MPI + iso-acoustic self-adjoint jacobian is buggy
Still under investigation.

But the following command:

```
DEVITO_MPI=1 mpirun -n 8 --map-by numa python benchmark.py run -P acoustic_sa -op jacobian -d 152 152 152 -so 4 --tn 1000 --autotune off
```

produces broken norms  (ie != no mpi, or mpirun -n 4 which is instead == no mpi, etc)
diff --git a/benchmarks/user/benchmark.py b/benchmarks/user/benchmark.py
index 21d5c5664..a2fdbe473 100644
--- a/benchmarks/user/benchmark.py
+++ b/benchmarks/user/benchmark.py
@@ -66,7 +66,7 @@ def run_op(solver, operator, **options):
         dm = solver.model.dm
         # Because sometime dm is zero, artificially add a non zero slice
         if dm.data.min() == 0 and dm.data.max() == 0:
-            dm.data[..., np.min([25, dm.shape[-1]//4])] = .1
+            dm.data[..., np.min([25, dm.shape_global[-1]//4])] = .1
         return op(dm, **options)
     elif operator == "jacobian_adjoint":
         # I think we want the forward + gradient call, need to merge retvals
['benchmarks/user/benchmark.py']