sched: Implement head queueing for sched_rt

The ability of enqueueing a task to the head of a SCHED_FIFO priority
list is required to fix some violations of POSIX scheduling policy.

Implement the functionality in sched_rt.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Tested-by: Carsten Emde <cbe@osadl.org>
Tested-by: Mathias Weber <mathias.weber.mw1@roche.com>
LKML-Reference: <20100120171629.772169931@linutronix.de>

1 files changed, 11 insertions, 8 deletions

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 38076dabb44a..ca49ceb01201 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -194,7 +194,7 @@ static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
         return rt_se->my_q;
 }
 
-static void enqueue_rt_entity(struct sched_rt_entity *rt_se);
+static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head);
 static void dequeue_rt_entity(struct sched_rt_entity *rt_se);
 
 static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
@@ -204,7 +204,7 @@ static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
 
         if (rt_rq->rt_nr_running) {
                 if (rt_se && !on_rt_rq(rt_se))
-                        enqueue_rt_entity(rt_se);
+                        enqueue_rt_entity(rt_se, false);
                 if (rt_rq->highest_prio.curr < curr->prio)
                         resched_task(curr);
         }
@@ -803,7 +803,7 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
         dec_rt_group(rt_se, rt_rq);
 }
 
-static void __enqueue_rt_entity(struct sched_rt_entity *rt_se)
+static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
 {
         struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
         struct rt_prio_array *array = &rt_rq->active;
@@ -819,7 +819,10 @@ static void __enqueue_rt_entity(struct sched_rt_entity *rt_se)
         if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
                 return;
 
-        list_add_tail(&rt_se->run_list, queue);
+        if (head)
+                list_add(&rt_se->run_list, queue);
+        else
+                list_add_tail(&rt_se->run_list, queue);
         __set_bit(rt_se_prio(rt_se), array->bitmap);
 
         inc_rt_tasks(rt_se, rt_rq);
@@ -856,11 +859,11 @@ static void dequeue_rt_stack(struct sched_rt_entity *rt_se)
         }
 }
 
-static void enqueue_rt_entity(struct sched_rt_entity *rt_se)
+static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
 {
         dequeue_rt_stack(rt_se);
         for_each_sched_rt_entity(rt_se)
-                __enqueue_rt_entity(rt_se);
+                __enqueue_rt_entity(rt_se, head);
 }
 
 static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
@@ -871,7 +874,7 @@ static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
                 struct rt_rq *rt_rq = group_rt_rq(rt_se);
 
                 if (rt_rq && rt_rq->rt_nr_running)
-                        __enqueue_rt_entity(rt_se);
+                        __enqueue_rt_entity(rt_se, false);
         }
 }
 
@@ -886,7 +889,7 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup, bool head)
         if (wakeup)
                 rt_se->timeout = 0;
 
-        enqueue_rt_entity(rt_se);
+        enqueue_rt_entity(rt_se, head);
 
         if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
                 enqueue_pushable_task(rq, p);