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Commit 46a745d9 authored by Vincent Guittot's avatar Vincent Guittot Committed by Ingo Molnar
Browse files

sched/fair: Fix unnecessary increase of balance interval 



In case of active balancing, we increase the balance interval to cover
pinned tasks cases not covered by all_pinned logic. Neverthless, the
active migration triggered by asym packing should be treated as the normal
unbalanced case and reset the interval to default value, otherwise active
migration for asym_packing can be easily delayed for hundreds of ms
because of this pinned task detection mechanism.

The same happens to other conditions tested in need_active_balance() like
misfit task and when the capacity of src_cpu is reduced compared to
dst_cpu (see comments in need_active_balance() for details).

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: valentin.schneider@arm.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 4ad4e481

kernel/sched/fair.c

+27 −13
Original line number Diff line number Diff line
@@ -8826,22 +8826,26 @@ static struct rq *find_busiest_queue(struct lb_env *env, 
 */

#define MAX_PINNED_INTERVAL	512



static int need_active_balance(struct lb_env *env)

static inline bool

asym_active_balance(struct lb_env *env)

{

	struct sched_domain *sd = env->sd;



	if (env->idle != CPU_NOT_IDLE) {



	/*

	 * ASYM_PACKING needs to force migrate tasks from busy but

	 * lower priority CPUs in order to pack all tasks in the

	 * highest priority CPUs.

	 */

		if ((sd->flags & SD_ASYM_PACKING) &&

		    sched_asym_prefer(env->dst_cpu, env->src_cpu))

			return 1;

	return env->idle != CPU_NOT_IDLE && (env->sd->flags & SD_ASYM_PACKING) &&

	       sched_asym_prefer(env->dst_cpu, env->src_cpu);

}



static inline bool

voluntary_active_balance(struct lb_env *env)

{

	struct sched_domain *sd = env->sd;



	if (asym_active_balance(env))

		return 1;



	/*

	 * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.

	 * It's worth migrating the task if the src_cpu's capacity is reduced
@@ -8858,6 +8862,16 @@ static int need_active_balance(struct lb_env *env) 
	if (env->src_grp_type == group_misfit_task)

		return 1;



	return 0;

}



static int need_active_balance(struct lb_env *env)

{

	struct sched_domain *sd = env->sd;



	if (voluntary_active_balance(env))

		return 1;



	return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);

}
@@ -9119,7 +9133,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, 
	} else

		sd->nr_balance_failed = 0;



	if (likely(!active_balance)) {

	if (likely(!active_balance) || voluntary_active_balance(&env)) {

		/* We were unbalanced, so reset the balancing interval */

		sd->balance_interval = sd->min_interval;

	} else {