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sched_ext: Documentation: add note about multiple ops.enqueue() calls in a row

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Commit 84b1a0ea0b
("sched_ext: Implement scx_bpf_dsq_reenq() for user DSQs")
introduced the possibility of ops.enqueue() being called multiple times
in a row for the same task without intervening calls to ops.dequeue().
Document this behavior as it may be surprising to some.

Acked-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: Kuba Piecuch <jpiecuch@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Kuba Piecuch 2026-04-20 15:28:47 +00:00 committed by Tejun Heo
parent 41e3312861
commit d722d70a8b
1 changed files with 5 additions and 0 deletions
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Documentation/scheduler/sched-ext.rst
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@ -339,6 +339,11 @@ The following briefly shows how a waking task is scheduled and executed.
leaves (e.g., when ``ops.dispatch()`` moves it to a terminal DSQ, or
on property change / sleep).
Note that ``ops.enqueue()`` can be called multiple times in a row without
an intervening call to ``ops.dequeue()``. This can happen, for example,
when a task on a user-created DSQ is re-enqueued using
``scx_bpf_dsq_reenq()``. The task stays in BPF custody the entire time.
When a task leaves BPF scheduler custody, ``ops.dequeue()`` is invoked.
The dequeue can happen for different reasons, distinguished by flags: