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Commit addef378 authored by Thara Gopinath's avatar Thara Gopinath Committed by Chris Redpath
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ANDROID: sched: Per-Sched-domain over utilization 



The current implementation of overutilization, aborts energy aware
scheduling if any cpu in the system is over-utilized. This patch introduces
over utilization flag per sched domain level instead of a single flag
system wide.  Load balancing is done at the sched domain where any
of the cpu is over utilized. If energy aware scheduling is
enabled and no cpu in a sched domain is overuttilized,
load balancing is skipped for that sched domain and energy aware
scheduling continues at that level.

The implementation takes advantage of the shared sched_domain structure
that is common across all the sched domains at a level. The new flag
introduced is placed in this structure so that all the sched domains the
same level share the flag. In case of an overutilized cpu, the flag gets
set at level1 sched_domain. The flag at the parent sched_domain level gets
set in either of the two following scenarios.
 1. There is a misfit task in one of the cpu's in this sched_domain.
 2. The total utilization of the domain is greater than the domain capacity

The flag is cleared if no cpu in a sched domain is overutilized.

This implementation still can have corner scenarios with respect to
misfit tasks. For example consider a sched group with n cpus and
n+1 70%utilized tasks. Ideally this is a case for load balance to happen
in a parent sched domain. But neither the total group utilization is
high enough for the load balance to be triggered
in the parent domain nor there is a cpu with a single overutilized task so
that aload balance is triggered in a parent domain. But again this could be
a purely academic sceanrio, as during task wake up these tasks will be placed
more appropriately.

Signed-off-by: default avatarThara Gopinath <thara.gopinath@linaro.org>
Change-Id: I3f327cff4080096a3e58208dd72c9b7f7913cdb2
Signed-off-by: default avatarChris Redpath <chris.redpath@arm.com>
parent 5886acba

include/linux/sched/topology.h

+2 −0
Original line number Diff line number Diff line
@@ -89,6 +89,8 @@ struct sched_domain_shared { 
	atomic_t	ref;

	atomic_t	nr_busy_cpus;

	int		has_idle_cores;



	bool            overutilized;

};



struct sched_domain {

kernel/sched/fair.c

+98 −23
Original line number Diff line number Diff line
@@ -4870,8 +4870,39 @@ static inline void hrtick_update(struct rq *rq) 
}

#endif



#ifdef CONFIG_SMP

static bool cpu_overutilized(int cpu);



static bool sd_overutilized(struct sched_domain *sd)

{

	return sd->shared->overutilized;

}



static void set_sd_overutilized(struct sched_domain *sd)

{

	sd->shared->overutilized = true;

}



static void clear_sd_overutilized(struct sched_domain *sd)

{

	sd->shared->overutilized = false;

}



static inline void update_overutilized_status(struct rq *rq)

{

	struct sched_domain *sd;



	rcu_read_lock();

	sd = rcu_dereference(rq->sd);

	if (sd && !sd_overutilized(sd) &&

	    cpu_overutilized(rq->cpu))

		set_sd_overutilized(sd);

	rcu_read_unlock();

}

#else

#define update_overutilized_status(rq) do {} while (0)

#endif /* CONFIG_SMP */



/*

 * The enqueue_task method is called before nr_running is

 * increased. Here we update the fair scheduling stats and
@@ -4924,9 +4955,8 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) 


	if (!se) {

		add_nr_running(rq, 1);

		if (!task_new && !rq->rd->overutilized &&

		    cpu_overutilized(rq->cpu))

			rq->rd->overutilized = true;

		if (!task_new)

			update_overutilized_status(rq);

	}

	hrtick_update(rq);

}
@@ -6228,8 +6258,6 @@ static int select_energy_cpu_brute(struct task_struct *p, int prev_cpu) 
	unsigned long max_spare = 0;

	struct sched_domain *sd;



	rcu_read_lock();



	sd = rcu_dereference(per_cpu(sd_ea, prev_cpu));



	if (!sd)
@@ -6267,8 +6295,6 @@ static int select_energy_cpu_brute(struct task_struct *p, int prev_cpu) 
	}



unlock:

	rcu_read_unlock();



	if (energy_cpu == prev_cpu && !cpu_overutilized(prev_cpu))

		return prev_cpu;
@@ -6302,10 +6328,15 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f 
			      && cpumask_test_cpu(cpu, &p->cpus_allowed);

	}



	if (energy_aware() && !(cpu_rq(prev_cpu)->rd->overutilized))

		return select_energy_cpu_brute(p, prev_cpu);



	rcu_read_lock();

	sd = rcu_dereference(cpu_rq(prev_cpu)->sd);

	if (energy_aware() && sd && !sd_overutilized(sd)) {

		new_cpu = select_energy_cpu_brute(p, prev_cpu);

		goto unlock;

	}



	sd = NULL;



	for_each_domain(cpu, tmp) {

		if (!(tmp->flags & SD_LOAD_BALANCE))

			break;
@@ -6374,6 +6405,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f 
		}

		/* while loop will break here if sd == NULL */

	}



unlock:

	rcu_read_unlock();



	return new_cpu;
@@ -7495,6 +7528,7 @@ struct sd_lb_stats { 
	unsigned long total_running;

	unsigned long total_load;	/* Total load of all groups in sd */

	unsigned long total_capacity;	/* Total capacity of all groups in sd */

	unsigned long total_util;	/* Total util of all groups in sd */

	unsigned long avg_load;	/* Average load across all groups in sd */



	struct sg_lb_stats busiest_stat;/* Statistics of the busiest group */
@@ -7515,6 +7549,7 @@ static inline void init_sd_lb_stats(struct sd_lb_stats *sds) 
		.total_running = 0UL,

