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

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:
*/



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