Commit 367456c7 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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sched: Ditch per cgroup task lists for load-balancing 



Per cgroup load-balance has numerous problems, chief amongst them that
there is no real sane order in them. So stop pretending it makes sense
and enqueue all tasks on a single list.

This also allows us to more easily fix the fwd progress issue
uncovered by the lock-break stuff. Rotate the list on failure to
migreate and limit the total iterations to nr_running (which with
releasing the lock isn't strictly accurate but close enough).

Also add a filter that skips very light tasks on the first attempt
around the list, this attempts to avoid shooting whole cgroups around
without affecting over balance.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: pjt@google.com
Link: http://lkml.kernel.org/n/tip-tx8yqydc7eimgq7i4rkc3a4g@git.kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent ddcdf6e7

kernel/sched/core.c

+3 −0
Original line number Diff line number Diff line
@@ -6959,6 +6959,9 @@ void __init sched_init(void) 
		rq->online = 0;

		rq->idle_stamp = 0;

		rq->avg_idle = 2*sysctl_sched_migration_cost;



		INIT_LIST_HEAD(&rq->cfs_tasks);



		rq_attach_root(rq, &def_root_domain);

#ifdef CONFIG_NO_HZ

		rq->nohz_flags = 0;

kernel/sched/fair.c

+75 −101
Original line number Diff line number Diff line
@@ -776,29 +776,16 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se) 
 * Scheduling class queueing methods:

 */



#if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED

static void

add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)

{

	cfs_rq->task_weight += weight;

}

#else

static inline void

add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)

{

}

#endif



static void

account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)

{

	update_load_add(&cfs_rq->load, se->load.weight);

	if (!parent_entity(se))

		update_load_add(&rq_of(cfs_rq)->load, se->load.weight);

	if (entity_is_task(se)) {

		add_cfs_task_weight(cfs_rq, se->load.weight);

		list_add(&se->group_node, &cfs_rq->tasks);

	}

#ifdef CONFIG_SMP

	if (entity_is_task(se))

		list_add(&se->group_node, &rq_of(cfs_rq)->cfs_tasks);

#endif

	cfs_rq->nr_running++;

}
@@ -808,10 +795,8 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se) 
	update_load_sub(&cfs_rq->load, se->load.weight);

	if (!parent_entity(se))

		update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);

	if (entity_is_task(se)) {

		add_cfs_task_weight(cfs_rq, -se->load.weight);

	if (entity_is_task(se))

		list_del_init(&se->group_node);

	}

	cfs_rq->nr_running--;

}
@@ -3085,17 +3070,14 @@ static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preemp 
static unsigned long __read_mostly max_load_balance_interval = HZ/10;



#define LBF_ALL_PINNED	0x01

#define LBF_NEED_BREAK	0x02	/* clears into HAD_BREAK */

#define LBF_HAD_BREAK	0x04

#define LBF_HAD_BREAKS	0x0C	/* count HAD_BREAKs overflows into ABORT */

#define LBF_ABORT	0x10

#define LBF_NEED_BREAK	0x02

#define LBF_ABORT	0x04



struct lb_env {

	struct sched_domain	*sd;



	int			src_cpu;

	struct rq		*src_rq;

	struct cfs_rq		*src_cfs_rq;



	int			dst_cpu;

	struct rq		*dst_rq;
@@ -3103,6 +3085,10 @@ struct lb_env { 
	enum cpu_idle_type	idle;

	unsigned long		max_load_move;

	unsigned int		flags;



	unsigned int		loop;

	unsigned int		loop_break;

	unsigned int		loop_max;

};



/*
@@ -3208,13 +3194,10 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) 
static int move_one_task(struct lb_env *env)

{

	struct task_struct *p, *n;

	struct cfs_rq *cfs_rq;



	for_each_leaf_cfs_rq(env->src_rq, cfs_rq) {

		list_for_each_entry_safe(p, n, &cfs_rq->tasks, se.group_node) {

			if (throttled_lb_pair(task_group(p),

					      env->src_cpu, env->dst_cpu))

				break;

	list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {

		if (throttled_lb_pair(task_group(p), env->src_rq->cpu, env->dst_cpu))

			continue;



		if (!can_migrate_task(p, env))

			continue;
@@ -3228,33 +3211,52 @@ static int move_one_task(struct lb_env *env) 
		schedstat_inc(env->sd, lb_gained[env->idle]);

		return 1;

	}

	}



	return 0;

}



static unsigned long task_h_load(struct task_struct *p);



static unsigned long balance_tasks(struct lb_env *env)

{

	int loops = 0, pulled = 0;

	long rem_load_move = env->max_load_move;

	struct task_struct *p, *n;

	unsigned long load;

	int pulled = 0;



	if (env->max_load_move == 0)

		goto out;



	list_for_each_entry_safe(p, n, &env->src_cfs_rq->tasks, se.group_node) {

		if (loops++ > sysctl_sched_nr_migrate) {

	list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {

		env->loop++;

		/* We've more or less seen every task there is, call it quits */

		if (env->loop > env->loop_max) {

			env->flags |= LBF_ABORT;

			break;

		}

		/* take a beather every nr_migrate tasks */

		if (env->loop > env->loop_break) {

			env->loop_break += sysctl_sched_nr_migrate;

			env->flags |= LBF_NEED_BREAK;

			break;

		}



		if ((p->se.load.weight >> 1) > rem_load_move ||

		    !can_migrate_task(p, env))

			continue;

		if (throttled_lb_pair(task_group(p), env->src_rq->cpu,

					env->dst_cpu))

			goto next;



		load = task_h_load(p);

		if (load < 16 && !env->sd->nr_balance_failed)

			goto next;



		if ((load * 2) > rem_load_move)

			goto next;



		if (!can_migrate_task(p, env))

			goto next;



		move_task(p, env);

		pulled++;

		rem_load_move -= p->se.load.weight;

		rem_load_move -= load;