		.total_load = 0UL,

		.total_capacity = 0UL,

		.total_util = 0UL,

		.busiest_stat = {

			.avg_load = 0UL,

			.sum_nr_running = 0,
@@ -7810,7 +7845,7 @@ group_type group_classify(struct sched_group *group, 
static inline void update_sg_lb_stats(struct lb_env *env,

			struct sched_group *group, int load_idx,

			int local_group, struct sg_lb_stats *sgs,

			bool *overload, bool *overutilized)

			bool *overload, bool *overutilized, bool *misfit_task)

{

	unsigned long load;

	int i, nr_running;
@@ -7849,8 +7884,12 @@ static inline void update_sg_lb_stats(struct lb_env *env, 
		    !sgs->group_misfit_task && rq_has_misfit(rq))

			sgs->group_misfit_task = capacity_of(i);



		if (cpu_overutilized(i))

		if (cpu_overutilized(i)) {

			*overutilized = true;



			if (rq_has_misfit(rq))

				*misfit_task = true;

		}

	}



	/* Adjust by relative CPU capacity of the group */
@@ -7997,7 +8036,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd 
	struct sg_lb_stats *local = &sds->local_stat;

	struct sg_lb_stats tmp_sgs;

	int load_idx, prefer_sibling = 0;

	bool overload = false, overutilized = false;

	bool overload = false, overutilized = false, misfit_task = false;



	if (child && child->flags & SD_PREFER_SIBLING)

		prefer_sibling = 1;
@@ -8019,7 +8058,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd 
		}



		update_sg_lb_stats(env, sg, load_idx, local_group, sgs,

						&overload, &overutilized);

						&overload, &overutilized,

						&misfit_task);



		if (local_group)

			goto next_group;
@@ -8051,6 +8091,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd 
		sds->total_running += sgs->sum_nr_running;

		sds->total_load += sgs->group_load;

		sds->total_capacity += sgs->group_capacity;

		sds->total_util += sgs->group_util;



		sg = sg->next;

	} while (sg != env->sd->groups);
@@ -8064,16 +8105,48 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd 
		/* update overload indicator if we are at root domain */

		if (env->dst_rq->rd->overload != overload)

			env->dst_rq->rd->overload = overload;

	}



		/* Update over-utilization (tipping point, U >= 0) indicator */

		if (env->dst_rq->rd->overutilized != overutilized)

			env->dst_rq->rd->overutilized = overutilized;

	} else {

		if (!env->dst_rq->rd->overutilized && overutilized)

			env->dst_rq->rd->overutilized = true;

	if (overutilized)

		set_sd_overutilized(env->sd);

	else

		clear_sd_overutilized(env->sd);



	/*

	 * If there is a misfit task in one cpu in this sched_domain

	 * it is likely that the imbalance cannot be sorted out among

	 * the cpu's in this sched_domain. In this case set the

	 * overutilized flag at the parent sched_domain.

	 */

	if (misfit_task) {

		struct sched_domain *sd = env->sd->parent;



		/*

		 * In case of a misfit task, load balance at the parent

		 * sched domain level will make sense only if the the cpus

		 * have a different capacity. If cpus at a domain level have

		 * the same capacity, the misfit task cannot be well

		 * accomodated	in any of the cpus and there in no point in

		 * trying a load balance at this level

		 */

		while (sd) {

			if (sd->flags & SD_ASYM_CPUCAPACITY) {

				set_sd_overutilized(sd);

				break;

			}

			sd = sd->parent;

		}

	}



	/*

	 * If the domain util is greater that domain capacity, load balancing

	 * needs to be done at the next sched domain level as well.

	 */

	if (lb_sd_parent(env->sd) &&

	    sds->total_capacity * 1024 < sds->total_util * capacity_margin)

		set_sd_overutilized(env->sd->parent);

}



/**

 * check_asym_packing - Check to see if the group is packed into the

 *			sched domain.
@@ -8298,7 +8371,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env) 
	 */

	update_sd_lb_stats(env, &sds);



	if (energy_aware() && !env->dst_rq->rd->overutilized)

	if (energy_aware() && !sd_overutilized(env->sd))

		goto out_balanced;



	local = &sds.local_stat;
@@ -9225,6 +9298,9 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle) 
		}

		max_cost += sd->max_newidle_lb_cost;



		if (energy_aware() && !sd_overutilized(sd))

			continue;



		if (!(sd->flags & SD_LOAD_BALANCE))

			continue;
@@ -9526,8 +9602,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) 


	update_misfit_task(rq, curr);



	if (!rq->rd->overutilized && cpu_overutilized(task_cpu(curr)))

		rq->rd->overutilized = true;

	update_overutilized_status(rq);

}



/*

kernel/sched/sched.h

+0 −3
Original line number Diff line number Diff line
@@ -629,9 +629,6 @@ struct root_domain { 
	/* Indicate more than one runnable task for any CPU */

	bool overload;



	/* Indicate one or more cpus over-utilized (tipping point) */

	bool overutilized;



	/*

	 * The bit corresponding to a CPU gets set here if such CPU has more

	 * than one runnable -deadline task (as it is below for RT tasks).

kernel/sched/topology.c

+4 −8
Original line number Diff line number Diff line
@@ -1273,15 +1273,11 @@ sd_init(struct sched_domain_topology_level *tl, 
		sd->idle_idx = 1;

	}



	/*

	 * For all levels sharing cache; connect a sched_domain_shared

	 * instance.

	 */

	if (sd->flags & SD_SHARE_PKG_RESOURCES) {

	sd->shared = *per_cpu_ptr(sdd->sds, sd_id);

	atomic_inc(&sd->shared->ref);



	if (sd->flags & SD_SHARE_PKG_RESOURCES)

		atomic_set(&sd->shared->nr_busy_cpus, sd_weight);

	}



	sd->private = sdd;