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Subject[RFC PATCH v1 1/4] sched: introduce primitives to account for CFS bandwidth tracking
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From: Paul Turner <pjt@google.com>

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>
---
init/Kconfig | 9 ++
kernel/sched.c | 275 +++++++++++++++++++++++++++++++++++++++++++++++----
kernel/sched_fair.c | 14 ++-
3 files changed, 273 insertions(+), 25 deletions(-)
diff --git a/init/Kconfig b/init/Kconfig
index d95ca7c..fb8c7d8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -496,6 +496,15 @@ config CGROUP_SCHED

endchoice

+config CFS_BANDWIDTH
+ bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
+ depends on EXPERIMENTAL
+ depends on FAIR_GROUP_SCHED && CGROUP_SCHED
+ default n
+ help
+ This option allows users to define quota and period for cpu
+ bandwidth provisioning on a per-cgroup basis.
+
menuconfig CGROUPS
boolean "Control Group support"
help
diff --git a/kernel/sched.c b/kernel/sched.c
index 3a8fb30..6cc4bf4 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -190,10 +190,28 @@ static inline int rt_bandwidth_enabled(void)
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;

@@ -201,22 +219,7 @@ static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
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);
}

@@ -241,6 +244,15 @@ 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 {
#ifdef CONFIG_CGROUP_SCHED
@@ -272,6 +284,10 @@ struct task_group {
struct task_group *parent;
struct list_head siblings;
struct list_head children;
+
+#ifdef CONFIG_CFS_BANDWIDTH
+ struct cfs_bandwidth cfs_bandwidth;
+#endif
};

#ifdef CONFIG_USER_SCHED
@@ -445,9 +461,76 @@ struct cfs_rq {
*/
unsigned long rq_weight;
#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;
@@ -1834,6 +1917,14 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
#endif
}

+#ifdef CONFIG_CFS_BANDWIDTH
+/*
+ * default period for cfs group bandwidth.
+ * default: 0.5s
+ */
+static u64 sched_cfs_bandwidth_period = 500000000ULL;
+#endif
+
#include "sched_stats.h"
#include "sched_idletask.c"
#include "sched_fair.c"
@@ -9422,6 +9513,9 @@ static void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
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
if (add)
list_add(&cfs_rq->leaf_cfs_rq_list, &rq->leaf_cfs_rq_list);

@@ -9594,6 +9688,10 @@ 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).
*/
+#ifdef CONFIG_CFS_BANDWIDTH
+ init_cfs_bandwidth(&init_task_group.cfs_bandwidth,
+ RUNTIME_INF, sched_cfs_bandwidth_period);
+#endif
init_tg_cfs_entry(&init_task_group, &rq->cfs, NULL, i, 1, NULL);
#elif defined CONFIG_USER_SCHED
root_task_group.shares = NICE_0_LOAD;
@@ -9851,6 +9949,10 @@ static void free_fair_sched_group(struct task_group *tg)
{
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]);
@@ -9878,7 +9980,10 @@ int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
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);

@@ -10333,7 +10438,7 @@ static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
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;
@@ -10372,7 +10477,7 @@ int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
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)
@@ -10397,7 +10502,7 @@ int sched_group_set_rt_period(struct task_group *tg, long rt_period_us)
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)
@@ -10604,6 +10709,120 @@ static u64 cpu_shares_read_u64(struct cgroup *cgrp, struct cftype *cft)

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 == &init_task_group)
+ return -EINVAL;
+
+ if (!period)
+ return -EINVAL;
+
+ mutex_lock(&mutex);
+ /*
+ * 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;
+
+ 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);
+ cfs_rq->quota_used = 0;
+ if (quota == RUNTIME_INF)
+ cfs_rq->quota_assigned = RUNTIME_INF;
+ else
+ cfs_rq->quota_assigned = 0;
+ 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
@@ -10638,6 +10857,18 @@ 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",
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 8fe7ee8..7b109ff 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -264,10 +264,8 @@ static inline void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
}
-
#endif /* CONFIG_FAIR_GROUP_SCHED */

-
/**************************************************************
* Scheduling class tree data structure manipulation methods:
*/
@@ -360,6 +358,9 @@ static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)

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)
@@ -1143,6 +1144,13 @@ static void yield_task_fair(struct rq *rq)
se->vruntime = rightmost->vruntime + 1;
}

+#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)
@@ -1172,7 +1180,7 @@ static void task_waking_fair(struct rq *rq, struct task_struct *p)
* We still saw a performance dip, some tracing learned us that between
* cgroup:/ and cgroup:/foo balancing the number of affine wakeups increased
* significantly. Therefore try to bias the error in direction of failing
- * the affine wakeup.
+ * the affie wakeup.
*
*/
static long effective_load(struct task_group *tg, int cpu,


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