Investigate prediction time increase over the versions

Version	Exec time of the prediction unit tests (sec)
0.2.0-dev1	7.41
0.2.0-dev2	9.19
0.2.0-dev3	21.14
main (fee9392a)	35.11

We need to investigate where we went wrong in the prediction code.

Edit

We could have a CI job with a simple exec on CPU and GPU and display times.