sched: rt-group: synchonised bandwidth period

Various SMP balancing algorithms require that the bandwidth period
run in sync.

Possible improvements are moving the rt_bandwidth thing into root_domain
and keeping a span per rt_bandwidth which marks throttled cpus.

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

1 files changed, 211 insertions, 49 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index e813e84..bb20323 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -115,6 +115,11 @@ unsigned long long __attribute__((weak)) sched_clock(void)
  */
 #define DEF_TIMESLICE		(100 * HZ / 1000)
 
+/*
+ * single value that denotes runtime == period, ie unlimited time.
+ */
+#define RUNTIME_INF	((u64)~0ULL)
+
 #ifdef CONFIG_SMP
 /*
  * Divide a load by a sched group cpu_power : (load / sg->__cpu_power)
@@ -156,6 +161,80 @@ struct rt_prio_array {
 	struct list_head queue[MAX_RT_PRIO];
 };
 
+struct rt_bandwidth {
+	ktime_t rt_period;
+	u64 rt_runtime;
+	struct hrtimer rt_period_timer;
+};
+
+static struct rt_bandwidth def_rt_bandwidth;
+
+static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);
+
+static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
+{
+	struct rt_bandwidth *rt_b =
+		container_of(timer, struct rt_bandwidth, rt_period_timer);
+	ktime_t now;
+	int overrun;
+	int idle = 0;
+
+	for (;;) {
+		now = hrtimer_cb_get_time(timer);
+		overrun = hrtimer_forward(timer, now, rt_b->rt_period);
+
+		if (!overrun)
+			break;
+
+		idle = do_sched_rt_period_timer(rt_b, overrun);
+	}
+
+	return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
+}
+
+static
+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;
+
+	hrtimer_init(&rt_b->rt_period_timer,
+			CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	rt_b->rt_period_timer.function = sched_rt_period_timer;
+	rt_b->rt_period_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+}
+
+static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
+{
+	ktime_t now;
+
+	if (rt_b->rt_runtime == RUNTIME_INF)
+		return;
+
+	if (hrtimer_active(&rt_b->rt_period_timer))
+		return;
+
+	spin_lock(&rt_b->rt_runtime_lock);
+	for (;;) {
+		if (hrtimer_active(&rt_b->rt_period_timer))
+			break;
+
+		now = hrtimer_cb_get_time(&rt_b->rt_period_timer);
+		hrtimer_forward(&rt_b->rt_period_timer, now, rt_b->rt_period);
+		hrtimer_start(&rt_b->rt_period_timer,
+			      rt_b->rt_period_timer.expires,
+			      HRTIMER_MODE_ABS);
+	}
+	spin_unlock(&rt_b->rt_runtime_lock);
+}
+
+#ifdef CONFIG_RT_GROUP_SCHED
+static void destroy_rt_bandwidth(struct rt_bandwidth *rt_b)
+{
+	hrtimer_cancel(&rt_b->rt_period_timer);
+}
+#endif
+
 #ifdef CONFIG_GROUP_SCHED
 
 #include <linux/cgroup.h>
@@ -182,7 +261,7 @@ struct task_group {
 	struct sched_rt_entity **rt_se;
 	struct rt_rq **rt_rq;
 
-	u64 rt_runtime;
+	struct rt_bandwidth rt_bandwidth;
 #endif
 
 	struct rcu_head rcu;
@@ -407,8 +486,6 @@ 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: */
@@ -592,23 +669,6 @@ 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:
  */
@@ -664,10 +724,18 @@ static __read_mostly int scheduler_running;
  */
 int sysctl_sched_rt_runtime = 950000;
 
-/*
- * single value that denotes runtime == period, ie unlimited time.
- */
-#define RUNTIME_INF	((u64)~0ULL)
+static inline u64 global_rt_period(void)
+{
+	return (u64)sysctl_sched_rt_period * NSEC_PER_USEC;
+}
+
+static inline u64 global_rt_runtime(void)
+{
+	if (sysctl_sched_rt_period < 0)
+		return RUNTIME_INF;
+
+	return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
+}
 
 static const unsigned long long time_sync_thresh = 100000;
 
@@ -3854,7 +3922,6 @@ void scheduler_tick(void)
 	update_last_tick_seen(rq);
 	update_cpu_load(rq);
 	curr->sched_class->task_tick(rq, curr, 0);
-	update_sched_rt_period(rq);
 	spin_unlock(&rq->lock);
 
 #ifdef CONFIG_SMP
@@ -4689,7 +4756,7 @@ recheck:
 	 * Do not allow realtime tasks into groups that have no runtime
 	 * assigned.
 	 */
-	if (rt_policy(policy) && task_group(p)->rt_runtime == 0)
+	if (rt_policy(policy) && task_group(p)->rt_bandwidth.rt_runtime == 0)
 		return -EPERM;
 #endif
 
