Re: [PATCH 2/3] sched/core: Add ENQUEUE_RQ_SELECTED to indicate whether ->select_task_rq() was called

[David Vernet]

On Fri, Sep 27, 2024 at 01:46:12PM -1000, Tejun Heo wrote:
> During ttwu, ->select_task_rq() can be skipped if only one CPU is allowed or
> migration is disabled. sched_ext schedulers may perform operations such as
> direct dispatch from ->select_task_rq() path and it is useful for them to
> know whether ->select_task_rq() was skipped in the ->enqueue_task() path.
> 
> Currently, sched_ext schedulers are using ENQUEUE_WAKEUP for this purpose
> and end up assuming incorrectly that ->select_task_rq() was called for tasks
> that are bound to a single CPU or migration disabled.
> 
> Make select_task_rq() indicate whether ->select_task_rq() was called by
> setting WF_RQ_SELECTED in *wake_flags and make ttwu_do_activate() map that
> to ENQUEUE_RQ_SELECTED for ->enqueue_task().
> 
> This will be used by sched_ext to fix ->select_task_rq() skip detection.
> 
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>

Acked-by: David Vernet <void@xxxxxxxxxxxxx>

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