This is an implementation of Steve's idea where we should update the RQ
concept of priority to show the highest-task, even if that task is not (yet)
running. This prevents us from pushing multiple tasks to the RQ before it
gets a chance to reschedule.
Signed-off-by: Gregory Haskins <[email protected]>
---
kernel/sched.c | 43 ++++++++++++++++++++++++++++++++++---------
1 files changed, 34 insertions(+), 9 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index ce5292f..9e5cc2c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -304,7 +304,7 @@ struct rq {
#ifdef CONFIG_PREEMPT_RT
unsigned long rt_nr_running;
unsigned long rt_nr_uninterruptible;
- int curr_prio;
+ int highest_prio;
#endif
unsigned long switch_timestamp;
@@ -368,11 +368,29 @@ static DEFINE_MUTEX(sched_hotcpu_mutex);
#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
static inline void set_rq_prio(struct rq *rq, int prio)
{
- rq->curr_prio = prio;
+ rq->highest_prio = prio;
+}
+
+/*
+ * We dont care what the exact normal priority is. We only care about
+ * RT-priority, vs non-RT (normal or idle). So flatten the priority if its a
+ * non-RT variety. This will reduce cache-thrashing on the rq->highest_prio.
+ */
+static inline void update_rq_prio(struct rq *rq)
+{
+ struct rt_prio_array *array = &rq->rt.active;
+ int prio = sched_find_first_bit(array->bitmap);
+
+ if ((prio != MAX_PRIO) && (prio > MAX_RT_PRIO))
+ prio = MAX_RT_PRIO;
+
+ if (rq->highest_prio != prio)
+ set_rq_prio(rq, prio);
}
#else
#define set_rq_prio(rq, prio) do { } while(0)
+#define update_rq_prio(rq) do { } while(0)
#endif
static inline void check_preempt_curr(struct rq *rq, struct task_struct *p)
@@ -1023,12 +1041,14 @@ static void enqueue_task(struct rq *rq, struct task_struct *p, int wakeup)
sched_info_queued(p);
p->sched_class->enqueue_task(rq, p, wakeup);
p->se.on_rq = 1;
+ update_rq_prio(rq);
}
static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
{
p->sched_class->dequeue_task(rq, p, sleep);
p->se.on_rq = 0;
+ update_rq_prio(rq);
}
/*
@@ -1527,14 +1547,14 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task,
continue;
/* We look for lowest RT prio or non-rt CPU */
- if (rq->curr_prio >= MAX_RT_PRIO) {
+ if (rq->highest_prio >= MAX_RT_PRIO) {
lowest_rq = rq;
break;
}
/* no locking for now */
- if (rq->curr_prio > task->prio &&
- (!lowest_rq || rq->curr_prio < lowest_rq->curr_prio)) {
+ if (rq->highest_prio > task->prio &&
+ (!lowest_rq || rq->highest_prio < lowest_rq->highest_prio)) {
lowest_rq = rq;
}
}
@@ -1560,7 +1580,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task,
}
/* If this rq is still suitable use it. */
- if (lowest_rq->curr_prio > task->prio)
+ if (lowest_rq->highest_prio > task->prio)
break;
/* try again */
@@ -2336,10 +2356,8 @@ static inline void finish_task_switch(struct rq *rq, struct task_struct *prev)
*/
prev_state = prev->state;
_finish_arch_switch(prev);
-
- set_rq_prio(rq, current->prio);
-
finish_lock_switch(rq, prev);
+
#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
/*
* If we pushed an RT task off the runqueue,
@@ -4654,6 +4672,9 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
prev_resched = _need_resched();
if (on_rq) {
+ /*
+ * Note: RQ priority gets updated in the enqueue/dequeue logic
+ */
enqueue_task(rq, p, 0);
/*
* Reschedule if we are currently running on this runqueue and
@@ -4720,6 +4741,10 @@ void set_user_nice(struct task_struct *p, long nice)
*/
if (delta < 0 || (delta > 0 && task_running(rq, p)))
resched_task(rq->curr);
+
+ /*
+ * Note: RQ priority gets updated in the enqueue/dequeue logic
+ */
}
out_unlock:
task_rq_unlock(rq, &flags);
-
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