@@ -7288,6 +7355,14 @@ void __init sched_init(void)
 	init_defrootdomain();
 #endif
 
+	init_rt_bandwidth(&def_rt_bandwidth,
+			global_rt_period(), global_rt_runtime());
+
+#ifdef CONFIG_RT_GROUP_SCHED
+	init_rt_bandwidth(&init_task_group.rt_bandwidth,
+			global_rt_period(), global_rt_runtime());
+#endif
+
 #ifdef CONFIG_GROUP_SCHED
 	list_add(&init_task_group.list, &task_groups);
 #endif
@@ -7312,15 +7387,11 @@ void __init sched_init(void)
 
 #endif
 #ifdef CONFIG_RT_GROUP_SCHED
-		init_task_group.rt_runtime =
-			sysctl_sched_rt_runtime * NSEC_PER_USEC;
 		INIT_LIST_HEAD(&rq->leaf_rt_rq_list);
 		init_tg_rt_entry(rq, &init_task_group,
 				&per_cpu(init_rt_rq, i),
 				&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;
@@ -7506,8 +7577,6 @@ void set_curr_task(int cpu, struct task_struct *p)
 
 #endif
 
-#ifdef CONFIG_GROUP_SCHED
-
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static void free_fair_sched_group(struct task_group *tg)
 {
@@ -7596,6 +7665,8 @@ static void free_rt_sched_group(struct task_group *tg)
 {
 	int i;
 
+	destroy_rt_bandwidth(&tg->rt_bandwidth);
+
 	for_each_possible_cpu(i) {
 		if (tg->rt_rq)
 			kfree(tg->rt_rq[i]);
@@ -7621,7 +7692,8 @@ static int alloc_rt_sched_group(struct task_group *tg)
 	if (!tg->rt_se)
 		goto err;
 
-	tg->rt_runtime = 0;
+	init_rt_bandwidth(&tg->rt_bandwidth,
+			ktime_to_ns(def_rt_bandwidth.rt_period), 0);
 
 	for_each_possible_cpu(i) {
 		rq = cpu_rq(i);
@@ -7674,6 +7746,7 @@ static inline void unregister_rt_sched_group(struct task_group *tg, int cpu)
 }
 #endif
 
+#ifdef CONFIG_GROUP_SCHED
 static void free_sched_group(struct task_group *tg)
 {
 	free_fair_sched_group(tg);
@@ -7775,6 +7848,7 @@ void sched_move_task(struct task_struct *tsk)
 
 	task_rq_unlock(rq, &flags);
 }
+#endif
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static void set_se_shares(struct sched_entity *se, unsigned long shares)
@@ -7871,16 +7945,15 @@ static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
 	struct task_group *tgi;
 	unsigned long total = 0;
 	unsigned long global_ratio =
-		to_ratio(sysctl_sched_rt_period,
-			 sysctl_sched_rt_runtime < 0 ?
-				RUNTIME_INF : sysctl_sched_rt_runtime);
+		to_ratio(global_rt_period(), global_rt_runtime());
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(tgi, &task_groups, list) {
 		if (tgi == tg)
 			continue;
 
-		total += to_ratio(period, tgi->rt_runtime);
+		total += to_ratio(ktime_to_ns(tgi->rt_bandwidth.rt_period),
+				tgi->rt_bandwidth.rt_runtime);
 	}
 	rcu_read_unlock();
 
@@ -7898,16 +7971,11 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
 	return 0;
 }
 
-int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
+static int tg_set_bandwidth(struct task_group *tg,
+		u64 rt_period, u64 rt_runtime)
 {
-	u64 rt_runtime, rt_period;
 	int err = 0;
 
-	rt_period = (u64)sysctl_sched_rt_period * NSEC_PER_USEC;
-	rt_runtime = (u64)rt_runtime_us * NSEC_PER_USEC;
-	if (rt_runtime_us == -1)
-		rt_runtime = RUNTIME_INF;
-
 	mutex_lock(&rt_constraints_mutex);
 	read_lock(&tasklist_lock);
 	if (rt_runtime_us == 0 && tg_has_rt_tasks(tg)) {
@@ -7918,7 +7986,8 @@ int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
 		err = -EINVAL;
 		goto unlock;
 	}
-	tg->rt_runtime = rt_runtime;
+	tg->rt_bandwidth.rt_period = ns_to_ktime(rt_period);
+	tg->rt_bandwidth.rt_runtime = rt_runtime;
  unlock:
 	read_unlock(&tasklist_lock);
 	mutex_unlock(&rt_constraints_mutex);
@@ -7926,19 +7995,96 @@ int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
 	return err;
 }
 
