sched_ext: Add the scx_has_subs static key and gate sub-sched hot paths

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With CONFIG_EXT_SUB_SCHED=y but no sub-scheduler attached - the common case
- hot paths still pay for sub-sched bookkeeping. Gate it behind
__scx_has_subs, a static key counting live sub-schedulers, so that a
root-only system stops paying.

Most conversions are simple skip-if-no-sub tests. scx_idle_notify() is
special - it's a hierarchy walk, so give it a fast path which notifies the
root directly using the same tests as the walk. A pending
SCX_RQ_SUB_IDLE_RENOTIFY can be ignored as no sub can be owed one and the
caller clears the flag either way.

Suggested-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

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This commit is contained in:

Tejun Heo 2026-07-15 13:37:59 -10:00

parent 6ba3bd6f22

commit 8946dbd3aa

5 changed files with 65 additions and 4 deletions

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4

kernel/sched/ext/ext.c

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10

kernel/sched/ext/idle.c

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19

kernel/sched/ext/internal.h

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kernel/sched/ext/sub.c

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kernel/sched/ext/sub.h

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