[RFC tg_shares_up improvements - v1 02/12] sched: on-demand (active) cfs_rq list

From: pjt
Date: Sat Oct 16 2010 - 00:53:55 EST

From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>

Make certain load-balance actions scale per number of active cgroups
instead of the number of existing cgroups.

This makes wakeup/sleep paths more expensive, but is a win for systems
where the vast majority of existing cgroups are idle.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Paul Turner <pjt@xxxxxxxxxx>

---
kernel/sched.c | 86 +++++++++-------------------------------------------
kernel/sched_fair.c | 46 ++++++++++++++++++++++++---
kernel/sched_rt.c | 24 ++++++++++++++
3 files changed, 79 insertions(+), 77 deletions(-)

Index: kernel/sched.c
===================================================================
--- kernel/sched.c.orig
+++ kernel/sched.c
@@ -344,6 +344,7 @@ struct cfs_rq {
* leaf_cfs_rq_list ties together list of leaf cfs_rq's in a cpu. This
* list is used during load balance.
*/
+ int on_list;
struct list_head leaf_cfs_rq_list;
struct task_group *tg; /* group that "owns" this runqueue */

@@ -1530,7 +1531,7 @@ static unsigned long cpu_avg_load_per_ta

#ifdef CONFIG_FAIR_GROUP_SCHED

-static void update_cfs_load(struct cfs_rq *cfs_rq);
+static void update_cfs_load(struct cfs_rq *cfs_rq, int lb);
static void update_cfs_shares(struct cfs_rq *cfs_rq);

/*
@@ -1553,7 +1554,7 @@ static int tg_shares_up(struct task_grou
raw_spin_lock_irqsave(&rq->lock, flags);

update_rq_clock(rq);
- update_cfs_load(cfs_rq);
+ update_cfs_load(cfs_rq, 1);

load_avg = div64_u64(cfs_rq->load_avg, cfs_rq->load_period+1);
load_avg -= cfs_rq->load_contribution;
@@ -7622,15 +7623,13 @@ static void init_rt_rq(struct rt_rq *rt_

#ifdef CONFIG_FAIR_GROUP_SCHED
static void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
- struct sched_entity *se, int cpu, int add,
+ struct sched_entity *se, int cpu,
struct sched_entity *parent)
{
struct rq *rq = cpu_rq(cpu);
tg->cfs_rq[cpu] = cfs_rq;
init_cfs_rq(cfs_rq, rq);
cfs_rq->tg = tg;
- if (add)
- list_add(&cfs_rq->leaf_cfs_rq_list, &rq->leaf_cfs_rq_list);

tg->se[cpu] = se;
/* se could be NULL for init_task_group */
@@ -7650,7 +7649,7 @@ static void init_tg_cfs_entry(struct tas

#ifdef CONFIG_RT_GROUP_SCHED
static void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
- struct sched_rt_entity *rt_se, int cpu, int add,
+ struct sched_rt_entity *rt_se, int cpu,
struct sched_rt_entity *parent)
{
struct rq *rq = cpu_rq(cpu);
@@ -7659,8 +7658,6 @@ static void init_tg_rt_entry(struct task
init_rt_rq(rt_rq, rq);
rt_rq->tg = tg;
rt_rq->rt_runtime = tg->rt_bandwidth.rt_runtime;
- if (add)
- list_add(&rt_rq->leaf_rt_rq_list, &rq->leaf_rt_rq_list);

tg->rt_se[cpu] = rt_se;
if (!rt_se)
@@ -7769,7 +7766,7 @@ void __init sched_init(void)
* We achieve this by letting init_task_group's tasks sit
* directly in rq->cfs (i.e init_task_group->se[] = NULL).
*/
- init_tg_cfs_entry(&init_task_group, &rq->cfs, NULL, i, 1, NULL);
+ init_tg_cfs_entry(&init_task_group, &rq->cfs, NULL, i, NULL);
#endif
#endif /* CONFIG_FAIR_GROUP_SCHED */

@@ -7777,7 +7774,7 @@ void __init sched_init(void)
#ifdef CONFIG_RT_GROUP_SCHED
INIT_LIST_HEAD(&rq->leaf_rt_rq_list);
#ifdef CONFIG_CGROUP_SCHED
- init_tg_rt_entry(&init_task_group, &rq->rt, NULL, i, 1, NULL);
+ init_tg_rt_entry(&init_task_group, &rq->rt, NULL, i, NULL);
#endif
#endif

@@ -8053,7 +8050,7 @@ int alloc_fair_sched_group(struct task_g
if (!se)
goto err_free_rq;

- init_tg_cfs_entry(tg, cfs_rq, se, i, 0, parent->se[i]);
+ init_tg_cfs_entry(tg, cfs_rq, se, i, parent->se[i]);
}

return 1;
@@ -8084,14 +8081,6 @@ int alloc_fair_sched_group(struct task_g
{
return 1;
}
-
-static inline void register_fair_sched_group(struct task_group *tg, int cpu)
-{
-}
-
-static inline void unregister_fair_sched_group(struct task_group *tg, int cpu)
-{
-}
#endif /* CONFIG_FAIR_GROUP_SCHED */

