> I still don't understand where the responsiveness came from.
You can get a lot of snappiness from prioritizing GUI processes and lowering the priority of everything else. In modern machines, with lots of cores, you can also try to increase affinity of different interactive processes with a set of cores so that they avoid migrating and losing caches. Finally, Apple is placing low-priority process in the efficient cores and leaving interactive code on the performance ones.
You can get a lot of snappiness from prioritizing GUI processes and lowering the priority of everything else. In modern machines, with lots of cores, you can also try to increase affinity of different interactive processes with a set of cores so that they avoid migrating and losing caches. Finally, Apple is placing low-priority process in the efficient cores and leaving interactive code on the performance ones.