Why not force using cpuset feature when a new process is created?

[yf...@mobvoi.com]

Currently(AOSP 8.0), there are four type cpusets in /dev/cpuset, there are: 

background  foreground  system-background  top-app

For most cases, An app's state must belongs to one of them.

But what confuse me is that the frameworks does not force put an app(or, process for precise) to the cpuset which it belongs to.`setSchedulingGroup()` can do this job but I went though the source code and found out this method is not referenced anywhere.

What's more, see this commit: https://android.googlesource.com/device/google/marlin/+/1fe1d7c470943a2c18ad8164ad87e9db52a782a0

The nanohub's writer force it's process run in /dev/cpuset/foreground/tasks in case the nanohub will run on a cpu which is for top app. BUT, if the actual top app is not set in /dev/cpuset/top-app/tasks, then this nanohub effort seems useless because the top app may not run on cpus which is defined in /dev/cpuset/top-app/cpus.

So my question is why not force a process to a cpuset which it belongs to?