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Subject[CFS Bandwidth Control v4 1/7] sched: introduce primitives to account for CFS bandwidth tracking
In this patch we introduce the notion of CFS bandwidth, to account for the
realities of SMP this is 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_rq's can allocate from. It uses the new cfs_bandwidth
structure.
- The local bandwidth is tracked per-cfs_rq, this represents allotments from
the global pool
bandwidth assigned to a task_group, this is tracked using the
new cfs_bandwidth structure.

Bandwidth is managed via cgroupfs via two new files in 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.

A per-cfs_bandwidth timer is also introduced to handle future refresh at
period expiration. There's some minor refactoring here so that
start_bandwidth_timer() functionality can be shared

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>
---
init/Kconfig | 9 +
kernel/sched.c | 264 +++++++++++++++++++++++++++++++++++++++++++++++-----
kernel/sched_fair.c | 19 +++
3 files changed, 269 insertions(+), 23 deletions(-)

Index: tip/init/Kconfig
===================================================================
--- tip.orig/init/Kconfig
+++ tip/init/Kconfig
@@ -698,6 +698,15 @@ 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 quota and period for cpu
+ bandwidth provisioning on a per-cgroup basis.
+
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
@@ -194,10 +194,28 @@ static inline int rt_bandwidth_enabled(v
return sysctl_sched_rt_runtime >= 0;
}

-static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
+static void start_bandwidth_timer(struct hrtimer *period_timer, ktime_t period)
{
- ktime_t now;
+ unsigned long delta;
+ ktime_t soft, hard, now;
+
+ for (;;) {
+ if (hrtimer_active(period_timer))
+ break;

+ now = hrtimer_cb_get_time(period_timer);
+ hrtimer_forward(period_timer, now, period);
+
+ soft = hrtimer_get_softexpires(period_timer);
+ hard = hrtimer_get_expires(period_timer);
+ delta = ktime_to_ns(ktime_sub(hard, soft));
+ __hrtimer_start_range_ns(period_timer, soft, delta,
+ HRTIMER_MODE_ABS_PINNED, 0);
+ }
+}
+
+static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
+{
if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
return;

@@ -205,22 +223,7 @@ static void start_rt_bandwidth(struct rt
return;

raw_spin_lock(&rt_b->rt_runtime_lock);
- for (;;) {
- unsigned long delta;
- ktime_t soft, hard;
-
- if (hrtimer_active(&rt_b->rt_period_timer))
- break;
-
- now = hrtimer_cb_get_time(&rt_b->rt_period_timer);
- hrtimer_forward(&rt_b->rt_period_timer, now, rt_b->rt_period);
-
- soft = hrtimer_get_softexpires(&rt_b->rt_period_timer);
- hard = hrtimer_get_expires(&rt_b->rt_period_timer);
- delta = ktime_to_ns(ktime_sub(hard, soft));
- __hrtimer_start_range_ns(&rt_b->rt_period_timer, soft, delta,
- HRTIMER_MODE_ABS_PINNED, 0);
- }
+ start_bandwidth_timer(&rt_b->rt_period_timer, rt_b->rt_period);
raw_spin_unlock(&rt_b->rt_runtime_lock);
}

@@ -245,6 +248,15 @@ struct cfs_rq;

static LIST_HEAD(task_groups);

+#ifdef CONFIG_CFS_BANDWIDTH
+struct cfs_bandwidth {
+ raw_spinlock_t lock;
+ ktime_t period;
+ u64 runtime, quota;
+ struct hrtimer period_timer;
+};
+#endif
+
/* task group related information */
struct task_group {
struct cgroup_subsys_state css;
@@ -276,6 +288,10 @@ struct task_group {
#ifdef CONFIG_SCHED_AUTOGROUP
struct autogroup *autogroup;
#endif
+
+#ifdef CONFIG_CFS_BANDWIDTH
+ struct cfs_bandwidth cfs_bandwidth;
+#endif
};

/* task_group_lock serializes the addition/removal of task groups */
@@ -370,9 +386,76 @@ struct cfs_rq {

unsigned long load_contribution;
#endif
+#ifdef CONFIG_CFS_BANDWIDTH
+ u64 quota_assigned, quota_used;
+#endif
#endif
};

+#ifdef CONFIG_CFS_BANDWIDTH
+static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun);
+
+static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
+{
+ struct cfs_bandwidth *cfs_b =
+ container_of(timer, struct cfs_bandwidth, period_timer);
+ ktime_t now;
+ int overrun;
+ int idle = 0;
+
+ for (;;) {
+ now = hrtimer_cb_get_time(timer);
+ overrun = hrtimer_forward(timer, now, cfs_b->period);
+
+ if (!overrun)
+ break;
+
+ idle = do_sched_cfs_period_timer(cfs_b, overrun);
+ }
+
+ return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
+}
+
+static
+void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, u64 quota, u64 period)
+{
+ raw_spin_lock_init(&cfs_b->lock);
+ cfs_b->quota = cfs_b->runtime = quota;
+ cfs_b->period = ns_to_ktime(period);
+
+ hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ cfs_b->period_timer.function = sched_cfs_period_timer;
+}
+
+static
+void init_cfs_rq_quota(struct cfs_rq *cfs_rq)
+{
+ cfs_rq->quota_used = 0;
+ if (cfs_rq->tg->cfs_bandwidth.quota == RUNTIME_INF)
+ cfs_rq->quota_assigned = RUNTIME_INF;
+ else
+ cfs_rq->quota_assigned = 0;
+}
+
+static void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
+{
+ if (cfs_b->quota == RUNTIME_INF)
+ return;
+
+ if (hrtimer_active(&cfs_b->period_timer))
+ return;
+
+ raw_spin_lock(&cfs_b->lock);
+ start_bandwidth_timer(&cfs_b->period_timer, cfs_b->period);
+ raw_spin_unlock(&cfs_b->lock);
+}
+
+static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
+{
+ hrtimer_cancel(&cfs_b->period_timer);
+}
+#endif
+
/* Real-Time classes' related field in a runqueue: */
struct rt_rq {
struct rt_prio_array active;
@@ -8038,6 +8121,9 @@ static void init_tg_cfs_entry(struct tas
tg->cfs_rq[cpu] = cfs_rq;
init_cfs_rq(cfs_rq, rq);
cfs_rq->tg = tg;
+#ifdef CONFIG_CFS_BANDWIDTH
+ init_cfs_rq_quota(cfs_rq);
+#endif

