[PATCHSET sched_ext/for-7.3] sched_ext: Update core-sched task ordering for scheduler hierarchies

[Tejun Heo]

Hello,

Core-sched task ordering predates sub-schedulers. scx_prio_less() consults
ops.core_sched_before() only when both tasks belong to the same scheduler,
and the timestamp fallback maintains its own stamp, p->scx.core_sched_at,
under two different stamping rules. This patchset updates core-sched task
ordering for scheduler hierarchies:

- Fix ops.core_sched_before() being invoked with inverted polarity.

- Replace core_sched_at with p->scx.runnable_at which the stall watchdog
  already maintains, so that the fallback follows one wait-tracking rule.
  A running task orders after every waiting task.

- Order a pair of tasks spanning two schedulers by the nearest common
  ancestor which implements ops.core_sched_before().

- Drop a dead core-sched related test in the dequeue path.

This patchset contains the following four patches:

 0001-sched_ext-Fix-inverted-ops.core_sched_before-invocat.patch
 0002-sched_ext-Use-runnable_at-for-the-default-core-sched.patch
 0003-sched_ext-Make-core-sched-task-ordering-hierarchy-aw.patch
 0004-sched_ext-Drop-the-dead-SCX_DEQ_CORE_SCHED_EXEC-test.patch

and is on top of sched_ext/for-7.3 (3167bd3e0c22). The patches are also
available in the following git branch:

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git core-sched-hier

diffstat follows. Thanks.

 include/linux/sched/ext.h      |   3 -
 kernel/sched/ext/ext.c         | 147 +++++++++++++++++------------------------
 kernel/sched/ext/internal.h    |   5 ++
 tools/sched_ext/scx_qmap.bpf.c |  23 +++++--
 4 files changed, 81 insertions(+), 97 deletions(-)

--
tejun