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Commit 4c6a8248 authored by Morten Rasmussen's avatar Morten Rasmussen Committed by Dmitry Shmidt
Browse files

ANDROID: sched: Add group_misfit_task load-balance type 



To maximize throughput in systems with reduced capacity cpus (e.g.
high RT/IRQ load and/or ARM big.LITTLE) load-balancing has to consider
task and cpu utilization as well as per-cpu compute capacity when
load-balancing in addition to the current average load based
load-balancing policy. Tasks that are scheduled on a reduced capacity
cpu need to be identified and migrated to a higher capacity cpu if
possible.

To implement this additional policy an additional group_type
(load-balance scenario) is added: group_misfit_task. This represents
scenarios where a sched_group has tasks that are not suitable for its
per-cpu capacity. group_misfit_task is only considered if the system is
not overloaded in any other way (group_imbalanced or group_overloaded).

Identifying misfit tasks requires the rq lock to be held. To avoid
taking remote rq locks to examine source sched_groups for misfit tasks,
each cpu is responsible for tracking misfit tasks themselves and update
the rq->misfit_task flag. This means checking task utilization when
tasks are scheduled and on sched_tick.

Signed-off-by: default avatarMorten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: default avatarAndres Oportus <andresoportus@google.com>
parent 5cdeb5f0

kernel/sched/fair.c

+22 −7
Original line number Diff line number Diff line
@@ -6421,6 +6421,8 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct pin_cookie c 
	if (hrtick_enabled(rq))

		hrtick_start_fair(rq, p);



	rq->misfit_task = !task_fits_max(p, rq->cpu);



	return p;

simple:

	cfs_rq = &rq->cfs;
@@ -6442,9 +6444,12 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct pin_cookie c 
	if (hrtick_enabled(rq))

		hrtick_start_fair(rq, p);



	rq->misfit_task = !task_fits_max(p, rq->cpu);



	return p;



idle:

	rq->misfit_task = 0;

	/*

	 * This is OK, because current is on_cpu, which avoids it being picked

	 * for load-balance and preemption/IRQs are still disabled avoiding
@@ -6657,6 +6662,13 @@ static unsigned long __read_mostly max_load_balance_interval = HZ/10; 


enum fbq_type { regular, remote, all };



enum group_type {

	group_other = 0,

	group_misfit_task,

	group_imbalanced,

	group_overloaded,

};



#define LBF_ALL_PINNED	0x01

#define LBF_NEED_BREAK	0x02

#define LBF_DST_PINNED  0x04
@@ -7128,12 +7140,6 @@ static unsigned long task_h_load(struct task_struct *p) 


/********** Helpers for find_busiest_group ************************/



enum group_type {

	group_other = 0,

	group_imbalanced,

	group_overloaded,

};



/*

 * sg_lb_stats - stats of a sched_group required for load_balancing

 */
@@ -7149,6 +7155,7 @@ struct sg_lb_stats { 
	unsigned int group_weight;

	enum group_type group_type;

	int group_no_capacity;

	int group_misfit_task; /* A cpu has a task too big for its capacity */

#ifdef CONFIG_NUMA_BALANCING

	unsigned int nr_numa_running;

	unsigned int nr_preferred_running;
@@ -7465,6 +7472,9 @@ group_type group_classify(struct sched_group *group, 
	if (sg_imbalanced(group))

		return group_imbalanced;



	if (sgs->group_misfit_task)

		return group_misfit_task;



	return group_other;

}
@@ -7516,8 +7526,11 @@ static inline void update_sg_lb_stats(struct lb_env *env, 
		if (!nr_running && idle_cpu(i))

			sgs->idle_cpus++;



		if (cpu_overutilized(i))

		if (cpu_overutilized(i)) {

			*overutilized = true;

			if (!sgs->group_misfit_task && rq->misfit_task)

				sgs->group_misfit_task = capacity_of(i);

		}

	}



	/* Adjust by relative CPU capacity of the group */
@@ -9083,6 +9096,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) 


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

		rq->rd->overutilized = true;



	rq->misfit_task = !task_fits_max(curr, rq->cpu);

}



/*

kernel/sched/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -612,6 +612,7 @@ struct rq { 
#endif

	#define CPU_LOAD_IDX_MAX 5

	unsigned long cpu_load[CPU_LOAD_IDX_MAX];

	unsigned int misfit_task;

#ifdef CONFIG_NO_HZ_COMMON

#ifdef CONFIG_SMP

	unsigned long last_load_update_tick;