sched: rt time limit

Very simple time limit on the realtime scheduling classes.
Allow the rq's realtime class to consume sched_rt_ratio of every
sched_rt_period slice. If the class exceeds this quota the fair class
will preempt the realtime class.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 53 insertions, 0 deletions

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 83fbbcb8019e..fd10d965aa06 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -45,6 +45,50 @@ static void update_rt_migration(struct rq *rq)
 }
 #endif /* CONFIG_SMP */
 
+static int sched_rt_ratio_exceeded(struct rq *rq, struct rt_rq *rt_rq)
+{
+        u64 period, ratio;
+
+        if (sysctl_sched_rt_ratio == SCHED_RT_FRAC)
+                return 0;
+
+        if (rt_rq->rt_throttled)
+                return 1;
+
+        period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
+        ratio = (period * sysctl_sched_rt_ratio) >> SCHED_RT_FRAC_SHIFT;
+
+        if (rt_rq->rt_time > ratio) {
+                rt_rq->rt_throttled = rq->clock + period - rt_rq->rt_time;
+                return 1;
+        }
+
+        return 0;
+}
+
+static void update_sched_rt_period(struct rq *rq)
+{
+        while (rq->clock > rq->rt_period_expire) {
+                u64 period, ratio;
+
+                period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
+                ratio = (period * sysctl_sched_rt_ratio) >> SCHED_RT_FRAC_SHIFT;
+
+                rq->rt.rt_time -= min(rq->rt.rt_time, ratio);
+                rq->rt_period_expire += period;
+        }
+
+        /*
+         * When the rt throttle is expired, let them rip.
+         * (XXX: use hrtick when available)
+         */
+        if (rq->rt.rt_throttled && rq->clock > rq->rt.rt_throttled) {
+                rq->rt.rt_throttled = 0;
+                if (!sched_rt_ratio_exceeded(rq, &rq->rt))
+                        resched_task(rq->curr);
+        }
+}
+
 /*
  * Update the current task's runtime statistics. Skip current tasks that
  * are not in our scheduling class.
@@ -66,6 +110,11 @@ static void update_curr_rt(struct rq *rq)
         curr->se.sum_exec_runtime += delta_exec;
         curr->se.exec_start = rq->clock;
         cpuacct_charge(curr, delta_exec);
+
+        rq->rt.rt_time += delta_exec;
+        update_sched_rt_period(rq);
+        if (sched_rt_ratio_exceeded(rq, &rq->rt))
+                resched_task(curr);
 }
 
 static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
@@ -208,8 +257,12 @@ static struct task_struct *pick_next_task_rt(struct rq *rq)
         struct rt_prio_array *array = &rq->rt.active;
         struct task_struct *next;
         struct list_head *queue;
+        struct rt_rq *rt_rq = &rq->rt;
         int idx;
 
+        if (sched_rt_ratio_exceeded(rq, rt_rq))
+                return NULL;
+
         idx = sched_find_first_bit(array->bitmap);
         if (idx >= MAX_RT_PRIO)
                 return NULL;