#ifdef CONFIG_RT_GROUP_SCHED
@@ -8143,7 +8132,7 @@ int alloc_rt_sched_group(struct task_gro
if (!rt_se)
goto err_free_rq;

- init_tg_rt_entry(tg, rt_rq, rt_se, i, 0, parent->rt_se[i]);
+ init_tg_rt_entry(tg, rt_rq, rt_se, i, parent->rt_se[i]);
}

return 1;
@@ -8153,17 +8142,6 @@ int alloc_rt_sched_group(struct task_gro
err:
return 0;
}
-
-static inline void register_rt_sched_group(struct task_group *tg, int cpu)
-{
- list_add_rcu(&tg->rt_rq[cpu]->leaf_rt_rq_list,
- &cpu_rq(cpu)->leaf_rt_rq_list);
-}
-
-static inline void unregister_rt_sched_group(struct task_group *tg, int cpu)
-{
- list_del_rcu(&tg->rt_rq[cpu]->leaf_rt_rq_list);
-}
#else /* !CONFIG_RT_GROUP_SCHED */
static inline void free_rt_sched_group(struct task_group *tg)
{
@@ -8174,14 +8152,6 @@ int alloc_rt_sched_group(struct task_gro
{
return 1;
}
-
-static inline void register_rt_sched_group(struct task_group *tg, int cpu)
-{
-}
-
-static inline void unregister_rt_sched_group(struct task_group *tg, int cpu)
-{
-}
#endif /* CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_CGROUP_SCHED
@@ -8197,7 +8167,6 @@ struct task_group *sched_create_group(st
{
struct task_group *tg;
unsigned long flags;
- int i;

tg = kzalloc(sizeof(*tg), GFP_KERNEL);
if (!tg)
@@ -8210,10 +8179,6 @@ struct task_group *sched_create_group(st
goto err;

spin_lock_irqsave(&task_group_lock, flags);
- for_each_possible_cpu(i) {
- register_fair_sched_group(tg, i);
- register_rt_sched_group(tg, i);
- }
list_add_rcu(&tg->list, &task_groups);

WARN_ON(!parent); /* root should already exist */
@@ -8244,10 +8209,12 @@ void sched_destroy_group(struct task_gro
int i;

spin_lock_irqsave(&task_group_lock, flags);
- for_each_possible_cpu(i) {
- unregister_fair_sched_group(tg, i);
- unregister_rt_sched_group(tg, i);
- }
+ /*
+ * XXX should not be a race against enqueue, even without rq->lock
+ * because only empty groups can be destroyed.
+ */
+ for_each_possible_cpu(i)
+ list_del_leaf_cfs_rq(tg->cfs_rq[i]);
list_del_rcu(&tg->list);
list_del_rcu(&tg->siblings);
spin_unlock_irqrestore(&task_group_lock, flags);
@@ -8325,7 +8292,6 @@ static DEFINE_MUTEX(shares_mutex);
int sched_group_set_shares(struct task_group *tg, unsigned long shares)
{
int i;
- unsigned long flags;

/*
* We can't change the weight of the root cgroup.
@@ -8342,19 +8308,6 @@ int sched_group_set_shares(struct task_g
if (tg->shares == shares)
goto done;

- spin_lock_irqsave(&task_group_lock, flags);
- for_each_possible_cpu(i)
- unregister_fair_sched_group(tg, i);
- list_del_rcu(&tg->siblings);
- spin_unlock_irqrestore(&task_group_lock, flags);
-
- /* wait for any ongoing reference to this group to finish */
- synchronize_sched();
-
- /*
- * Now we are free to modify the group's share on each cpu
- * w/o tripping rebalance_share or load_balance_fair.
- */
tg->shares = shares;
for_each_possible_cpu(i) {
/*
@@ -8363,15 +8316,6 @@ int sched_group_set_shares(struct task_g
set_se_shares(tg->se[i], shares);
}

- /*
- * Enable load balance activity on this group, by inserting it back on
- * each cpu's rq->leaf_cfs_rq_list.
- */
- spin_lock_irqsave(&task_group_lock, flags);
- for_each_possible_cpu(i)
- register_fair_sched_group(tg, i);
- list_add_rcu(&tg->siblings, &tg->parent->children);
- spin_unlock_irqrestore(&task_group_lock, flags);
done:
mutex_unlock(&shares_mutex);
return 0;
Index: kernel/sched_fair.c
===================================================================
--- kernel/sched_fair.c.orig
+++ kernel/sched_fair.c
@@ -143,6 +143,24 @@ static inline struct cfs_rq *cpu_cfs_rq(
return cfs_rq->tg->cfs_rq[this_cpu];
}

+static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
+{
+ if (!cfs_rq->on_list) {
+ list_add_rcu(&cfs_rq->leaf_cfs_rq_list,
+ &rq_of(cfs_rq)->leaf_cfs_rq_list);
+
+ cfs_rq->on_list = 1;
+ }
+}
+
+static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
+{
+ if (cfs_rq->on_list) {
+ list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
+ cfs_rq->on_list = 0;
+ }
+}
+
/* Iterate thr' all leaf cfs_rq's on a runqueue */
#define for_each_leaf_cfs_rq(rq, cfs_rq) \
list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)
@@ -246,6 +264,14 @@ static inline struct cfs_rq *cpu_cfs_rq(
return &cpu_rq(this_cpu)->cfs;
}

