The kernel’s CPU scheduler does its best to make the right decisions for
just about any workload; over the years, it has been extended to better
handle mobile-device scheduling as well. But handset vendors still end up
applying their own patches to the scheduler for the kernels they ship.
Shipping out-of-tree code in this way leads to a certain amount of
criticism from the kernel community but, as
Vincent Donnefort pointed out in his session at the 2020 Power Management and Scheduling
in the Linux Kernel summit (OSPM), those patches are applied for a
reason. He looked at a set of vendor scheduler patches to see why they are
being used.

Source: LWN.net – [$] Evaluating vendor changes to the scheduler