb0cee04
Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Date: Thu Apr 12 14:15:57 2018 -0700
EXP tools/memory-model: Flag "cumulativity" and "propagation" tests
This commit flags WRC+pooncerelease+rmbonceonce+Once.litmus as being
forbidden by LKMM cumulativity and IRIW+mbonceonces+OnceOnce.litmus as
being forbidden by LKMM propagation.
Suggested-by: Andrea Parri <andrea.pa...@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
diff --git a/tools/memory-model/litmus-tests/IRIW+mbonceonces+OnceOnce.litmus
b/tools/memory-model/litmus-tests/IRIW+mbonceonces+OnceOnce.litmus
index 50d5db9ea983..98a3716efa37 100644
--- a/tools/memory-model/litmus-tests/IRIW+mbonceonces+OnceOnce.litmus
+++ b/tools/memory-model/litmus-tests/IRIW+mbonceonces+OnceOnce.litmus
@@ -7,7 +7,7 @@ C IRIW+mbonceonces+OnceOnce
* between each pairs of reads. In other words, is smp_mb() sufficient to
* cause two different reading processes to agree on the order of a pair
* of writes, where each write is to a different variable by a different
- * process?
+ * process? This litmus test exercises LKMM's "propagation" rule.
*)
{}
diff --git a/tools/memory-model/litmus-tests/README
b/tools/memory-model/litmus-tests/README
index 6919909bbd0f..178941d2a51a 100644
--- a/tools/memory-model/litmus-tests/README
+++ b/tools/memory-model/litmus-tests/README
@@ -23,7 +23,8 @@ IRIW+mbonceonces+OnceOnce.litmus
between each pairs of reads. In other words, is smp_mb()
sufficient to cause two different reading processes to agree on
the order of a pair of writes, where each write is to a different
- variable by a different process?
+ variable by a different process? This litmus test is an example
+ that is forbidden by LKMM propagation.
IRIW+poonceonces+OnceOnce.litmus
Test of independent reads from independent writes with nothing
@@ -121,6 +122,7 @@ WRC+poonceonces+Once.litmus
WRC+pooncerelease+rmbonceonce+Once.litmus
These two are members of an extension of the MP litmus-test class
in which the first write is moved to a separate process.
+ The second is an example that is forbidden by LKMM cumulativity.
Z6.0+pooncelock+pooncelock+pombonce.litmus
Is the ordering provided by a spin_unlock() and a subsequent
diff --git
a/tools/memory-model/litmus-tests/WRC+pooncerelease+rmbonceonce+Once.litmus
b/tools/memory-model/litmus-tests/WRC+pooncerelease+rmbonceonce+Once.litmus
index 97fcbffde9a0..5bda4784eb34 100644
--- a/tools/memory-model/litmus-tests/WRC+pooncerelease+rmbonceonce+Once.litmus
+++ b/tools/memory-model/litmus-tests/WRC+pooncerelease+rmbonceonce+Once.litmus
@@ -5,7 +5,8 @@ C WRC+pooncerelease+rmbonceonce+Once
*
* This litmus test is an extension of the message-passing pattern, where
* the first write is moved to a separate process. Because it features
- * a release and a read memory barrier, it should be forbidden.
+ * a release and a read memory barrier, it should be forbidden. This
+ * litmus test exercises LKMM cumulativity.
*)
{}
