Linux 6.18 sched_ext Preps For Cgroup Sub-Scheduler Support

Written by Michael Larabel in Linux Kernel on 27 September 2025 at 06:05 AM EDT. 5 Comments

The sched_ext scheduler framework that allows creating kernel thread schedulers via BPF programs is ready with some updates for the Linux 6.18 kernel.

Sched_ext for Linux 6.18 is bringing code cleanups, new helpers, some debugging enhancements, and a variety of other improvements.

Also standing out with this sched_ext pull is preparations for cgroup sub-scheduler support.

- Code organization cleanup. Separate internal types and accessors to ext_internal.h to reduce the size of ext.c and improve maintainability.

- Prepare for cgroup sub-scheduler support by adding @sch parameter to various functions and helpers, reorganizing scheduler instance handling, and dropping obsolete helpers like scx_kf_exit() and kf_cpu_valid().

- Add new scx_bpf_cpu_curr() and scx_bpf_locked_rq() BPF helpers to provide safer access patterns with proper RCU protection. scx_bpf_cpu_rq() is deprecated with warnings due to potential race conditions.

- Improve debugging with migration-disabled counter in error state dumps, SCX_EFLAG_INITIALIZED flag, bitfields for warning flags, and other enhancements to help diagnose issues.

- Use cgroup_lock/unlock() for cgroup synchronization instead of scx_cgroup_rwsem based synchronization. This is simpler and allows enable/disable paths to synchronize against cgroup changes independent of the CPU controller.

- rhashtable_lookup() replacement to avoid redundant RCU locking was reverted due to RCU usage warnings. Will be redone once rhashtable is updated to use rcu_dereference_all().

- Other misc updates and fixes including bypass handling improvements, scx_task_iter_relock() improvements, tools/sched_ext updates, and compatibility helpers.

More details on these sched_ext changes prepped for the Linux 6.18 merge window via this pull request.