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Subject[patch 04/17] sched: validate CFS quota hierarchies
Add constraints validation for CFS bandwidth hierarchies.

Validate that:
max(child bandwidth) <= parent_bandwidth

In a quota limited hierarchy, an unconstrained entity
(e.g. bandwidth==RUNTIME_INF) inherits the bandwidth of its parent.

This constraint is chosen over sum(child_bandwidth) as notion of over-commit is
valuable within SCHED_OTHER. Some basic code from the RT case is re-factored
for reuse.

Signed-off-by: Paul Turner <pjt@google.com>

---
kernel/sched.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 96 insertions(+), 13 deletions(-)
Index: tip/kernel/sched.c
===================================================================
--- tip.orig/kernel/sched.c
+++ tip/kernel/sched.c
@@ -249,6 +249,7 @@ struct cfs_bandwidth {
raw_spinlock_t lock;
ktime_t period;
u64 quota;
+ s64 hierarchal_quota;
#endif
};

@@ -8522,12 +8523,7 @@ unsigned long sched_group_shares(struct
}
#endif

-#ifdef CONFIG_RT_GROUP_SCHED
-/*
- * Ensure that the real time constraints are schedulable.
- */
-static DEFINE_MUTEX(rt_constraints_mutex);
-
+#if defined(CONFIG_RT_GROUP_SCHED) || defined(CONFIG_CFS_BANDWIDTH)
static unsigned long to_ratio(u64 period, u64 runtime)
{
if (runtime == RUNTIME_INF)
@@ -8535,6 +8531,13 @@ static unsigned long to_ratio(u64 period

return div64_u64(runtime << 20, period);
}
+#endif
+
+#ifdef CONFIG_RT_GROUP_SCHED
+/*
+ * Ensure that the real time constraints are schedulable.
+ */
+static DEFINE_MUTEX(rt_constraints_mutex);

/* Must be called with tasklist_lock held */
static inline int tg_has_rt_tasks(struct task_group *tg)
@@ -8555,7 +8558,7 @@ struct rt_schedulable_data {
u64 rt_runtime;
};

-static int tg_schedulable(struct task_group *tg, void *data)
+static int tg_rt_schedulable(struct task_group *tg, void *data)
{
struct rt_schedulable_data *d = data;
struct task_group *child;
@@ -8619,7 +8622,7 @@ static int __rt_schedulable(struct task_
.rt_runtime = runtime,
};

- return walk_tg_tree(tg_schedulable, tg_nop, &data);
+ return walk_tg_tree(tg_rt_schedulable, tg_nop, &data);
}

static int tg_set_rt_bandwidth(struct task_group *tg,
@@ -8878,14 +8881,17 @@ static u64 cpu_shares_read_u64(struct cg
}

#ifdef CONFIG_CFS_BANDWIDTH
+static DEFINE_MUTEX(cfs_constraints_mutex);
+
const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */
const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */

+static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);
+
static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
{
- int i;
+ int i, ret = 0;
struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
- static DEFINE_MUTEX(mutex);

if (tg == &root_task_group)
return -EINVAL;
@@ -8906,7 +8912,11 @@ static int tg_set_cfs_bandwidth(struct t
if (period > max_cfs_quota_period)
return -EINVAL;

- mutex_lock(&mutex);
+ mutex_lock(&cfs_constraints_mutex);
+ ret = __cfs_schedulable(tg, period, quota);
+ if (ret)
+ goto out_unlock;
+
raw_spin_lock_irq(&cfs_b->lock);
cfs_b->period = ns_to_ktime(period);
cfs_b->quota = quota;
@@ -8921,9 +8931,10 @@ static int tg_set_cfs_bandwidth(struct t
cfs_rq->runtime_remaining = 0;
raw_spin_unlock_irq(&rq->lock);
}
- mutex_unlock(&mutex);
+out_unlock:
+ mutex_unlock(&cfs_constraints_mutex);

- return 0;
+ return ret;
}

int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)
@@ -8997,6 +9008,78 @@ static int cpu_cfs_period_write_u64(stru
return tg_set_cfs_period(cgroup_tg(cgrp), cfs_period_us);
}

+struct cfs_schedulable_data {
+ struct task_group *tg;
+ u64 period, quota;
+};
+
+/*
+ * normalize group quota/period to be quota/max_period
+ * note: units are usecs
+ */
+static u64 normalize_cfs_quota(struct task_group *tg,
+ struct cfs_schedulable_data *d)
+{
+ u64 quota, period;
+
+ if (tg == d->tg) {
+ period = d->period;
+ quota = d->quota;
+ } else {
+ period = tg_get_cfs_period(tg);
+ quota = tg_get_cfs_quota(tg);
+ }
+
+ /* note: these should typically be equivalent */
+ if (quota == RUNTIME_INF || quota == -1)
+ return RUNTIME_INF;
+
+ return to_ratio(period, quota);
+}
+
+static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
+{
+ struct cfs_schedulable_data *d = data;
+ struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
+ s64 quota = 0, parent_quota = -1;
+
+ if (!tg->parent) {
+ quota = RUNTIME_INF;
+ } else {
+ struct cfs_bandwidth *parent_b = tg_cfs_bandwidth(tg->parent);
+
+ quota = normalize_cfs_quota(tg, d);
+ parent_quota = parent_b->hierarchal_quota;
+
+ /*
+ * ensure max(child_quota) <= parent_quota, inherit when no
+ * limit is set
+ */
+ if (quota == RUNTIME_INF)
+ quota = parent_quota;
+ else if (parent_quota != RUNTIME_INF && quota > parent_quota)
+ return -EINVAL;
+ }
+ cfs_b->hierarchal_quota = quota;
+
+ return 0;
+}
+
+static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
+{
+ struct cfs_schedulable_data data = {
+ .tg = tg,
+ .period = period,
+ .quota = quota,
+ };
+
+ if (quota != RUNTIME_INF) {
+ do_div(data.period, NSEC_PER_USEC);
+ do_div(data.quota, NSEC_PER_USEC);
+ }
+
+ return walk_tg_tree(tg_cfs_schedulable_down, tg_nop, &data);
+}
#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_FAIR_GROUP_SCHED */




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