sched_ext: Make core-sched task ordering hierarchy-aware

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With sub-schedulers, tasks of different schedulers routinely share rqs and
SMT siblings, but scx_prio_less() consults ops.core_sched_before() only when
both tasks belong to the same scheduler. Every pair spanning two schedulers
falls back to the default ordering, so no scheduler can express ordering
across a scheduler boundary, including a root over its sub-schedulers'
tasks.

Order a pair spanning schedulers by the nearest common ancestor that
implements ops.core_sched_before(): both tasks are in its subtree, making
this the one op where a scheduler is called on tasks it delegated to its
sub-schedulers and may not be scheduling anymore. Same-scheduler pairs keep
using the owning scheduler's op so a parent never orders inside a subtree it
delegated. The op is skipped when the deciding scheduler is bypassing on
either task's CPU.

Update scx_qmap to fall back to the kernel's default ordering when handed a
delegated task it has no task_ctx for.

Signed-off-by: Tejun Heo <tj@kernel.org>

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This commit is contained in:

Tejun Heo 2026-08-15 13:08:28 -10:00

parent 0ec5dd0669

commit 006dd4d04b

3 changed files with 51 additions and 15 deletions

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38

kernel/sched/ext/ext.c

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5

kernel/sched/ext/internal.h

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23

tools/sched_ext/scx_qmap.bpf.c

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