linux-kernel - [patch 25/29] sched: Fix sched rt group scheduling when hierachy is enabled

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Date:	Thu, 10 Mar 2011 15:54:31 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: [patch 25/29] sched: Fix sched rt group scheduling when hierachy is enabled

2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Balbir Singh <balbir@...ux.vnet.ibm.com>

commit 0c3b9168017cbad2c4af3dd65ec93fe646eeaa62 upstream.

The current sched rt code is broken when it comes to hierarchical
scheduling, this patch fixes two problems

1. It adds redundant enqueuing (harmless) when it finds a queue
   has tasks enqueued, but it has no run time and it is not
   throttled.

2. The most important change is in sched_rt_rq_enqueue/dequeue.
   The code just picks the rt_rq belonging to the current cpu
   on which the period timer runs, the patch fixes it, so that
   the correct rt_se is enqueued/dequeued.

Tested with a simple hierarchy

/c/d, c and d assigned similar runtimes of 50,000 and a while
1 loop runs within "d". Both c and d get throttled, without
the patch, the task just stops running and never runs (depends
on where the sched_rt b/w timer runs). With the patch, the
task is throttled and runs as expected.

[ bharata, suggestions on how to pick the rt_se belong to the
  rt_rq and correct cpu ]

Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <20110303113435.GA2868@...bir.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/sched_rt.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -199,11 +199,12 @@ static void dequeue_rt_entity(struct sch
 
 static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
 {
-	int this_cpu = smp_processor_id();
 	struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
 	struct sched_rt_entity *rt_se;
 
-	rt_se = rt_rq->tg->rt_se[this_cpu];
+	int cpu = cpu_of(rq_of_rt_rq(rt_rq));
+
+	rt_se = rt_rq->tg->rt_se[cpu];
 
 	if (rt_rq->rt_nr_running) {
 		if (rt_se && !on_rt_rq(rt_se))
@@ -215,10 +216,10 @@ static void sched_rt_rq_enqueue(struct r
 
 static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
 {
-	int this_cpu = smp_processor_id();
 	struct sched_rt_entity *rt_se;
+	int cpu = cpu_of(rq_of_rt_rq(rt_rq));
 
-	rt_se = rt_rq->tg->rt_se[this_cpu];
+	rt_se = rt_rq->tg->rt_se[cpu];
 
 	if (rt_se && on_rt_rq(rt_se))
 		dequeue_rt_entity(rt_se);
@@ -546,8 +547,11 @@ static int do_sched_rt_period_timer(stru
 			if (rt_rq->rt_time || rt_rq->rt_nr_running)
 				idle = 0;
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
-		} else if (rt_rq->rt_nr_running)
+		} else if (rt_rq->rt_nr_running) {
 			idle = 0;
+			if (!rt_rq_throttled(rt_rq))
+				enqueue = 1;
+		}
 
 		if (enqueue)
 			sched_rt_rq_enqueue(rt_rq);


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