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>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110721184757.480608533@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 85 insertions, 4 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 9d1adbd0b615..72c9d4ed5991 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1291,7 +1291,8 @@ static void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
         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);
@@ -1332,6 +1333,8 @@ static void assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
          */
         if ((s64)(expires - cfs_rq->runtime_expires) > 0)
                 cfs_rq->runtime_expires = expires;
+
+        return cfs_rq->runtime_remaining > 0;
 }
 
 /*
@@ -1378,7 +1381,12 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
         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,
@@ -1390,6 +1398,47 @@ static __always_inline void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
         __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
@@ -1425,6 +1474,11 @@ 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
 
 /**************************************************
@@ -1503,7 +1557,17 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
                         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;
         }
 
@@ -1511,11 +1575,15 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
                 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);
 }
 
@@ -1535,6 +1603,15 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
         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 */
@@ -1557,11 +1634,15 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
                 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);
 }