[tip:sched/core] sched: Add support for unthrottling group entities

tip-bot for Paul Turner
2011-08-14T16:28:07Z

Commit-ID: 671fd9dabe5239ad218c7eb48b2b9edee50250e6
Gitweb: http://git.kernel.org/tip/671fd9dabe5239ad218c7eb48b2b9edee50250e6
Author: Paul Turner <pjt@google.com>
AuthorDate: Thu, 21 Jul 2011 09:43:34 -0700
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Sun, 14 Aug 2011 12:03:36 +0200

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>
---
kernel/sched.c | 3 +
kernel/sched_fair.c | 127 +++++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 126 insertions(+), 4 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 044260a..4bbabc2 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9192,6 +9192,9 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
raw_spin_lock_irq(&rq->lock);
cfs_rq->runtime_enabled = runtime_enabled;
cfs_rq->runtime_remaining = 0;
+
+ if (cfs_rq_throttled(cfs_rq))
+ unthrottle_cfs_rq(cfs_rq);
raw_spin_unlock_irq(&rq->lock);
}
out_unlock:
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 72c9d4e..7641195 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;