Re: [CPU Hotplug PATCH] Restore Idle task's priority during CPU_DEAD notification

[Ingo Molnar]

* Srivatsa Vaddagiri <vatsa@xxxxxxxxxx> wrote:

> @@ -3569,6 +3569,7 @@ static int migration_call(struct notifie
>  		rq = task_rq_lock(rq->idle, &flags);
>  		deactivate_task(rq->idle, rq);
>  		__setscheduler(rq->idle, SCHED_NORMAL, MAX_PRIO);
> +		rq->idle->prio = MAX_PRIO;
>  		task_rq_unlock(rq, &flags);
>   		BUG_ON(rq->nr_running != 0);

Looks good. A small nit: while your patch creates a perfectly correct
idle thread too, i'd prefer the modified variant below. The
__setscheduler() call is (technically) incorrect because in the
SCHED_NORMAL case the prio should be zero. So it's a bit cleaner to set
up the static priority to MAX_PRIO and then revert the policy to
SCHED_NORMAL via __setscheduler(). Ok?

	Ingo

From: Srivatsa Vaddagiri <vatsa@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>

--- linux/kernel/sched.c.orig	
+++ linux/kernel/sched.c	
@@ -3566,7 +3566,8 @@ static int migration_call(struct notifie
 		/* Idle task back to normal (off runqueue, low prio) */
 		rq = task_rq_lock(rq->idle, &flags);
 		deactivate_task(rq->idle, rq);
-		__setscheduler(rq->idle, SCHED_NORMAL, MAX_PRIO);
+		rq->idle->static_prio = MAX_PRIO;
+		__setscheduler(rq->idle, SCHED_NORMAL, 0);
 		task_rq_unlock(rq, &flags);
  		BUG_ON(rq->nr_running != 0);
 
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