tg->se[cpu] = se;
/* se could be NULL for root_task_group */
@@ -8173,6 +8259,10 @@ 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).
*/
+#ifdef CONFIG_CFS_BANDWIDTH
+ init_cfs_bandwidth(&root_task_group.cfs_bandwidth,
+ RUNTIME_INF, sched_cfs_bandwidth_period);
+#endif
init_tg_cfs_entry(&root_task_group, &rq->cfs, NULL, i, NULL);
#endif /* CONFIG_FAIR_GROUP_SCHED */

@@ -8415,6 +8505,10 @@ static void free_fair_sched_group(struct
{
int i;

+#ifdef CONFIG_CFS_BANDWIDTH
+ destroy_cfs_bandwidth(&tg->cfs_bandwidth);
+#endif
+
for_each_possible_cpu(i) {
if (tg->cfs_rq)
kfree(tg->cfs_rq[i]);
@@ -8442,7 +8536,10 @@ int alloc_fair_sched_group(struct task_g
goto err;

tg->shares = NICE_0_LOAD;
-
+#ifdef CONFIG_CFS_BANDWIDTH
+ init_cfs_bandwidth(&tg->cfs_bandwidth, RUNTIME_INF,
+ sched_cfs_bandwidth_period);
+#endif
for_each_possible_cpu(i) {
rq = cpu_rq(i);

@@ -8822,7 +8919,7 @@ 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;
@@ -8861,7 +8958,7 @@ 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)
@@ -8886,7 +8983,7 @@ 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)
@@ -9107,6 +9204,116 @@ static u64 cpu_shares_read_u64(struct cg

return (u64) tg->shares;
}
+
+#ifdef CONFIG_CFS_BANDWIDTH
+static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
+{
+ int i;
+ static DEFINE_MUTEX(mutex);
+
+ if (tg == &root_task_group)
+ return -EINVAL;
+
+ if (!period)
+ return -EINVAL;
+
+ /*
+ * Ensure we have at least one tick 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 (NS_TO_JIFFIES(quota) < 1)
+ return -EINVAL;
+
+ mutex_lock(&mutex);
+ raw_spin_lock_irq(&tg->cfs_bandwidth.lock);
+ tg->cfs_bandwidth.period = ns_to_ktime(period);
+ tg->cfs_bandwidth.runtime = tg->cfs_bandwidth.quota = quota;
+ raw_spin_unlock_irq(&tg->cfs_bandwidth.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);
+ init_cfs_rq_quota(cfs_rq);
+ raw_spin_unlock_irq(&rq->lock);
+ }
+ mutex_unlock(&mutex);
+
+ return 0;
+}
+
+int tg_set_cfs_quota(struct task_group *tg, long cfs_runtime_us)
+{
+ u64 quota, period;
+
+ period = ktime_to_ns(tg->cfs_bandwidth.period);
+ if (cfs_runtime_us < 0)
+ quota = RUNTIME_INF;
+ else
+ quota = (u64)cfs_runtime_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.quota == RUNTIME_INF)
+ return -1;
+
+ quota_us = tg->cfs_bandwidth.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.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.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
@@ -9141,6 +9348,18 @@ 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",
@@ -9450,4 +9669,3 @@ 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
@@ -88,6 +88,15 @@ const_debug unsigned int sysctl_sched_mi
*/
unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;

+
+#ifdef CONFIG_CFS_BANDWIDTH
+/*
+ * default period for cfs group bandwidth.
+ * default: 0.5s, units: nanoseconds
+ */
+static u64 sched_cfs_bandwidth_period = 500000000ULL;
+#endif
+
static const struct sched_class fair_sched_class;

/**************************************************************
@@ -397,6 +406,9 @@ static void __enqueue_entity(struct cfs_

rb_link_node(&se->run_node, parent, link);
rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
+#ifdef CONFIG_CFS_BANDWIDTH
+ start_cfs_bandwidth(&cfs_rq->tg->cfs_bandwidth);
+#endif
}

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -1369,6 +1381,13 @@ static void dequeue_task_fair(struct rq
hrtick_update(rq);
}

+#ifdef CONFIG_CFS_BANDWIDTH
+static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
+{
+ return 1;
+}
+#endif
+
#ifdef CONFIG_SMP

static void task_waking_fair(struct rq *rq, struct task_struct *p)



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