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sched: Ditch per cgroup task lists for load-balancing
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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: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: pjt@google.com
Link: http://lkml.kernel.org/n/tip-tx8yqydc7eimgq7i4rkc3a4g@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Peter Zijlstra authored and Ingo Molnar committed Mar 1, 2012
1 parent ddcdf6e commit 367456c
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Showing 3 changed files with 80 additions and 109 deletions.
3 changes: 3 additions & 0 deletions kernel/sched/core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down
176 changes: 75 additions & 101 deletions kernel/sched/fair.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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++;
}

Expand All @@ -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--;
}

Expand Down Expand Up @@ -3085,24 +3070,25 @@ 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;

enum cpu_idle_type idle;
unsigned long max_load_move;
unsigned int flags;

unsigned int loop;
unsigned int loop_break;
unsigned int loop_max;
};

/*
Expand Down Expand Up @@ -3208,53 +3194,69 @@ 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;
if (!can_migrate_task(p, env))
continue;

move_task(p, env);
/*
* Right now, this is only the second place move_task()
* is called, so we can safely collect move_task()
* stats here rather than inside move_task().
*/
schedstat_inc(env->sd, lb_gained[env->idle]);
return 1;
}
move_task(p, env);
/*
* Right now, this is only the second place move_task()
* is called, so we can safely collect move_task()
* stats here rather than inside move_task().
*/
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
/*
Expand All @@ -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:
/*
Expand Down Expand Up @@ -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

Expand All @@ -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))
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -4504,6 +4480,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
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);
Expand All @@ -4521,9 +4498,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
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;
}

Expand Down Expand Up @@ -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;
Expand Down
10 changes: 2 additions & 8 deletions kernel/sched/sched.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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).
Expand All @@ -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)
*
Expand Down Expand Up @@ -420,6 +412,8 @@ struct rq {
int cpu;
int online;

struct list_head cfs_tasks;

u64 rt_avg;
u64 age_stamp;
u64 idle_stamp;
Expand Down

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