Re: [patch 03/18] sched: introduce primitives to account for CFS bandwidth tracking

Kamalesh Babulal
2011-07-22T11:14:59Z

* Paul Turner <pjt@google.com> [2011-07-21 09:43:28]:

> In this patch we introduce the notion of CFS bandwidth, partitioned into
> globally unassigned bandwidth, and locally claimed bandwidth.
>
> - The global bandwidth is per task_group, it represents a pool of unclaimed
> bandwidth that cfs_rqs can allocate from.
> - The local bandwidth is tracked per-cfs_rq, this represents allotments from
> the global pool bandwidth assigned to a specific cpu.
>
> Bandwidth is managed via cgroupfs, adding two new interfaces to the cpu subsystem:
> - cpu.cfs_period_us : the bandwidth period in usecs
> - cpu.cfs_quota_us : the cpu bandwidth (in usecs) that this tg will be allowed
> to consume over period above.
>
> Signed-off-by: Paul Turner <pjt@google.com>
> Signed-off-by: Nikhil Rao <ncrao@google.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
>
> ---
> init/Kconfig | 12 +++
> kernel/sched.c | 196 ++++++++++++++++++++++++++++++++++++++++++++++++++--
> kernel/sched_fair.c | 16 ++++
> 3 files changed, 220 insertions(+), 4 deletions(-)
>
> Index: tip/init/Kconfig
> ===================================================================
> --- tip.orig/init/Kconfig
> +++ tip/init/Kconfig
> @@ -715,6 +715,18 @@ config FAIR_GROUP_SCHED
> depends on CGROUP_SCHED
> default CGROUP_SCHED
>
> +config CFS_BANDWIDTH
> + bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
> + depends on EXPERIMENTAL
> + depends on FAIR_GROUP_SCHED
> + default n
> + help
> + This option allows users to define CPU bandwidth rates (limits) for
> + tasks running within the fair group scheduler. Groups with no limit
> + set are considered to be unconstrained and will run with no
> + restriction.
> + See tip/Documentation/scheduler/sched-bwc.txt for more information.
> +
> config RT_GROUP_SCHED
> bool "Group scheduling for SCHED_RR/FIFO"
> depends on EXPERIMENTAL
> Index: tip/kernel/sched.c
> ===================================================================
> --- tip.orig/kernel/sched.c
> +++ tip/kernel/sched.c
> @@ -244,6 +244,14 @@ struct cfs_rq;
>
> static LIST_HEAD(task_groups);
>
> +struct cfs_bandwidth {
> +#ifdef CONFIG_CFS_BANDWIDTH
> + raw_spinlock_t lock;
> + ktime_t period;
> + u64 quota;
> +#endif
> +};
> +
> /* task group related information */
> struct task_group {
> struct cgroup_subsys_state css;
> @@ -275,6 +283,8 @@ struct task_group {
> #ifdef CONFIG_SCHED_AUTOGROUP
> struct autogroup *autogroup;
> #endif
> +
> + struct cfs_bandwidth cfs_bandwidth;
> };
>
> /* task_group_lock serializes the addition/removal of task groups */
> @@ -374,9 +384,48 @@ struct cfs_rq {
>
> unsigned long load_contribution;
> #endif
> +#ifdef CONFIG_CFS_BANDWIDTH
> + int runtime_enabled;
> + s64 runtime_remaining;
> +#endif
> #endif
> };
>
> +#ifdef CONFIG_FAIR_GROUP_SCHED
> +#ifdef CONFIG_CFS_BANDWIDTH
> +static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
> +{
> + return &tg->cfs_bandwidth;
> +}
> +
> +static inline u64 default_cfs_period(void);
> +
> +static void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> +{
> + raw_spin_lock_init(&cfs_b->lock);
> + cfs_b->quota = RUNTIME_INF;
> + cfs_b->period = ns_to_ktime(default_cfs_period());
> +}
> +
> +static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
> +{
> + cfs_rq->runtime_enabled = 0;
> +}
> +
> +static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> +{}
> +#else
> +static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
> +static void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
> +static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
> +
> +static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
> +{
> + return NULL;
> +}
> +#endif /* CONFIG_CFS_BANDWIDTH */
> +#endif /* CONFIG_FAIR_GROUP_SCHED */
> +
> /* Real-Time classes' related field in a runqueue: */
> struct rt_rq {
> struct rt_prio_array active;
> @@ -7795,6 +7844,7 @@ static void init_tg_cfs_entry(struct tas
> tg->cfs_rq[cpu] = cfs_rq;
> init_cfs_rq(cfs_rq, rq);
> cfs_rq->tg = tg;
> + init_cfs_rq_runtime(cfs_rq);

this hunk fails to apply, due to the changes introduced by
acb5a9ba3bd7 in the tip tree.
