sched: Add support for unthrottling group entities

At the start of each period we refresh the global bandwidth pool.  At this time
we must also unthrottle any cfs_rq entities who are now within bandwidth once
more (as quota permits).

Unthrottled entities have their corresponding cfs_rq->throttled flag cleared
and their entities re-enqueued.

Signed-off-by: Paul Turner <pjt@google.com>
Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110721184757.574628950@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 123 insertions, 4 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 72c9d4ed5991..76411950ff3b 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1439,6 +1439,84 @@ static __used void throttle_cfs_rq(struct cfs_rq *cfs_rq)
         raw_spin_unlock(&cfs_b->lock);
 }
 
+static void unthrottle_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;
+        int enqueue = 1;
+        long task_delta;
+
+        se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
+
+        cfs_rq->throttled = 0;
+        raw_spin_lock(&cfs_b->lock);
+        list_del_rcu(&cfs_rq->throttled_list);
+        raw_spin_unlock(&cfs_b->lock);
+
+        if (!cfs_rq->load.weight)
+                return;
+
+        task_delta = cfs_rq->h_nr_running;
+        for_each_sched_entity(se) {
+                if (se->on_rq)
+                        enqueue = 0;
+
+                cfs_rq = cfs_rq_of(se);
+                if (enqueue)
+                        enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
+                cfs_rq->h_nr_running += task_delta;
+
+                if (cfs_rq_throttled(cfs_rq))
+                        break;
+        }
+
+        if (!se)
+                rq->nr_running += task_delta;
+
+        /* determine whether we need to wake up potentially idle cpu */
+        if (rq->curr == rq->idle && rq->cfs.nr_running)
+                resched_task(rq->curr);
+}
+
+static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
+                u64 remaining, u64 expires)
+{
+        struct cfs_rq *cfs_rq;
+        u64 runtime = remaining;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
+                                throttled_list) {
+                struct rq *rq = rq_of(cfs_rq);
+
+                raw_spin_lock(&rq->lock);
+                if (!cfs_rq_throttled(cfs_rq))
+                        goto next;
+
+                runtime = -cfs_rq->runtime_remaining + 1;
+                if (runtime > remaining)
+                        runtime = remaining;
+                remaining -= runtime;
+
+                cfs_rq->runtime_remaining += runtime;
+                cfs_rq->runtime_expires = expires;
+
+                /* we check whether we're throttled above */
+                if (cfs_rq->runtime_remaining > 0)
+                        unthrottle_cfs_rq(cfs_rq);
+
+next:
+                raw_spin_unlock(&rq->lock);
+
+                if (!remaining)
+                        break;
+        }
+        rcu_read_unlock();
+
+        return remaining;
+}
+
 /*
  * Responsible for refilling a task_group's bandwidth and unthrottling its
  * cfs_rqs as appropriate. If there has been no activity within the last
@@ -1447,23 +1525,64 @@ static __used void throttle_cfs_rq(struct cfs_rq *cfs_rq)
  */
 static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
 {
-        int idle = 1;
+        u64 runtime, runtime_expires;
+        int idle = 1, throttled;
 
         raw_spin_lock(&cfs_b->lock);
         /* no need to continue the timer with no bandwidth constraint */
         if (cfs_b->quota == RUNTIME_INF)
                 goto out_unlock;
 
-        idle = cfs_b->idle;
+        throttled = !list_empty(&cfs_b->throttled_cfs_rq);
+        /* idle depends on !throttled (for the case of a large deficit) */
+        idle = cfs_b->idle && !throttled;
+
         /* if we're going inactive then everything else can be deferred */
         if (idle)
                 goto out_unlock;
 
         __refill_cfs_bandwidth_runtime(cfs_b);
 
+        if (!throttled) {
+                /* mark as potentially idle for the upcoming period */
+                cfs_b->idle = 1;
+                goto out_unlock;
+        }
+
+        /*
+         * There are throttled entities so we must first use the new bandwidth
+         * to unthrottle them before making it generally available.  This
+         * ensures that all existing debts will be paid before a new cfs_rq is
+         * allowed to run.
+         */
+        runtime = cfs_b->runtime;
+        runtime_expires = cfs_b->runtime_expires;
+        cfs_b->runtime = 0;
+
+        /*
+         * This check is repeated as we are holding onto the new bandwidth
+         * while we unthrottle.  This can potentially race with an unthrottled
+         * group trying to acquire new bandwidth from the global pool.
+         */
+        while (throttled && runtime > 0) {
+                raw_spin_unlock(&cfs_b->lock);
+                /* we can't nest cfs_b->lock while distributing bandwidth */
+                runtime = distribute_cfs_runtime(cfs_b, runtime,
+                                                 runtime_expires);
+                raw_spin_lock(&cfs_b->lock);
+
+                throttled = !list_empty(&cfs_b->throttled_cfs_rq);
+        }
 
-        /* mark as potentially idle for the upcoming period */
-        cfs_b->idle = 1;
+        /* return (any) remaining runtime */
+        cfs_b->runtime = runtime;
+        /*
+         * While we are ensured activity in the period following an
+         * unthrottle, this also covers the case in which the new bandwidth is
+         * insufficient to cover the existing bandwidth deficit.  (Forcing the
+         * timer to remain active while there are any throttled entities.)
+         */
+        cfs_b->idle = 0;
 out_unlock:
         if (idle)
                 cfs_b->timer_active = 0;