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Commit a47662b5 authored by Morten Rasmussen's avatar Morten Rasmussen Committed by Chris Redpath
Browse files

ANDROID: sched: Add group_misfit_task load-balance type 



To maximize throughput in systems with asymmetric cpu capacities (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 lower capacity
cpu need to be identified and migrated to a higher capacity cpu if
possible to maximize throughput.

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 one or more 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.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: default avatarMorten Rasmussen <morten.rasmussen@arm.com>
Change-Id: I9e3ccd5c3bde1102e5121c83ec3561cf90b684b7
(fixup for !SMP platforms)
Signed-off-by: default avatarChris Redpath <chris.redpath@arm.com>
parent 6ce1e845

kernel/sched/fair.c

+51 −7
Original line number Diff line number Diff line
@@ -5901,6 +5901,11 @@ static int cpu_util_wake(int cpu, struct task_struct *p) 
	return (util >= capacity) ? capacity : util;

}



static inline int task_fits_capacity(struct task_struct *p, long capacity)

{

	return capacity * 1024 > task_util(p) * capacity_margin;

}



/*

 * Disable WAKE_AFFINE in the case where task @p doesn't fit in the

 * capacity of either the waking CPU @cpu or the previous CPU @prev_cpu.
@@ -5922,7 +5927,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) 
	/* Bring task utilization in sync with prev_cpu */

	sync_entity_load_avg(&p->se);



	return min_cap * 1024 < task_util(p) * capacity_margin;

	return task_fits_capacity(p, min_cap);

}



static bool cpu_overutilized(int cpu)
@@ -6252,6 +6257,29 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ 
		set_last_buddy(se);

}



static inline void update_misfit_task(struct rq *rq, struct task_struct *p)

{

#ifdef CONFIG_SMP

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

#endif

}



static inline void clear_rq_misfit(struct rq *rq)

{

#ifdef CONFIG_SMP

	rq->misfit_task = 0;

#endif

}



static inline unsigned int rq_has_misfit(struct rq *rq)

{

#ifdef CONFIG_SMP

	return rq->misfit_task;

#else

	return 0;

#endif

}



static struct task_struct *

pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)

{
@@ -6342,6 +6370,8 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf 
	if (hrtick_enabled(rq))

		hrtick_start_fair(rq, p);



	update_misfit_task(rq, p);



	return p;

simple:

#endif
@@ -6359,9 +6389,12 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf 
	if (hrtick_enabled(rq))

		hrtick_start_fair(rq, p);



	update_misfit_task(rq, p);



	return p;



idle:

	clear_rq_misfit(rq);

	new_tasks = idle_balance(rq, rf);



	/*
@@ -6567,6 +6600,13 @@ 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
@@ -7079,12 +7119,6 @@ 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

 */
@@ -7100,6 +7134,7 @@ 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;
@@ -7399,6 +7434,9 @@ 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;

}
@@ -7448,6 +7486,10 @@ static inline void update_sg_lb_stats(struct lb_env *env, 
		 */

		if (!nr_running && idle_cpu(i))

			sgs->idle_cpus++;



		if (env->sd->flags & SD_ASYM_CPUCAPACITY &&

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

			sgs->group_misfit_task = capacity_of(i);

	}



	/* Adjust by relative CPU capacity of the group */
@@ -9069,6 +9111,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) 


	if (static_branch_unlikely(&sched_numa_balancing))

		task_tick_numa(rq, curr);



	update_misfit_task(rq, curr);

}



/*

kernel/sched/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -731,6 +731,8 @@ struct rq { 
	struct callback_head *balance_callback;



	unsigned char idle_balance;



	unsigned int misfit_task;

	/* For active balancing */

	int active_balance;

	int push_cpu;