+int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
+{
+	u64 rt_runtime, rt_period;
+
+	rt_period = ktime_to_ns(tg->rt_bandwidth.rt_period);
+	rt_runtime = (u64)rt_runtime_us * NSEC_PER_USEC;
+	if (rt_runtime_us < 0)
+		rt_runtime = RUNTIME_INF;
+
+	return tg_set_bandwidth(tg, rt_period, rt_runtime);
+}
+
 long sched_group_rt_runtime(struct task_group *tg)
 {
 	u64 rt_runtime_us;
 
-	if (tg->rt_runtime == RUNTIME_INF)
+	if (tg->rt_bandwidth.rt_runtime == RUNTIME_INF)
 		return -1;
 
-	rt_runtime_us = tg->rt_runtime;
+	rt_runtime_us = tg->rt_bandwidth.rt_runtime;
 	do_div(rt_runtime_us, NSEC_PER_USEC);
 	return rt_runtime_us;
 }
+
+int sched_group_set_rt_period(struct task_group *tg, long rt_period_us)
+{
+	u64 rt_runtime, rt_period;
+
+	rt_period = (u64)rt_period_us * NSEC_PER_USEC;
+	rt_runtime = tg->rt_bandwidth.rt_runtime;
+
+	return tg_set_bandwidth(tg, rt_period, rt_runtime);
+}
+
+long sched_group_rt_period(struct task_group *tg)
+{
+	u64 rt_period_us;
+
+	rt_period_us = ktime_to_ns(tg->rt_bandwidth.rt_period);
+	do_div(rt_period_us, NSEC_PER_USEC);
+	return rt_period_us;
+}
+
+static int sched_rt_global_constraints(void)
+{
+	int ret = 0;
+
+	mutex_lock(&rt_constraints_mutex);
+	if (!__rt_schedulable(NULL, 1, 0))
+		ret = -EINVAL;
+	mutex_unlock(&rt_constraints_mutex);
+
+	return ret;
+}
+#else
+static int sched_rt_global_constraints(void)
+{
+	return 0;
+}
 #endif
-#endif	/* CONFIG_GROUP_SCHED */
+
+int sched_rt_handler(struct ctl_table *table, int write,
+		struct file *filp, void __user *buffer, size_t *lenp,
+		loff_t *ppos)
+{
+	int ret;
+	int old_period, old_runtime;
+	static DEFINE_MUTEX(mutex);
+
+	mutex_lock(&mutex);
+	old_period = sysctl_sched_rt_period;
+	old_runtime = sysctl_sched_rt_runtime;
+
+	ret = proc_dointvec(table, write, filp, buffer, lenp, ppos);
+
+	if (!ret && write) {
+		ret = sched_rt_global_constraints();
+		if (ret) {
+			sysctl_sched_rt_period = old_period;
+			sysctl_sched_rt_runtime = old_runtime;
+		} else {
+			def_rt_bandwidth.rt_runtime = global_rt_runtime();
+			def_rt_bandwidth.rt_period =
+				ns_to_ktime(global_rt_period());
+		}
+	}
+	mutex_unlock(&mutex);
+
+	return ret;
+}
 
 #ifdef CONFIG_CGROUP_SCHED
 
@@ -7988,7 +8134,7 @@ cpu_cgroup_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
 {
 #ifdef CONFIG_RT_GROUP_SCHED
 	/* Don't accept realtime tasks when there is no way for them to run */
-	if (rt_task(tsk) && cgroup_tg(cgrp)->rt_runtime == 0)
+	if (rt_task(tsk) && cgroup_tg(cgrp)->rt_bandwidth.rt_runtime == 0)
 		return -EINVAL;
 #else
 	/* We don't support RT-tasks being in separate groups */
@@ -8066,6 +8212,17 @@ static ssize_t cpu_rt_runtime_read(struct cgroup *cgrp, struct cftype *cft,
 
 	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
 }
+
+static int cpu_rt_period_write_uint(struct cgroup *cgrp, struct cftype *cftype,
+		u64 rt_period_us)
+{
+	return sched_group_set_rt_period(cgroup_tg(cgrp), rt_period_us);
+}
+
+static u64 cpu_rt_period_read_uint(struct cgroup *cgrp, struct cftype *cft)
+{
+	return sched_group_rt_period(cgroup_tg(cgrp));
+}
 #endif
 
 static struct cftype cpu_files[] = {
@@ -8082,6 +8239,11 @@ static struct cftype cpu_files[] = {
 		.read = cpu_rt_runtime_read,
 		.write = cpu_rt_runtime_write,
 	},
+	{
+		.name = "rt_period_us",
+		.read_uint = cpu_rt_period_read_uint,
+		.write_uint = cpu_rt_period_write_uint,
+	},
 #endif
 };