sched: rt throttling vs no_hz

We need to teach no_hz about the rt throttling because its tick driven.

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

3 files changed, 43 insertions, 15 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 5ea2c533b432..22712b2e058a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -442,6 +442,7 @@ struct rq {
         struct cfs_rq cfs;
         struct rt_rq rt;
         u64 rt_period_expire;
+        int rt_throttled;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
         /* list of leaf cfs_rq on this cpu: */
@@ -594,6 +595,23 @@ static void update_rq_clock(struct rq *rq)
 #define task_rq(p)              cpu_rq(task_cpu(p))
 #define cpu_curr(cpu)           (cpu_rq(cpu)->curr)
 
+unsigned long rt_needs_cpu(int cpu)
+{
+        struct rq *rq = cpu_rq(cpu);
+        u64 delta;
+
+        if (!rq->rt_throttled)
+                return 0;
+
+        if (rq->clock > rq->rt_period_expire)
+                return 1;
+
+        delta = rq->rt_period_expire - rq->clock;
+        do_div(delta, NSEC_PER_SEC / HZ);
+
+        return (unsigned long)delta;
+}
+
 /*
  * Tunables that become constants when CONFIG_SCHED_DEBUG is off:
  */
@@ -7102,9 +7120,11 @@ static void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)
         /* delimiter for bitsearch: */
         __set_bit(MAX_RT_PRIO, array->bitmap);
 
+#if defined CONFIG_SMP || defined CONFIG_FAIR_GROUP_SCHED
+        rt_rq->highest_prio = MAX_RT_PRIO;
+#endif
 #ifdef CONFIG_SMP
         rt_rq->rt_nr_migratory = 0;
-        rt_rq->highest_prio = MAX_RT_PRIO;
         rt_rq->overloaded = 0;
 #endif
 
@@ -7191,6 +7211,7 @@ void __init sched_init(void)
                                 &per_cpu(init_sched_rt_entity, i), i, 1);
 #endif
                 rq->rt_period_expire = 0;
+                rq->rt_throttled = 0;
 
                 for (j = 0; j < CPU_LOAD_IDX_MAX; j++)
                         rq->cpu_load[j] = 0;
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 1144bf55669d..8bfdb3f8a52d 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -175,7 +175,11 @@ static int sched_rt_ratio_exceeded(struct rt_rq *rt_rq)
         ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
 
         if (rt_rq->rt_time > ratio) {
+                struct rq *rq = rq_of_rt_rq(rt_rq);
+
+                rq->rt_throttled = 1;
                 rt_rq->rt_throttled = 1;
+
                 sched_rt_ratio_dequeue(rt_rq);
                 return 1;
         }
@@ -183,18 +187,6 @@ static int sched_rt_ratio_exceeded(struct rt_rq *rt_rq)
         return 0;
 }
 
-static void __update_sched_rt_period(struct rt_rq *rt_rq, u64 period)
-{
-        unsigned long rt_ratio = sched_rt_ratio(rt_rq);
-        u64 ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
-
-        rt_rq->rt_time -= min(rt_rq->rt_time, ratio);
-        if (rt_rq->rt_throttled) {
-                rt_rq->rt_throttled = 0;
-                sched_rt_ratio_enqueue(rt_rq);
-        }
-}
-
 static void update_sched_rt_period(struct rq *rq)
 {
         struct rt_rq *rt_rq;
@@ -204,8 +196,18 @@ static void update_sched_rt_period(struct rq *rq)
                 period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
                 rq->rt_period_expire += period;
 
-                for_each_leaf_rt_rq(rt_rq, rq)
-                        __update_sched_rt_period(rt_rq, period);
+                for_each_leaf_rt_rq(rt_rq, rq) {
+                        unsigned long rt_ratio = sched_rt_ratio(rt_rq);
+                        u64 ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
+
+                        rt_rq->rt_time -= min(rt_rq->rt_time, ratio);
+                        if (rt_rq->rt_throttled) {
+                                rt_rq->rt_throttled = 0;
+                                sched_rt_ratio_enqueue(rt_rq);
+                        }
+                }
+
+                rq->rt_throttled = 0;
         }
 }
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index cb89fa8db110..5f9fb645b725 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -153,6 +153,7 @@ void tick_nohz_update_jiffies(void)
 void tick_nohz_stop_sched_tick(void)
 {
         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
+        unsigned long rt_jiffies;
         struct tick_sched *ts;
         ktime_t last_update, expires, now, delta;
         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
@@ -216,6 +217,10 @@ void tick_nohz_stop_sched_tick(void)
         next_jiffies = get_next_timer_interrupt(last_jiffies);
         delta_jiffies = next_jiffies - last_jiffies;
 
+        rt_jiffies = rt_needs_cpu(cpu);
+        if (rt_jiffies && rt_jiffies < delta_jiffies)
+                delta_jiffies = rt_jiffies;
+
         if (rcu_needs_cpu(cpu))
                 delta_jiffies = 1;
         /*