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Date: Fri, 3 Sep 2010 04:33:35 +0100
From: Paul Turner <pjt@...gle.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Chris Friesen <cfriesen@...tel.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Pierre Bourdon <pbourdon@...ellency.fr>
Subject: Re: [RFC][PATCH 2/3] sched: On-demand cfs_rq list
On Sat, Aug 28, 2010 at 3:30 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 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@...llo.nl>
> ---
> kernel/sched.c | 86 +++++++++-------------------------------------------
> kernel/sched_fair.c | 41 ++++++++++++++++++++++--
> kernel/sched_rt.c | 24 ++++++++++++++
> 3 files changed, 76 insertions(+), 75 deletions(-)
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/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 */
>
> @@ -1529,7 +1530,7 @@ 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);
>
> /*
> @@ -1552,7 +1553,7 @@ 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;
> @@ -7553,15 +7554,13 @@ 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 */
> @@ -7581,7 +7580,7 @@ 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);
> @@ -7590,8 +7589,6 @@ 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)
> @@ -7700,7 +7697,7 @@ 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 */
>
> @@ -7708,7 +7705,7 @@ 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
>
> @@ -7984,7 +7981,7 @@ 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;
> @@ -8015,14 +8012,6 @@ 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
> @@ -8074,7 +8063,7 @@ 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;
> @@ -8084,17 +8073,6 @@ 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)
> {
> @@ -8105,14 +8083,6 @@ 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
> @@ -8128,7 +8098,6 @@ struct task_group *sched_create_group(st
> {
> struct task_group *tg;
> unsigned long flags;
> - int i;
>
> tg = kzalloc(sizeof(*tg), GFP_KERNEL);
> if (!tg)
> @@ -8141,10 +8110,6 @@ 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 */
> @@ -8175,10 +8140,12 @@ 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);
> @@ -8256,7 +8223,6 @@ 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.
> @@ -8273,19 +8239,6 @@ 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) {
> /*
> @@ -8294,15 +8247,6 @@ 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: linux-2.6/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_fair.c
> +++ linux-2.6/kernel/sched_fair.c
> @@ -143,6 +143,23 @@ 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 +263,14 @@ 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 +673,7 @@ account_entity_dequeue(struct cfs_rq *cf
> }
>
> #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)
> {
> u64 period = sched_avg_period();
> u64 now = rq_of(cfs_rq)->clock;
> @@ -668,6 +693,11 @@ 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_period < (period / 8))
> + list_del_leaf_cfs_rq(cfs_rq);
> + }
> }
>
In the case of zero load, load_avg above will decay however
load_period will remain in the range [period/2, period], any entity
that has passed period/8 time will remain on the leaf rq list.
The lb condition could also be relaxed in the dequeue_entity case.
> static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
> @@ -729,7 +759,7 @@ 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)
> {
> }
>
> @@ -859,7 +889,7 @@ 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));
>
> @@ -873,6 +903,9 @@ 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)
> @@ -917,7 +950,7 @@ 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));
> Index: linux-2.6/kernel/sched_rt.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_rt.c
> +++ linux-2.6/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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