Re: [PATCH v2 10/10] sched/eevdf: Move to a single runqueue

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Peter,

On 5/11/2026 5:01 PM, Peter Zijlstra wrote:
> @@ -9291,34 +9206,25 @@ static void wakeup_preempt_fair(struct r
> +	se = pick_next_entity(rq, true);
> +	if (!se)
> +		goto again;
>  
>  	p = task_of(se);
> -	if (unlikely(throttled))
> +	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
>  		task_throttle_setup_work(p);

I think this bit should also be replicated in set_next_task() after
account_cfs_rq_runtime() since any part of the hierarchy may get
throttled as a result of failing to grab runtime.

Also check_cfs_rq_runtime() only sees if the cfs_rq is throttled
but the task can fail to run if it is on a throttled_hierarchy() too
so that should be the correct check here.

Something like below (only build tested on queue/sched/flat):

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e54da4c6c945..950c072244b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9224,7 +9224,19 @@ struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
 		goto again;
 
 	p = task_of(se);
-	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
+	/*
+	 * For cases where prev is picked again after
+	 * being throttled, entity_tick() would have
+	 * already marked its hierarchy as throttled.
+	 *
+	 * Add throttle work here since
+	 * put_prev_set_next_task() is skipped on
+	 * same task's selection.
+	 *
+	 * For other case, set_next_task_fair() will
+	 * handle adding the throttle work.
+	 */
+	if (throttled_hierarchy(cfs_rq_of(se)))
 		task_throttle_setup_work(p);
 	return p;
 
@@ -13819,6 +13831,12 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 		if (on_rq)
 			weight = __calc_prop_weight(cfs_rq, se, weight);
 	}
+	/*
+	 * Add throttle work if the bandwidth allocation above failed
+	 * to grab any runtime and throttled the task's hierarchy.
+	 */
+	if (throttled_hierarchy(task_cfs_rq(p)))
+		task_throttle_setup_work(p);
 
 	se = &p->se;
 	cfs_rq->curr = se;
---


>  	return p;
>  

-- 
Thanks and Regards,
Prateek