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Subject[patch 08/18] sched: add support for throttling group entities
Now that consumption is tracked (via update_curr()) we add support to throttle
group entities (and their corresponding cfs_rqs) in the case where this is no
run-time remaining.

Throttled entities are dequeued to prevent scheduling, additionally we mark
them as throttled (using cfs_rq->throttled) to prevent them from becoming
re-enqueued until they are unthrottled. A list of a task_group's throttled
entities are maintained on the cfs_bandwidth structure.

Note: While the machinery for throttling is added in this patch the act of
throttling an entity exceeding its bandwidth is deferred until later within
the series.

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

---
kernel/sched.c | 7 ++++
kernel/sched_fair.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 92 insertions(+), 4 deletions(-)

Index: tip/kernel/sched_fair.c
===================================================================
--- tip.orig/kernel/sched_fair.c
+++ tip/kernel/sched_fair.c
@@ -1313,7 +1313,8 @@ static void __refill_cfs_bandwidth_runti
cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
}

-static void assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
+/* returns 0 on failure to allocate runtime */
+static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
struct task_group *tg = cfs_rq->tg;
struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
@@ -1354,6 +1355,8 @@ static void assign_cfs_rq_runtime(struct
*/
if ((s64)(expires - cfs_rq->runtime_expires) > 0)
cfs_rq->runtime_expires = expires;
+
+ return cfs_rq->runtime_remaining > 0;
}

/*
@@ -1400,7 +1403,12 @@ static void __account_cfs_rq_runtime(str
if (likely(cfs_rq->runtime_remaining > 0))
return;

- assign_cfs_rq_runtime(cfs_rq);
+ /*
+ * if we're unable to extend our runtime we resched so that the active
+ * hierarchy can be throttled
+ */
+ if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
+ resched_task(rq_of(cfs_rq)->curr);
}

static __always_inline void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
@@ -1412,6 +1420,47 @@ static __always_inline void account_cfs_
__account_cfs_rq_runtime(cfs_rq, delta_exec);
}

+static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
+{
+ return cfs_rq->throttled;
+}
+
+static __used void throttle_cfs_rq(struct cfs_rq *cfs_rq)
+{
+ struct rq *rq = rq_of(cfs_rq);
+ struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
+ struct sched_entity *se;
+ long task_delta, dequeue = 1;
+
+ se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
+
+ /* account load preceding throttle */
+ update_cfs_load(cfs_rq, 0);
+
+ task_delta = cfs_rq->h_nr_running;
+ for_each_sched_entity(se) {
+ struct cfs_rq *qcfs_rq = cfs_rq_of(se);
+ /* throttled entity or throttle-on-deactivate */
+ if (!se->on_rq)
+ break;
+
+ if (dequeue)
+ dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
+ qcfs_rq->h_nr_running -= task_delta;
+
+ if (qcfs_rq->load.weight)
+ dequeue = 0;
+ }
+
+ if (!se)
+ rq->nr_running -= task_delta;
+
+ cfs_rq->throttled = 1;
+ raw_spin_lock(&cfs_b->lock);
+ list_add_tail_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
+ raw_spin_unlock(&cfs_b->lock);
+}
+
/*
* Responsible for refilling a task_group's bandwidth and unthrottling its
* cfs_rqs as appropriate. If there has been no activity within the last
@@ -1447,6 +1496,11 @@ out_unlock:
#else
static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
unsigned long delta_exec) {}
+
+static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
+{
+ return 0;
+}
#endif

/**************************************************
@@ -1525,7 +1579,17 @@ enqueue_task_fair(struct rq *rq, struct
break;
cfs_rq = cfs_rq_of(se);
enqueue_entity(cfs_rq, se, flags);
+
+ /*
+ * end evaluation on encountering a throttled cfs_rq
+ *
+ * note: in the case of encountering a throttled cfs_rq we will
+ * post the final h_nr_running increment below.
+ */
+ if (cfs_rq_throttled(cfs_rq))
+ break;
cfs_rq->h_nr_running++;
+
flags = ENQUEUE_WAKEUP;
}

@@ -1533,11 +1597,15 @@ enqueue_task_fair(struct rq *rq, struct
cfs_rq = cfs_rq_of(se);
cfs_rq->h_nr_running++;

+ if (cfs_rq_throttled(cfs_rq))
+ break;
+
update_cfs_load(cfs_rq, 0);
update_cfs_shares(cfs_rq);
}

- inc_nr_running(rq);
+ if (!se)
+ inc_nr_running(rq);
hrtick_update(rq);
}

@@ -1557,6 +1625,15 @@ static void dequeue_task_fair(struct rq
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
dequeue_entity(cfs_rq, se, flags);
+
+ /*
+ * end evaluation on encountering a throttled cfs_rq
+ *
+ * note: in the case of encountering a throttled cfs_rq we will
+ * post the final h_nr_running decrement below.
+ */
+ if (cfs_rq_throttled(cfs_rq))
+ break;
cfs_rq->h_nr_running--;

/* Don't dequeue parent if it has other entities besides us */
@@ -1579,11 +1656,15 @@ static void dequeue_task_fair(struct rq
cfs_rq = cfs_rq_of(se);
cfs_rq->h_nr_running--;

+ if (cfs_rq_throttled(cfs_rq))
+ break;
+
update_cfs_load(cfs_rq, 0);
update_cfs_shares(cfs_rq);
}

- dec_nr_running(rq);
+ if (!se)
+ dec_nr_running(rq);
hrtick_update(rq);
}

Index: tip/kernel/sched.c
===================================================================
--- tip.orig/kernel/sched.c
+++ tip/kernel/sched.c
@@ -257,6 +257,8 @@ struct cfs_bandwidth {

int idle, timer_active;
struct hrtimer period_timer;
+ struct list_head throttled_cfs_rq;
+
#endif
};

@@ -396,6 +398,9 @@ struct cfs_rq {
int runtime_enabled;
u64 runtime_expires;
s64 runtime_remaining;
+
+ int throttled;
+ struct list_head throttled_list;
#endif
#endif
};
@@ -438,6 +443,7 @@ static void init_cfs_bandwidth(struct cf
cfs_b->quota = RUNTIME_INF;
cfs_b->period = ns_to_ktime(default_cfs_period());

+ INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
cfs_b->period_timer.function = sched_cfs_period_timer;
}
@@ -445,6 +451,7 @@ static void init_cfs_bandwidth(struct cf
static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
cfs_rq->runtime_enabled = 0;
+ INIT_LIST_HEAD(&cfs_rq->throttled_list);
}

/* requires cfs_b->lock, may release to reprogram timer */



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