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Subject[PATCH] sched/deadline: Fix sched_dl_global_validate()
When user changes sched_rt_{runtime, period}_us, then

sched_rt_handler()
--> sched_dl_bandwidth_validate()
{
new_bw = global_rt_runtime()/global_rt_period();

for_each_possible_cpu(cpu) {
dl_b = dl_bw_of(cpu);
if (new_bw < dl_b->total_bw)
ret = -EBUSY;
}
}

Under CONFIG_SMP, dl_bw is per root domain , but not per CPU,
dl_b->total_bw is the allocated bandwidth of the whole root domain.
we should compare dl_b->total_bw against cpus*new_bw, where 'cpus'
is the number of CPUs of the root domain.

Also, below annotation(in kernel/sched/sched.h) implied implementation
only appeared in SCHED_DEADLINE v2[1], then deadline scheduler kept
evolving till got merged(v9), but the annotation remains unchanged,
meaningless and misleading, correct it.

* With respect to SMP, the bandwidth is given on a per-CPU basis,
* meaning that:
* - dl_bw (< 100%) is the bandwidth of the system (group) on each CPU;
* - dl_total_bw array contains, in the i-eth element, the currently
* allocated bandwidth on the i-eth CPU.

[1] https://lkml.org/lkml/2010/2/28/119

Signed-off-by: Peng Liu <iwtbavbm@gmail.com>
---
In fact, I'm not 100% sure that's a bug, since it's too 'obvious' and
not newly introduced code.

Also, the introduced #ifdef...#endif pairs look ugly, I have no idea
how to eliminate them. Ideas and comments are welcome. Thanks.

kernel/sched/deadline.c | 48 ++++++++++++++++++++++++++++-------------
kernel/sched/sched.h | 17 +++++----------
2 files changed, 38 insertions(+), 27 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 3862a28cd05d..6524cb31148e 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2511,33 +2511,43 @@ const struct sched_class dl_sched_class
.update_curr = update_curr_dl,
};

+#ifdef CONFIG_SMP
+static struct cpumask dl_local_possible_mask;
+#endif /* CONFIG_SMP */
+
int sched_dl_global_validate(void)
{
u64 runtime = global_rt_runtime();
u64 period = global_rt_period();
u64 new_bw = to_ratio(period, runtime);
struct dl_bw *dl_b;
- int cpu, ret = 0;
+ int cpu, cpus = 1, ret = 0;
unsigned long flags;
-
+ cpumask_t *possible_mask = NULL;
+#ifdef CONFIG_SMP
+ cpumask_t *span;
+#endif /* CONFIG_SMP */
/*
* Here we want to check the bandwidth not being set to some
* value smaller than the currently allocated bandwidth in
* any of the root_domains.
- *
- * FIXME: Cycling on all the CPUs is overdoing, but simpler than
- * cycling on root_domains... Discussion on different/better
- * solutions is welcome!
*/
- for_each_possible_cpu(cpu) {
+#ifdef CONFIG_SMP
+ possible_mask = &dl_local_possible_mask;
+ cpumask_copy(possible_mask, cpu_possible_mask);
+#endif /* CONFIG_SMP */
+ for_each_cpu(cpu, possible_mask) {
rcu_read_lock_sched();
dl_b = dl_bw_of(cpu);
-
+#ifdef CONFIG_SMP
+ span = cpu_rq(cpu)->rd->span;
+ cpus = cpumask_weight(span);
+ cpumask_andnot(possible_mask, possible_mask, span);
+#endif /* CONFIG_SMP */
raw_spin_lock_irqsave(&dl_b->lock, flags);
- if (new_bw < dl_b->total_bw)
+ if (new_bw * cpus < dl_b->total_bw)
ret = -EBUSY;
raw_spin_unlock_irqrestore(&dl_b->lock, flags);
-
rcu_read_unlock_sched();

if (ret)
@@ -2566,6 +2576,10 @@ void sched_dl_do_global(void)
struct dl_bw *dl_b;
int cpu;
unsigned long flags;
+ cpumask_t *possible_mask = NULL;
+#ifdef CONFIG_SMP
+ cpumask_t *span;
+#endif /* CONFIG_SMP */

def_dl_bandwidth.dl_period = global_rt_period();
def_dl_bandwidth.dl_runtime = global_rt_runtime();
@@ -2573,17 +2587,21 @@ void sched_dl_do_global(void)
if (global_rt_runtime() != RUNTIME_INF)
new_bw = to_ratio(global_rt_period(), global_rt_runtime());

- /*
- * FIXME: As above...
- */
- for_each_possible_cpu(cpu) {
+#ifdef CONFIG_SMP
+ possible_mask = &dl_local_possible_mask;
+ cpumask_copy(possible_mask, cpu_possible_mask);
+#endif /* CONFIG_SMP */
+ for_each_cpu(cpu, possible_mask) {
rcu_read_lock_sched();
dl_b = dl_bw_of(cpu);

raw_spin_lock_irqsave(&dl_b->lock, flags);
dl_b->bw = new_bw;
raw_spin_unlock_irqrestore(&dl_b->lock, flags);
-
+#ifdef CONFIG_SMP
+ span = cpu_rq(cpu)->rd->span;
+ cpumask_andnot(possible_mask, possible_mask, span);
+#endif /* CONFIG_SMP */
rcu_read_unlock_sched();
init_dl_rq_bw_ratio(&cpu_rq(cpu)->dl);
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 28709f6b0975..2602544e06ff 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -258,9 +258,9 @@ struct rt_bandwidth {
void __dl_clear_params(struct task_struct *p);

/*
- * To keep the bandwidth of -deadline tasks and groups under control
+ * To keep the bandwidth of -deadline tasks under control
* we need some place where:
- * - store the maximum -deadline bandwidth of the system (the group);
+ * - store the maximum -deadline bandwidth of each root domain;
* - cache the fraction of that bandwidth that is currently allocated.
*
* This is all done in the data structure below. It is similar to the
@@ -269,17 +269,10 @@ void __dl_clear_params(struct task_struct *p);
* do not decrease any runtime while the group "executes", neither we
* need a timer to replenish it.
*
- * With respect to SMP, the bandwidth is given on a per-CPU basis,
+ * With respect to SMP, the bandwidth is given on a per root domain basis,
* meaning that:
- * - dl_bw (< 100%) is the bandwidth of the system (group) on each CPU;
- * - dl_total_bw array contains, in the i-eth element, the currently
- * allocated bandwidth on the i-eth CPU.
- * Moreover, groups consume bandwidth on each CPU, while tasks only
- * consume bandwidth on the CPU they're running on.
- * Finally, dl_total_bw_cpu is used to cache the index of dl_total_bw
- * that will be shown the next time the proc or cgroup controls will
- * be red. It on its turn can be changed by writing on its own
- * control.
+ * - bw (< 100%) is the bandwidth of the system on each CPU;
+ * - total_bw is the currently allocated bandwidth on each root domain.
*/
struct dl_bandwidth {
raw_spinlock_t dl_runtime_lock;
--
2.20.1
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