The extensible scheduler class (sched_ext) allows the installation of a custom CPU scheduler built as a set of BPF programs. Its merging for the 6.12 kernel release moved the kernel away from the "one scheduler fits all" approach that had been taken until then; now any system can have its own scheduler optimized for its workloads. Within any given machine, though, it's still "one scheduler fits all"; only one scheduler can be loaded for the system as a whole. The sched_ext sub-scheduler patch series from Tejun Heo aims to change that situation by allowing multiple CPU schedulers to run on a single system.