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Message-ID: <20200917163900.GA29339@iZj6chx1xj0e0buvshuecpZ>
Date: Fri, 18 Sep 2020 00:39:00 +0800
From: Peng Liu <iwtbavbm@...il.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
vincent.guittot@...aro.org, dietmar.eggemann@....com,
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
bristot@...hat.com, valentin.schneider@....com, raistlin@...ux.it,
iwtbavbm@...il.com
Subject: [PATCH v2] 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@...il.com>
---
v2 <-- v1:
Replace cpumask_weight(cpu_rq(cpu)->rd->span) with dl_bw_cpus(cpu),
suggested by Juri.
kernel/sched/deadline.c | 45 +++++++++++++++++++++++++++++------------
kernel/sched/sched.h | 17 +++++-----------
2 files changed, 37 insertions(+), 25 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 3862a28cd05d..17526ecae272 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2511,33 +2511,45 @@ 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, ret = 0;
unsigned long flags;
/*
* 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!
*/
+#ifdef CONFIG_SMP
+ cpumask_t *possible_mask = &dl_local_possible_mask;
+
+ cpumask_copy(possible_mask, cpu_possible_mask);
+ for_each_cpu(cpu, possible_mask) {
+#else
for_each_possible_cpu(cpu) {
+#endif /* CONFIG_SMP */
rcu_read_lock_sched();
dl_b = dl_bw_of(cpu);
-
+ cpus = dl_bw_cpus(cpu);
+#ifdef CONFIG_SMP
+ /* Do the "andnot" operation iff it's necessary. */
+ if (cpus > 1)
+ cpumask_andnot(possible_mask, possible_mask,
+ cpu_rq(cpu)->rd->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 +2578,9 @@ void sched_dl_do_global(void)
struct dl_bw *dl_b;
int cpu;
unsigned long flags;
+#ifdef CONFIG_SMP
+ cpumask_t *possible_mask = NULL;
+#endif /* CONFIG_SMP */
def_dl_bandwidth.dl_period = global_rt_period();
def_dl_bandwidth.dl_runtime = global_rt_runtime();
@@ -2573,17 +2588,21 @@ 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
+ cpumask_andnot(possible_mask, possible_mask,
+ cpu_rq(cpu)->rd->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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