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sched: rt-group: smp balancing
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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>
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Peter Zijlstra authored and Ingo Molnar committed Apr 19, 2008
1 parent d0b27fa commit ac086bc
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Showing 2 changed files with 122 additions and 6 deletions.
40 changes: 37 additions & 3 deletions kernel/sched.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
};

Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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++)
Expand Down Expand Up @@ -7974,20 +7984,31 @@ 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;
}
if (!__rt_schedulable(tg, rt_period, rt_runtime)) {
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);
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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)
Expand Down
88 changes: 85 additions & 3 deletions kernel/sched_rt.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -62,7 +62,12 @@ static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
if (!rt_rq->tg)
return RUNTIME_INF;

return rt_rq->tg->rt_bandwidth.rt_runtime;
return rt_rq->rt_runtime;
}

static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
}

#define for_each_leaf_rt_rq(rt_rq, rq) \
Expand Down Expand Up @@ -145,11 +150,21 @@ struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
return container_of(rt_b, struct task_group, rt_bandwidth)->rt_rq[cpu];
}

static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
return &rt_rq->tg->rt_bandwidth;
}

#else

static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
return def_rt_bandwidth.rt_runtime;
return rt_rq->rt_runtime;
}

static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
return ktime_to_ns(def_rt_bandwidth.rt_period);
}

#define for_each_leaf_rt_rq(rt_rq, rq) \
Expand Down Expand Up @@ -200,6 +215,11 @@ struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
return &cpu_rq(cpu)->rt;
}

static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
return &def_rt_bandwidth;
}

#endif

static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
Expand All @@ -218,15 +238,18 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)

spin_lock(&rq->lock);
if (rt_rq->rt_time) {
u64 runtime = rt_b->rt_runtime;
u64 runtime;

spin_lock(&rt_rq->rt_runtime_lock);
runtime = rt_rq->rt_runtime;
rt_rq->rt_time -= min(rt_rq->rt_time, overrun*runtime);
if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
rt_rq->rt_throttled = 0;
enqueue = 1;
}
if (rt_rq->rt_time || rt_rq->rt_nr_running)
idle = 0;
spin_unlock(&rt_rq->rt_runtime_lock);
}

if (enqueue)
Expand All @@ -237,6 +260,47 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
return idle;
}

#ifdef CONFIG_SMP
static int balance_runtime(struct rt_rq *rt_rq)
{
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
int i, weight, more = 0;
u64 rt_period;

weight = cpus_weight(rd->span);

spin_lock(&rt_b->rt_runtime_lock);
rt_period = ktime_to_ns(rt_b->rt_period);
for_each_cpu_mask(i, rd->span) {
struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
s64 diff;

if (iter == rt_rq)
continue;

spin_lock(&iter->rt_runtime_lock);
diff = iter->rt_runtime - iter->rt_time;
if (diff > 0) {
do_div(diff, weight);
if (rt_rq->rt_runtime + diff > rt_period)
diff = rt_period - rt_rq->rt_runtime;
iter->rt_runtime -= diff;
rt_rq->rt_runtime += diff;
more = 1;
if (rt_rq->rt_runtime == rt_period) {
spin_unlock(&iter->rt_runtime_lock);
break;
}
}
spin_unlock(&iter->rt_runtime_lock);
}
spin_unlock(&rt_b->rt_runtime_lock);

return more;
}
#endif

static inline int rt_se_prio(struct sched_rt_entity *rt_se)
{
#ifdef CONFIG_RT_GROUP_SCHED
Expand All @@ -259,6 +323,22 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
if (rt_rq->rt_throttled)
return rt_rq_throttled(rt_rq);

if (sched_rt_runtime(rt_rq) >= sched_rt_period(rt_rq))
return 0;

#ifdef CONFIG_SMP
if (rt_rq->rt_time > runtime) {
int more;

spin_unlock(&rt_rq->rt_runtime_lock);
more = balance_runtime(rt_rq);
spin_lock(&rt_rq->rt_runtime_lock);

if (more)
runtime = sched_rt_runtime(rt_rq);
}
#endif

if (rt_rq->rt_time > runtime) {
rt_rq->rt_throttled = 1;
if (rt_rq_throttled(rt_rq)) {
Expand Down Expand Up @@ -294,9 +374,11 @@ static void update_curr_rt(struct rq *rq)
curr->se.exec_start = rq->clock;
cpuacct_charge(curr, delta_exec);

spin_lock(&rt_rq->rt_runtime_lock);
rt_rq->rt_time += delta_exec;
if (sched_rt_runtime_exceeded(rt_rq))
resched_task(curr);
spin_unlock(&rt_rq->rt_runtime_lock);
}

static inline
Expand Down

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