>
> tg->se[cpu] = se;
> /* se could be NULL for root_task_group */
> @@ -7930,6 +7980,7 @@ void __init sched_init(void)
> * We achieve this by letting root_task_group's tasks sit
> * directly in rq->cfs (i.e root_task_group->se[] = NULL).
> */
> + init_cfs_bandwidth(&root_task_group.cfs_bandwidth);
> init_tg_cfs_entry(&root_task_group, &rq->cfs, NULL, i, NULL);
> #endif /* CONFIG_FAIR_GROUP_SCHED */
>
> @@ -8171,6 +8222,8 @@ static void free_fair_sched_group(struct
> {
> int i;
>
> + destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));
> +
> for_each_possible_cpu(i) {
> if (tg->cfs_rq)
> kfree(tg->cfs_rq[i]);
> @@ -8198,6 +8251,8 @@ int alloc_fair_sched_group(struct task_g
>
> tg->shares = NICE_0_LOAD;
>
> + init_cfs_bandwidth(tg_cfs_bandwidth(tg));
> +
> for_each_possible_cpu(i) {
> cfs_rq = kzalloc_node(sizeof(struct cfs_rq),
> GFP_KERNEL, cpu_to_node(i));
> @@ -8569,7 +8624,7 @@ static int __rt_schedulable(struct task_
> return walk_tg_tree(tg_schedulable, tg_nop, &data);
> }
>
> -static int tg_set_bandwidth(struct task_group *tg,
> +static int tg_set_rt_bandwidth(struct task_group *tg,
> u64 rt_period, u64 rt_runtime)
> {
> int i, err = 0;
> @@ -8608,7 +8663,7 @@ int sched_group_set_rt_runtime(struct ta
> if (rt_runtime_us < 0)
> rt_runtime = RUNTIME_INF;
>
> - return tg_set_bandwidth(tg, rt_period, rt_runtime);
> + return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
> }
>
> long sched_group_rt_runtime(struct task_group *tg)
> @@ -8633,7 +8688,7 @@ int sched_group_set_rt_period(struct tas
> if (rt_period == 0)
> return -EINVAL;
>
> - return tg_set_bandwidth(tg, rt_period, rt_runtime);
> + return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
> }
>
> long sched_group_rt_period(struct task_group *tg)
> @@ -8823,6 +8878,128 @@ static u64 cpu_shares_read_u64(struct cg
>
> return (u64) scale_load_down(tg->shares);
> }
> +
> +#ifdef CONFIG_CFS_BANDWIDTH
> +const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */
> +const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */
> +
> +static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
> +{
> + int i;
> + struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
> + static DEFINE_MUTEX(mutex);
> +
> + if (tg == &root_task_group)
> + return -EINVAL;
> +
> + /*
> + * Ensure we have at some amount of bandwidth every period. This is
> + * to prevent reaching a state of large arrears when throttled via
> + * entity_tick() resulting in prolonged exit starvation.
> + */
> + if (quota < min_cfs_quota_period || period < min_cfs_quota_period)
> + return -EINVAL;
> +
> + /*
> + * Likewise, bound things on the otherside by preventing insane quota
> + * periods. This also allows us to normalize in computing quota
> + * feasibility.
