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Commit bca5744a authored by Morten Rasmussen's avatar Morten Rasmussen Committed by Quentin Perret
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UPSTREAM: sched/fair: Add 'group_misfit_task' load-balance type 



To maximize throughput in systems with asymmetric CPU capacities (e.g.
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 with high
utilization 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 or imbalanced ('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 avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: gaku.inami.xh@renesas.com
Cc: valentin.schneider@arm.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1530699470-29808-3-git-send-email-morten.rasmussen@arm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
(cherry picked from commit 3b1baa6496e6b7ad016342a9d256bdfb072ce902)
Signed-off-by: default avatarQuentin Perret <quentin.perret@arm.com>

Change-Id: If859d4e275a25e20ca004ed980c6e563e68d74ca
parent b1c506a0

kernel/sched/fair.c

+46 −8
Original line number Diff line number Diff line
@@ -693,6 +693,7 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se) 


static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);

static unsigned long task_h_load(struct task_struct *p);

static unsigned long capacity_of(int cpu);



/* Give new sched_entity start runnable values to heavy its load in infant time */

void init_entity_runnable_average(struct sched_entity *se)
@@ -1456,7 +1457,6 @@ bool should_numa_migrate_memory(struct task_struct *p, struct page * page, 
static unsigned long weighted_cpuload(struct rq *rq);

static unsigned long source_load(int cpu, int type);

static unsigned long target_load(int cpu, int type);

static unsigned long capacity_of(int cpu);



/* Cached statistics for all CPUs within a node */

struct numa_stats {
@@ -3723,6 +3723,29 @@ util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep) 
	WRITE_ONCE(p->se.avg.util_est, ue);

}



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

{

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

}



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

{

	if (!static_branch_unlikely(&sched_asym_cpucapacity))

		return;



	if (!p) {

		rq->misfit_task_load = 0;

		return;

	}



	if (task_fits_capacity(p, capacity_of(cpu_of(rq)))) {

		rq->misfit_task_load = 0;

		return;

	}



	rq->misfit_task_load = task_h_load(p);

}



#else /* CONFIG_SMP */



#define UPDATE_TG	0x0
@@ -3752,6 +3775,7 @@ util_est_enqueue(struct cfs_rq *cfs_rq, struct task_struct *p) {} 
static inline void

util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p,

		 bool task_sleep) {}

static inline void update_misfit_status(struct task_struct *p, struct rq *rq) {}



#endif /* CONFIG_SMP */
@@ -6293,7 +6317,7 @@ 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);

}



/*
@@ -6712,9 +6736,12 @@ done: __maybe_unused; 
	if (hrtick_enabled(rq))

		hrtick_start_fair(rq, p);



	update_misfit_status(p, rq);



	return p;



idle:

	update_misfit_status(NULL, rq);

	new_tasks = idle_balance(rq, rf);



	/*
@@ -6920,6 +6947,13 @@ 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
@@ -7493,12 +7527,6 @@ 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

 */
@@ -7514,6 +7542,7 @@ struct sg_lb_stats { 
	unsigned int group_weight;

	enum group_type group_type;

	int group_no_capacity;

	unsigned long group_misfit_task_load; /* A CPU has a task too big for its capacity */

#ifdef CONFIG_NUMA_BALANCING

	unsigned int nr_numa_running;

	unsigned int nr_preferred_running;
@@ -7806,6 +7835,9 @@ group_type group_classify(struct sched_group *group, 
	if (sg_imbalanced(group))

		return group_imbalanced;



	if (sgs->group_misfit_task_load)

		return group_misfit_task;



	return group_other;

}
@@ -7880,6 +7912,10 @@ 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_load < rq->misfit_task_load)

			sgs->group_misfit_task_load = rq->misfit_task_load;

	}



	/* Adjust by relative CPU capacity of the group */
@@ -9661,6 +9697,8 @@ 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_status(curr, rq);

}



/*

kernel/sched/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -845,6 +845,8 @@ struct rq { 


	unsigned char		idle_balance;



	unsigned long		misfit_task_load;



	/* For active balancing */

	int			active_balance;

	int			push_cpu;