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Subject[090/123] sched: Implement head queueing for sched_rt
From: Thomas Gleixner <tglx@linutronix.de>

commit 37dad3fce97f01e5149d69de0833d8452c0e862e upstream

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>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
kernel/sched_rt.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -194,7 +194,7 @@ static inline struct rt_rq *group_rt_rq(
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 r

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
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 s
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 sche
}
}

-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 sch
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 ta
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);



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