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Subject[PATCH 2/3] sched/deadline: Make dl_cpuset_cpumask_can_shrink() capacity-aware
Date
dl_cpuset_cpumask_can_shrink() is used to validate whether there is
still enough CPU capacity for DL tasks in the reduced cpuset.

Currently it still operates on `# remaining CPUs in the cpuset` (1).
Change this to use the already capacity-aware DL admission control
__dl_overflow() for the `cpumask can shrink` test.

dl_b->bw = sched_rt_period << BW_SHIFT / sched_rt_period

dl_b->bw * (1) >= currently allocated bandwidth in root_domain (rd)

Replace (1) w/ `\Sum CPU capacity in rd >> SCHED_CAPACITY_SHIFT`

Adapt __dl_bw_capacity() to take a cpumask instead of a CPU number
argument so that `rd->span` and `cpumask of the reduced cpuset` can
be used here.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---
kernel/sched/deadline.c | 24 +++++++++++-------------
1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 3f9d90b8a8b6..34de6060dea6 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -124,15 +124,12 @@ static inline int dl_bw_cpus(int i)
return cpus;
}

-static inline unsigned long __dl_bw_capacity(int i)
+static inline unsigned long __dl_bw_capacity(const struct cpumask *mask)
{
- struct root_domain *rd = cpu_rq(i)->rd;
unsigned long cap = 0;
+ int i;

- RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
- "sched RCU must be held");
-
- for_each_cpu_and(i, rd->span, cpu_active_mask)
+ for_each_cpu_and(i, mask, cpu_active_mask)
cap += capacity_orig_of(i);

return cap;
@@ -148,7 +145,10 @@ static inline unsigned long dl_bw_capacity(int i)
capacity_orig_of(i) == SCHED_CAPACITY_SCALE) {
return dl_bw_cpus(i) << SCHED_CAPACITY_SHIFT;
} else {
- return __dl_bw_capacity(i);
+ RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
+ "sched RCU must be held");
+
+ return __dl_bw_capacity(cpu_rq(i)->rd->span);
}
}

@@ -3004,17 +3004,15 @@ bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr)
int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur,
const struct cpumask *trial)
{
- int ret = 1, trial_cpus;
+ unsigned long flags, cap;
struct dl_bw *cur_dl_b;
- unsigned long flags;
+ int ret = 1;

rcu_read_lock_sched();
cur_dl_b = dl_bw_of(cpumask_any(cur));
- trial_cpus = cpumask_weight(trial);
-
+ cap = __dl_bw_capacity(trial);
raw_spin_lock_irqsave(&cur_dl_b->lock, flags);
- if (cur_dl_b->bw != -1 &&
- cur_dl_b->bw * trial_cpus < cur_dl_b->total_bw)
+ if (__dl_overflow(cur_dl_b, cap, 0, 0))
ret = 0;
raw_spin_unlock_irqrestore(&cur_dl_b->lock, flags);
rcu_read_unlock_sched();
--
2.25.1
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