Comment by college_physics

The first type is what people used to call "embarrassingly parallel". While it should be easy to have this solved by now across the board (after all most cpus are multicore now), arguably it is still not quite trivial or uniform, depending on which language or stack one works with.

The second case where there is data exchange between tasks is indeed the real challenge as the problem is basically open ended. The MPI approach conceptually can handle many cases but is maybe too much overhead to be the default programming paradigm. Which brings back to the question of low hanging opportunities. Eg He mentions in the book SQL and I think inner loop vectorisation is another example. But those are rather special 'graphs'