Re: [PATCH] sched/deadline: Use revised wakeup rule only for running dl_server

[Andrea Righi <arighi@nvidia.com>]

Hi Garbiele,

On Fri, May 22, 2026 at 02:58:33PM +0200, Gabriele Monaco wrote:
> Commit 14a857056466 ("sched/deadline: Use revised wakeup rule for
> dl_server") applies the revised wakeup rule to any server, as a result
> servers that are not running (dl_defer_running == 0) and start with a
> deadline overflow get enqueued and can boost tasks as if they were
> running, invalidating the defer rule and the documented state model.
> 
> Apply the revised wakeup rule only for deferrable servers that are
> marked as running.
> 
> Fixes: 14a857056466 ("sched/deadline: Use revised wakeup rule for dl_server")
> Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
> ---
> 
> Tested with ksched_football on a 16 CPUs machine: no regression (1s for
> check in and game over in 10s).
> 
> Apparently the rt_stall sched_ext selftest does fail with tasks not
> always getting above 4% (almost always above 3%). But that seems to be
> the case also before this change on that machine.

Yeah the rt_stall selftest can be a bit flaky sometimes, as long as you get >3%
it's all good, maybe we should relax the min threshold a bit. In any case, I
tested this and it looks good om my side.

Tested-by: Andrea Righi <arighi@nvidia.com>

Thanks,
-Andrea

> 
> ---
>  kernel/sched/deadline.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 7db4c87df83b..e5a7701a8af7 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1017,7 +1017,8 @@ static void update_dl_entity(struct sched_dl_entity *dl_se)
>  	if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
>  	    dl_entity_overflow(dl_se, rq_clock(rq))) {
>  
> -		if (unlikely((!dl_is_implicit(dl_se) || dl_se->dl_defer) &&
> +		if (unlikely((!dl_is_implicit(dl_se) ||
> +			      (dl_se->dl_defer && dl_se->dl_defer_running)) &&
>  			     !dl_time_before(dl_se->deadline, rq_clock(rq)) &&
>  			     !is_dl_boosted(dl_se))) {
>  			update_dl_revised_wakeup(dl_se, rq);
> 
> base-commit: 8bc67e4db64aa72732c474b44ea8622062c903f0
> -- 
> 2.54.0
>