Commit 3015ef4b authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

sched/core: Make migrate disable and CPU hotplug cooperative 



On CPU unplug tasks which are in a migrate disabled region cannot be pushed
to a different CPU until they returned to migrateable state.

Account the number of tasks on a runqueue which are in a migrate disabled
section and make the hotplug wait mechanism respect that.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Reviewed-by: default avatarDaniel Bristot de Oliveira <bristot@redhat.com>
Link: https://lkml.kernel.org/r/20201023102347.067278757@infradead.org
parent 6d337eab

kernel/sched/core.c

+30 −6
Original line number Diff line number Diff line
@@ -1721,10 +1721,17 @@ static void migrate_disable_switch(struct rq *rq, struct task_struct *p) 


void migrate_disable(void)

{

	if (current->migration_disabled++)

	struct task_struct *p = current;



	if (p->migration_disabled) {

		p->migration_disabled++;

		return;

	}



	barrier();

	preempt_disable();

	this_rq()->nr_pinned++;

	p->migration_disabled = 1;

	preempt_enable();

}

EXPORT_SYMBOL_GPL(migrate_disable);
@@ -1751,6 +1758,7 @@ void migrate_enable(void) 
	 */

	barrier();

	p->migration_disabled = 0;

	this_rq()->nr_pinned--;

	preempt_enable();

}

EXPORT_SYMBOL_GPL(migrate_enable);
@@ -1760,6 +1768,11 @@ static inline bool is_migration_disabled(struct task_struct *p) 
	return p->migration_disabled;

}



static inline bool rq_has_pinned_tasks(struct rq *rq)

{

	return rq->nr_pinned;

}



#endif



/*
@@ -2693,6 +2706,11 @@ static inline bool is_migration_disabled(struct task_struct *p) 
	return false;

}



static inline bool rq_has_pinned_tasks(struct rq *rq)

{

	return false;

}



#endif



static void
@@ -7066,15 +7084,20 @@ static void balance_push(struct rq *rq) 
	 * Both the cpu-hotplug and stop task are in this case and are

	 * required to complete the hotplug process.

	 */

	if (is_per_cpu_kthread(push_task)) {

	if (is_per_cpu_kthread(push_task) || is_migration_disabled(push_task)) {

		/*

		 * If this is the idle task on the outgoing CPU try to wake

		 * up the hotplug control thread which might wait for the

		 * last task to vanish. The rcuwait_active() check is

		 * accurate here because the waiter is pinned on this CPU

		 * and can't obviously be running in parallel.

		 *

		 * On RT kernels this also has to check whether there are

		 * pinned and scheduled out tasks on the runqueue. They

		 * need to leave the migrate disabled section first.

		 */

		if (!rq->nr_running && rcuwait_active(&rq->hotplug_wait)) {

		if (!rq->nr_running && !rq_has_pinned_tasks(rq) &&

		    rcuwait_active(&rq->hotplug_wait)) {

			raw_spin_unlock(&rq->lock);

			rcuwait_wake_up(&rq->hotplug_wait);

			raw_spin_lock(&rq->lock);
@@ -7121,7 +7144,8 @@ static void balance_hotplug_wait(void) 
{

	struct rq *rq = this_rq();



	rcuwait_wait_event(&rq->hotplug_wait, rq->nr_running == 1,

	rcuwait_wait_event(&rq->hotplug_wait,

			   rq->nr_running == 1 && !rq_has_pinned_tasks(rq),

			   TASK_UNINTERRUPTIBLE);

}
@@ -7366,7 +7390,7 @@ int sched_cpu_dying(unsigned int cpu) 
	sched_tick_stop(cpu);



	rq_lock_irqsave(rq, &rf);

	BUG_ON(rq->nr_running != 1);

	BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq));

	rq_unlock_irqrestore(rq, &rf);



	calc_load_migrate(rq);

kernel/sched/sched.h

+4 −0
Original line number Diff line number Diff line
@@ -1053,6 +1053,10 @@ struct rq { 
	/* Must be inspected within a rcu lock section */

	struct cpuidle_state	*idle_state;

#endif



#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)

	unsigned int		nr_pinned;

#endif

};



#ifdef CONFIG_FAIR_GROUP_SCHED