#ifdef CONFIG_PREEMPT

		/*
@@ -3274,6 +3276,10 @@ static unsigned long balance_tasks(struct lb_env *env) 
		 */

		if (rem_load_move <= 0)

			break;



		continue;

next:

		list_move_tail(&p->se.group_node, &env->src_rq->cfs_tasks);

	}

out:

	/*
@@ -3363,65 +3369,33 @@ static int tg_load_down(struct task_group *tg, void *data) 


static void update_h_load(long cpu)

{

	rcu_read_lock();

	walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);

	rcu_read_unlock();

}



static unsigned long load_balance_fair(struct lb_env *env)

static unsigned long task_h_load(struct task_struct *p)

{

	unsigned long max_load_move = env->max_load_move;

	long rem_load_move = env->max_load_move;



	rcu_read_lock();

	update_h_load(cpu_of(env->src_rq));



	for_each_leaf_cfs_rq(env->src_rq, env->src_cfs_rq) {

		unsigned long busiest_h_load = env->src_cfs_rq->h_load;

		unsigned long busiest_weight = env->src_cfs_rq->load.weight;

		u64 rem_load, moved_load;



		if (env->flags & (LBF_NEED_BREAK|LBF_ABORT))

			break;



		/*

		 * empty group or part of a throttled hierarchy

		 */

		if (!env->src_cfs_rq->task_weight)

			continue;



		if (throttled_lb_pair(env->src_cfs_rq->tg,

				      cpu_of(env->src_rq),

				      env->dst_cpu))

			continue;



		rem_load = (u64)rem_load_move * busiest_weight;

		rem_load = div_u64(rem_load, busiest_h_load + 1);



		env->max_load_move = rem_load;



		moved_load = balance_tasks(env);

		if (!moved_load)

			continue;



		moved_load *= busiest_h_load;

		moved_load = div_u64(moved_load, busiest_weight + 1);

	struct cfs_rq *cfs_rq = task_cfs_rq(p);

	unsigned long load;



		rem_load_move -= moved_load;

		if (rem_load_move < 0)

			break;

	}

	rcu_read_unlock();

	load = p->se.load.weight;

	load = div_u64(load * cfs_rq->h_load, cfs_rq->load.weight + 1);



	return max_load_move - rem_load_move;

	return load;

}

#else

static inline void update_shares(int cpu)

{

}



static unsigned long load_balance_fair(struct lb_env *env)

static inline void update_h_load(long cpu)

{

	env->src_cfs_rq = &env->src_rq->cfs;

	return balance_tasks(env);

}



static unsigned long task_h_load(struct task_struct *p)

{

	return p->se.load.weight;

}

#endif
@@ -3437,9 +3411,10 @@ static int move_tasks(struct lb_env *env) 
	unsigned long max_load_move = env->max_load_move;

	unsigned long total_load_moved = 0, load_moved;



	update_h_load(cpu_of(env->src_rq));

	do {

		env->max_load_move = max_load_move - total_load_moved;

		load_moved = load_balance_fair(env);

		load_moved = balance_tasks(env);

		total_load_moved += load_moved;



		if (env->flags & (LBF_NEED_BREAK|LBF_ABORT))
@@ -4464,6 +4439,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, 
		.dst_cpu	= this_cpu,

		.dst_rq		= this_rq,

		.idle		= idle,

		.loop_break	= sysctl_sched_nr_migrate,

	};



	cpumask_copy(cpus, cpu_active_mask);
@@ -4504,6 +4480,7 @@ redo: 
		env.max_load_move = imbalance;

		env.src_cpu = busiest->cpu;

		env.src_rq = busiest;

		env.loop_max = busiest->nr_running;



		local_irq_save(flags);

		double_rq_lock(this_rq, busiest);
@@ -4521,9 +4498,7 @@ redo: 
			goto out_balanced;



		if (env.flags & LBF_NEED_BREAK) {

			env.flags += LBF_HAD_BREAK - LBF_NEED_BREAK;

			if (env.flags & LBF_ABORT)

				goto out_balanced;

			env.flags &= ~LBF_NEED_BREAK;

			goto redo;

		}
@@ -5357,7 +5332,6 @@ static void set_curr_task_fair(struct rq *rq) 
void init_cfs_rq(struct cfs_rq *cfs_rq)

{

	cfs_rq->tasks_timeline = RB_ROOT;

	INIT_LIST_HEAD(&cfs_rq->tasks);

	cfs_rq->min_vruntime = (u64)(-(1LL << 20));

#ifndef CONFIG_64BIT

	cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;

kernel/sched/sched.h

+2 −8
Original line number Diff line number Diff line
@@ -212,9 +212,6 @@ struct cfs_rq { 
	struct rb_root tasks_timeline;

	struct rb_node *rb_leftmost;



	struct list_head tasks;

	struct list_head *balance_iterator;



	/*

	 * 'curr' points to currently running entity on this cfs_rq.

	 * It is set to NULL otherwise (i.e when none are currently running).
@@ -241,11 +238,6 @@ struct cfs_rq { 
	struct task_group *tg;	/* group that "owns" this runqueue */



#ifdef CONFIG_SMP

	/*

	 * the part of load.weight contributed by tasks

	 */

	unsigned long task_weight;



	/*

	 *   h_load = weight * f(tg)

	 *
@@ -420,6 +412,8 @@ struct rq { 
	int cpu;

	int online;



	struct list_head cfs_tasks;



	u64 rt_avg;

	u64 age_stamp;

	u64 idle_stamp;

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