+static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
+{
+}
+
+static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
+{
+}
+
#define for_each_leaf_cfs_rq(rq, cfs_rq) \
for (cfs_rq = &rq->cfs; cfs_rq; cfs_rq = NULL)

@@ -648,7 +674,7 @@ account_entity_dequeue(struct cfs_rq *cf
}

#if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
-static void update_cfs_load(struct cfs_rq *cfs_rq)
+static void update_cfs_load(struct cfs_rq *cfs_rq, int lb)
{
u64 period = sched_avg_period();
u64 now, delta;
@@ -673,6 +699,11 @@ static void update_cfs_load(struct cfs_r
cfs_rq->load_period /= 2;
cfs_rq->load_avg /= 2;
}
+
+ if (lb && !cfs_rq->nr_running) {
+ if (cfs_rq->load_avg < (period / 8))
+ list_del_leaf_cfs_rq(cfs_rq);
+ }
}

static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
@@ -719,7 +750,7 @@ static void update_cfs_shares(struct cfs
reweight_entity(cfs_rq_of(se), se, shares);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
-static inline void update_cfs_load(struct cfs_rq *cfs_rq)
+static inline void update_cfs_load(struct cfs_rq *cfs_rq, int lb)
{
}

@@ -849,7 +880,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
* Update run-time statistics of the 'current'.
*/
update_curr(cfs_rq);
- update_cfs_load(cfs_rq);
+ update_cfs_load(cfs_rq, 0);
account_entity_enqueue(cfs_rq, se);
update_cfs_shares(group_cfs_rq(se));

@@ -863,6 +894,9 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
if (se != cfs_rq->curr)
__enqueue_entity(cfs_rq, se);
se->on_rq = 1;
+
+ if (cfs_rq->nr_running == 1)
+ list_add_leaf_cfs_rq(cfs_rq);
}

static void __clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -907,7 +941,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
if (se != cfs_rq->curr)
__dequeue_entity(cfs_rq, se);
se->on_rq = 0;
- update_cfs_load(cfs_rq);
+ update_cfs_load(cfs_rq, 0);
account_entity_dequeue(cfs_rq, se);
update_min_vruntime(cfs_rq);
update_cfs_shares(group_cfs_rq(se));
@@ -1142,7 +1176,7 @@ enqueue_task_fair(struct rq *rq, struct
for_each_sched_entity(se) {
struct cfs_rq *cfs_rq = group_cfs_rq(se);

- update_cfs_load(cfs_rq);
+ update_cfs_load(cfs_rq, 0);
update_cfs_shares(cfs_rq);
}

@@ -1172,7 +1206,7 @@ static void dequeue_task_fair(struct rq
for_each_sched_entity(se) {
struct cfs_rq *cfs_rq = group_cfs_rq(se);

- update_cfs_load(cfs_rq);
+ update_cfs_load(cfs_rq, 0);
update_cfs_shares(cfs_rq);
}

Index: kernel/sched_rt.c
===================================================================
--- kernel/sched_rt.c.orig
+++ kernel/sched_rt.c
@@ -183,6 +183,17 @@ static inline u64 sched_rt_period(struct
return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
}

+static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
+{
+ list_add_rcu(&rt_rq->leaf_rt_rq_list,
+ &rq_of_rt_rq(rt_rq)->leaf_rt_rq_list);
+}
+
+static inline void list_del_leaf_rt_rq(struct rt_rq *rt_rq)
+{
+ list_del_rcu(&rt_rq->leaf_rt_rq_list);
+}
+
#define for_each_leaf_rt_rq(rt_rq, rq) \
list_for_each_entry_rcu(rt_rq, &rq->leaf_rt_rq_list, leaf_rt_rq_list)

@@ -276,6 +287,14 @@ static inline u64 sched_rt_period(struct
return ktime_to_ns(def_rt_bandwidth.rt_period);
}

+static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
+{
+}
+
+static inline void list_del_leaf_rt_rq(struct rt_rq *rt_rq)
+{
+}
+
#define for_each_leaf_rt_rq(rt_rq, rq) \
for (rt_rq = &rq->rt; rt_rq; rt_rq = NULL)

@@ -825,6 +844,9 @@ static void __enqueue_rt_entity(struct s
if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
return;

+ if (!rt_rq->rt_nr_running)
+ list_add_leaf_rt_rq(rt_rq);
+
if (head)
list_add(&rt_se->run_list, queue);
else
@@ -844,6 +866,8 @@ static void __dequeue_rt_entity(struct s
__clear_bit(rt_se_prio(rt_se), array->bitmap);

dec_rt_tasks(rt_se, rt_rq);
+ if (!rt_rq->rt_nr_running)
+ list_del_leaf_rt_rq(rt_rq);
}

/*

--

--
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