> + */
> + if (period > max_cfs_quota_period)
> + return -EINVAL;
> +
> + mutex_lock(&mutex);
> + raw_spin_lock_irq(&cfs_b->lock);
> + cfs_b->period = ns_to_ktime(period);
> + cfs_b->quota = quota;
> + raw_spin_unlock_irq(&cfs_b->lock);
> +
> + for_each_possible_cpu(i) {
> + struct cfs_rq *cfs_rq = tg->cfs_rq[i];
> + struct rq *rq = rq_of(cfs_rq);
> +
> + raw_spin_lock_irq(&rq->lock);
> + cfs_rq->runtime_enabled = quota != RUNTIME_INF;
> + cfs_rq->runtime_remaining = 0;
> + raw_spin_unlock_irq(&rq->lock);
> + }
> + mutex_unlock(&mutex);
> +
> + return 0;
> +}
> +
> +int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)
> +{
> + u64 quota, period;
> +
> + period = ktime_to_ns(tg_cfs_bandwidth(tg)->period);
> + if (cfs_quota_us < 0)
> + quota = RUNTIME_INF;
> + else
> + quota = (u64)cfs_quota_us * NSEC_PER_USEC;
> +
> + return tg_set_cfs_bandwidth(tg, period, quota);
> +}
> +
> +long tg_get_cfs_quota(struct task_group *tg)
> +{
> + u64 quota_us;
> +
> + if (tg_cfs_bandwidth(tg)->quota == RUNTIME_INF)
> + return -1;
> +
> + quota_us = tg_cfs_bandwidth(tg)->quota;
> + do_div(quota_us, NSEC_PER_USEC);
> +
> + return quota_us;
> +}
> +
> +int tg_set_cfs_period(struct task_group *tg, long cfs_period_us)
> +{
> + u64 quota, period;
> +
> + period = (u64)cfs_period_us * NSEC_PER_USEC;
> + quota = tg_cfs_bandwidth(tg)->quota;
> +
> + if (period <= 0)
> + return -EINVAL;
> +
> + return tg_set_cfs_bandwidth(tg, period, quota);
> +}
> +
> +long tg_get_cfs_period(struct task_group *tg)
> +{
> + u64 cfs_period_us;
> +
> + cfs_period_us = ktime_to_ns(tg_cfs_bandwidth(tg)->period);
> + do_div(cfs_period_us, NSEC_PER_USEC);
> +
> + return cfs_period_us;
> +}
> +
> +static s64 cpu_cfs_quota_read_s64(struct cgroup *cgrp, struct cftype *cft)
> +{
> + return tg_get_cfs_quota(cgroup_tg(cgrp));
> +}
> +
> +static int cpu_cfs_quota_write_s64(struct cgroup *cgrp, struct cftype *cftype,
> + s64 cfs_quota_us)
> +{
> + return tg_set_cfs_quota(cgroup_tg(cgrp), cfs_quota_us);
> +}
> +
> +static u64 cpu_cfs_period_read_u64(struct cgroup *cgrp, struct cftype *cft)
> +{
> + return tg_get_cfs_period(cgroup_tg(cgrp));
> +}
> +
> +static int cpu_cfs_period_write_u64(struct cgroup *cgrp, struct cftype *cftype,
> + u64 cfs_period_us)
> +{
> + return tg_set_cfs_period(cgroup_tg(cgrp), cfs_period_us);
> +}
> +
> +#endif /* CONFIG_CFS_BANDWIDTH */
> #endif /* CONFIG_FAIR_GROUP_SCHED */
>
> #ifdef CONFIG_RT_GROUP_SCHED
> @@ -8857,6 +9034,18 @@ static struct cftype cpu_files[] = {
> .write_u64 = cpu_shares_write_u64,
> },
> #endif
> +#ifdef CONFIG_CFS_BANDWIDTH
> + {
> + .name = "cfs_quota_us",
> + .read_s64 = cpu_cfs_quota_read_s64,
> + .write_s64 = cpu_cfs_quota_write_s64,
> + },
> + {
> + .name = "cfs_period_us",
> + .read_u64 = cpu_cfs_period_read_u64,
> + .write_u64 = cpu_cfs_period_write_u64,
> + },
> +#endif
> #ifdef CONFIG_RT_GROUP_SCHED
> {
> .name = "rt_runtime_us",
> @@ -9166,4 +9355,3 @@ struct cgroup_subsys cpuacct_subsys = {
> .subsys_id = cpuacct_subsys_id,
> };
> #endif /* CONFIG_CGROUP_CPUACCT */
> -
> Index: tip/kernel/sched_fair.c
> ===================================================================
> --- tip.orig/kernel/sched_fair.c
> +++ tip/kernel/sched_fair.c
> @@ -1256,6 +1256,22 @@ entity_tick(struct cfs_rq *cfs_rq, struc
> check_preempt_tick(cfs_rq, curr);
> }
>
> +
> +/**************************************************
> + * CFS bandwidth control machinery
> + */
> +
> +#ifdef CONFIG_CFS_BANDWIDTH
> +/*
> + * default period for cfs group bandwidth.
> + * default: 0.1s, units: nanoseconds
> + */
> +static inline u64 default_cfs_period(void)
> +{
> + return 100000000ULL;
> +}
> +#endif
> +
> /**************************************************
> * CFS operations on tasks:
> */
>
>