Re: [PATCH 1/2] sched/core: Pass ENQUEUE_RQ_SELECTED on initial enqueue

[Tejun Heo <tj@kernel.org>]

On Thu, Nov 12, 2026 at 10:49:34PM +0800, Tao Cui wrote:
> select_task_rq() sets WF_RQ_SELECTED and ttwu_do_activate() maps it to
> ENQUEUE_RQ_SELECTED so enqueue_task_scx() knows whether ops.select_cpu()
> ran. wake_up_new_task() also calls select_task_rq() but activates the
> new task without the flag, so on the fork path ops.enqueue() never sees
> SCX_ENQ_CPU_SELECTED and SCX_EV_SELECT_CPU_FALLBACK never counts a
> fork-path fallback: a misbehaving select_cpu() leaves no trace in the
> counters, and schedulers testing SCX_ENQ_CPU_SELECTED run a redundant
> select_cpu_dfl() on tasks select_cpu() already placed.
>
> Set ENQUEUE_RQ_SELECTED on the initial enqueue when select_task_rq() was
> called, matching the wakeup path. Only sched_ext consumes the flag.
>
> Fixes: 9b671793c7d9 ("sched_ext, scx_qmap: Add and use SCX_ENQ_CPU_SELECTED")
> Signed-off-by: Tao Cui <cuitao@kylinos.cn>

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

Peter, how do you want to route this? I can take it through sched_ext too
given that the flag is only consumed by sched_ext.

Thanks.

--
tejun