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Commit 0e59bdae authored by Kirill Tkhai's avatar Kirill Tkhai Committed by Ingo Molnar
Browse files

sched/fair: Disable runtime_enabled on dying rq 



We kill rq->rd on the CPU_DOWN_PREPARE stage:

	cpuset_cpu_inactive -> cpuset_update_active_cpus -> partition_sched_domains ->
	-> cpu_attach_domain -> rq_attach_root -> set_rq_offline

This unthrottles all throttled cfs_rqs.

But the cpu is still able to call schedule() till

	take_cpu_down->__cpu_disable()

is called from stop_machine.

This case the tasks from just unthrottled cfs_rqs are pickable
in a standard scheduler way, and they are picked by dying cpu.
The cfs_rqs becomes throttled again, and migrate_tasks()
in migration_call skips their tasks (one more unthrottle
in migrate_tasks()->CPU_DYING does not happen, because rq->rd
is already NULL).

Patch sets runtime_enabled to zero. This guarantees, the runtime
is not accounted, and the cfs_rqs won't exceed given
cfs_rq->runtime_remaining = 1, and tasks will be pickable
in migrate_tasks(). runtime_enabled is recalculated again
when rq becomes online again.

Ben Segall also noticed, we always enable runtime in
tg_set_cfs_bandwidth(). Actually, we should do that for online
cpus only. To prevent races with unthrottle_offline_cfs_rqs()
we take get_online_cpus() lock.

Reviewed-by: default avatarBen Segall <bsegall@google.com>
Reviewed-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: default avatarKirill Tkhai <ktkhai@parallels.com>
CC: Konstantin Khorenko <khorenko@parallels.com>
CC: Paul Turner <pjt@google.com>
CC: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1403684382.3462.42.camel@tkhai


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a22b4b01

kernel/sched/core.c

+7 −1
Original line number Diff line number Diff line
@@ -7817,6 +7817,11 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) 
	if (period > max_cfs_quota_period)

		return -EINVAL;



	/*

	 * Prevent race between setting of cfs_rq->runtime_enabled and

	 * unthrottle_offline_cfs_rqs().

	 */

	get_online_cpus();

	mutex_lock(&cfs_constraints_mutex);

	ret = __cfs_schedulable(tg, period, quota);

	if (ret)
@@ -7842,7 +7847,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) 
	}

	raw_spin_unlock_irq(&cfs_b->lock);



	for_each_possible_cpu(i) {

	for_each_online_cpu(i) {

		struct cfs_rq *cfs_rq = tg->cfs_rq[i];

		struct rq *rq = cfs_rq->rq;
@@ -7858,6 +7863,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) 
		cfs_bandwidth_usage_dec();

out_unlock:

	mutex_unlock(&cfs_constraints_mutex);

	put_online_cpus();



	return ret;

}

kernel/sched/fair.c

+22 −0
Original line number Diff line number Diff line
@@ -3798,6 +3798,19 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) 
	hrtimer_cancel(&cfs_b->slack_timer);

}



static void __maybe_unused update_runtime_enabled(struct rq *rq)

{

	struct cfs_rq *cfs_rq;



	for_each_leaf_cfs_rq(rq, cfs_rq) {

		struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;



		raw_spin_lock(&cfs_b->lock);

		cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;

		raw_spin_unlock(&cfs_b->lock);

	}

}



static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)

{

	struct cfs_rq *cfs_rq;
@@ -3811,6 +3824,12 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq) 
		 * there's some valid quota amount

		 */

		cfs_rq->runtime_remaining = 1;

		/*

		 * Offline rq is schedulable till cpu is completely disabled

		 * in take_cpu_down(), so we prevent new cfs throttling here.

		 */

		cfs_rq->runtime_enabled = 0;



		if (cfs_rq_throttled(cfs_rq))

			unthrottle_cfs_rq(cfs_rq);

	}
@@ -3854,6 +3873,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) 
	return NULL;

}

static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}

static inline void update_runtime_enabled(struct rq *rq) {}

static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}



#endif /* CONFIG_CFS_BANDWIDTH */
@@ -7362,6 +7382,8 @@ void trigger_load_balance(struct rq *rq) 
static void rq_online_fair(struct rq *rq)

{

	update_sysctl();



	update_runtime_enabled(rq);

}



static void rq_offline_fair(struct rq *rq)