sched: rt-group: smp balancing

Currently the rt group scheduling does a per cpu runtime limit, however
the rt load balancer makes no guarantees about an equal spread of real-
time tasks, just that at any one time, the highest priority tasks run.

Solve this by making the runtime limit a global property by borrowing
excessive runtime from the other cpus once the local limit runs out.

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

1 files changed, 37 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index bb20323f7d09..313cd4f057cf 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -164,6 +164,7 @@ struct rt_prio_array {
 struct rt_bandwidth {
         ktime_t rt_period;
         u64 rt_runtime;
+        spinlock_t rt_runtime_lock;
         struct hrtimer rt_period_timer;
 };
 
@@ -198,6 +199,8 @@ void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime)
         rt_b->rt_period = ns_to_ktime(period);
         rt_b->rt_runtime = runtime;
 
+        spin_lock_init(&rt_b->rt_runtime_lock);
+
         hrtimer_init(&rt_b->rt_period_timer,
                         CLOCK_MONOTONIC, HRTIMER_MODE_REL);
         rt_b->rt_period_timer.function = sched_rt_period_timer;
@@ -414,6 +417,8 @@ struct rt_rq {
 #endif
         int rt_throttled;
         u64 rt_time;
+        u64 rt_runtime;
+        spinlock_t rt_runtime_lock;
 
 #ifdef CONFIG_RT_GROUP_SCHED
         unsigned long rt_nr_boosted;
@@ -7299,6 +7304,8 @@ static void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)
 
         rt_rq->rt_time = 0;
         rt_rq->rt_throttled = 0;
+        rt_rq->rt_runtime = 0;
+        spin_lock_init(&rt_rq->rt_runtime_lock);
 
 #ifdef CONFIG_RT_GROUP_SCHED
         rt_rq->rt_nr_boosted = 0;
@@ -7335,6 +7342,7 @@ static void init_tg_rt_entry(struct rq *rq, struct task_group *tg,
         init_rt_rq(rt_rq, rq);
         rt_rq->tg = tg;
         rt_rq->rt_se = rt_se;
+        rt_rq->rt_runtime = tg->rt_bandwidth.rt_runtime;
         if (add)
                 list_add(&rt_rq->leaf_rt_rq_list, &rq->leaf_rt_rq_list);
 
@@ -7391,6 +7399,8 @@ void __init sched_init(void)
                 init_tg_rt_entry(rq, &init_task_group,
                                 &per_cpu(init_rt_rq, i),
                                 &per_cpu(init_sched_rt_entity, i), i, 1);
+#else
+                rq->rt.rt_runtime = def_rt_bandwidth.rt_runtime;
 #endif
 
                 for (j = 0; j < CPU_LOAD_IDX_MAX; j++)
@@ -7974,11 +7984,11 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
 static int tg_set_bandwidth(struct task_group *tg,
                 u64 rt_period, u64 rt_runtime)
 {
-        int err = 0;
+        int i, err = 0;
 
         mutex_lock(&rt_constraints_mutex);
         read_lock(&tasklist_lock);
-        if (rt_runtime_us == 0 && tg_has_rt_tasks(tg)) {
+        if (rt_runtime == 0 && tg_has_rt_tasks(tg)) {
                 err = -EBUSY;
                 goto unlock;
         }
@@ -7986,8 +7996,19 @@ static int tg_set_bandwidth(struct task_group *tg,
                 err = -EINVAL;
                 goto unlock;
         }
+
+        spin_lock_irq(&tg->rt_bandwidth.rt_runtime_lock);
         tg->rt_bandwidth.rt_period = ns_to_ktime(rt_period);
         tg->rt_bandwidth.rt_runtime = rt_runtime;
+
+        for_each_possible_cpu(i) {
+                struct rt_rq *rt_rq = tg->rt_rq[i];
+
+                spin_lock(&rt_rq->rt_runtime_lock);
+                rt_rq->rt_runtime = rt_runtime;
+                spin_unlock(&rt_rq->rt_runtime_lock);
+        }
+        spin_unlock_irq(&tg->rt_bandwidth.rt_runtime_lock);
  unlock:
         read_unlock(&tasklist_lock);
         mutex_unlock(&rt_constraints_mutex);
@@ -8052,6 +8073,19 @@ static int sched_rt_global_constraints(void)
 #else
 static int sched_rt_global_constraints(void)
 {
+        unsigned long flags;
+        int i;
+
+        spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
+        for_each_possible_cpu(i) {
+                struct rt_rq *rt_rq = &cpu_rq(i)->rt;
+
+                spin_lock(&rt_rq->rt_runtime_lock);
+                rt_rq->rt_runtime = global_rt_runtime();
+                spin_unlock(&rt_rq->rt_runtime_lock);
+        }
+        spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
+
         return 0;
 }
 #endif
@@ -8168,7 +8202,7 @@ static u64 cpu_shares_read_uint(struct cgroup *cgrp, struct cftype *cft)
 #endif
 
 #ifdef CONFIG_RT_GROUP_SCHED
-static int cpu_rt_runtime_write(struct cgroup *cgrp, struct cftype *cft,
+static ssize_t cpu_rt_runtime_write(struct cgroup *cgrp, struct cftype *cft,
                                 struct file *file,
                                 const char __user *userbuf,
                                 size_t nbytes, loff_t *unused_ppos)