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Message-ID: <159231011178.16989.2586072790400652946.tip-bot2@tip-bot2>
Date: Tue, 16 Jun 2020 12:21:51 -0000
From: "tip-bot2 for Luca Abeni" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Luca Abeni <luca.abeni@...tannapisa.it>,
Dietmar Eggemann <dietmar.eggemann@....com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>, x86 <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/core] sched/deadline: Improve admission control for
asymmetric CPU capacities
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 60ffd5edc5e4fa69622c125c54ef8e7d5d894af8
Gitweb: https://git.kernel.org/tip/60ffd5edc5e4fa69622c125c54ef8e7d5d894af8
Author: Luca Abeni <luca.abeni@...tannapisa.it>
AuthorDate: Wed, 20 May 2020 15:42:41 +02:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 15 Jun 2020 14:10:05 +02:00
sched/deadline: Improve admission control for asymmetric CPU capacities
The current SCHED_DEADLINE (DL) admission control ensures that
sum of reserved CPU bandwidth < x * M
where
x = /proc/sys/kernel/sched_rt_{runtime,period}_us
M = # CPUs in root domain.
DL admission control works well for homogeneous systems where the
capacity of all CPUs are equal (1024). I.e. bounded tardiness for DL
and non-starvation of non-DL tasks is guaranteed.
But on heterogeneous systems where capacity of CPUs are different it
could fail by over-allocating CPU time on smaller capacity CPUs.
On an Arm big.LITTLE/DynamIQ system DL tasks can easily starve other
tasks making it unusable.
Fix this by explicitly considering the CPU capacity in the DL admission
test by replacing M with the root domain CPU capacity sum.
Signed-off-by: Luca Abeni <luca.abeni@...tannapisa.it>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Juri Lelli <juri.lelli@...hat.com>
Link: https://lkml.kernel.org/r/20200520134243.19352-4-dietmar.eggemann@arm.com
---
kernel/sched/deadline.c | 30 +++++++++++++++++-------------
kernel/sched/sched.h | 6 +++---
2 files changed, 20 insertions(+), 16 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 01f474a..9ebd0a9 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2590,11 +2590,12 @@ void sched_dl_do_global(void)
int sched_dl_overflow(struct task_struct *p, int policy,
const struct sched_attr *attr)
{
- struct dl_bw *dl_b = dl_bw_of(task_cpu(p));
u64 period = attr->sched_period ?: attr->sched_deadline;
u64 runtime = attr->sched_runtime;
u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0;
- int cpus, err = -1;
+ int cpus, err = -1, cpu = task_cpu(p);
+ struct dl_bw *dl_b = dl_bw_of(cpu);
+ unsigned long cap;
if (attr->sched_flags & SCHED_FLAG_SUGOV)
return 0;
@@ -2609,15 +2610,17 @@ int sched_dl_overflow(struct task_struct *p, int policy,
* allocated bandwidth of the container.
*/
raw_spin_lock(&dl_b->lock);
- cpus = dl_bw_cpus(task_cpu(p));
+ cpus = dl_bw_cpus(cpu);
+ cap = dl_bw_capacity(cpu);
+
if (dl_policy(policy) && !task_has_dl_policy(p) &&
- !__dl_overflow(dl_b, cpus, 0, new_bw)) {
+ !__dl_overflow(dl_b, cap, 0, new_bw)) {
if (hrtimer_active(&p->dl.inactive_timer))
__dl_sub(dl_b, p->dl.dl_bw, cpus);
__dl_add(dl_b, new_bw, cpus);
err = 0;
} else if (dl_policy(policy) && task_has_dl_policy(p) &&
- !__dl_overflow(dl_b, cpus, p->dl.dl_bw, new_bw)) {
+ !__dl_overflow(dl_b, cap, p->dl.dl_bw, new_bw)) {
/*
* XXX this is slightly incorrect: when the task
* utilization decreases, we should delay the total
@@ -2772,19 +2775,19 @@ bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr)
#ifdef CONFIG_SMP
int dl_task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed)
{
+ unsigned long flags, cap;
unsigned int dest_cpu;
struct dl_bw *dl_b;
bool overflow;
- int cpus, ret;
- unsigned long flags;
+ int ret;
dest_cpu = cpumask_any_and(cpu_active_mask, cs_cpus_allowed);
rcu_read_lock_sched();
dl_b = dl_bw_of(dest_cpu);
raw_spin_lock_irqsave(&dl_b->lock, flags);
- cpus = dl_bw_cpus(dest_cpu);
- overflow = __dl_overflow(dl_b, cpus, 0, p->dl.dl_bw);
+ cap = dl_bw_capacity(dest_cpu);
+ overflow = __dl_overflow(dl_b, cap, 0, p->dl.dl_bw);
if (overflow) {
ret = -EBUSY;
} else {
@@ -2794,6 +2797,8 @@ int dl_task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allo
* We will free resources in the source root_domain
* later on (see set_cpus_allowed_dl()).
*/
+ int cpus = dl_bw_cpus(dest_cpu);
+
__dl_add(dl_b, p->dl.dl_bw, cpus);
ret = 0;
}
@@ -2826,16 +2831,15 @@ int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur,
bool dl_cpu_busy(unsigned int cpu)
{
- unsigned long flags;
+ unsigned long flags, cap;
struct dl_bw *dl_b;
bool overflow;
- int cpus;
rcu_read_lock_sched();
dl_b = dl_bw_of(cpu);
raw_spin_lock_irqsave(&dl_b->lock, flags);
- cpus = dl_bw_cpus(cpu);
- overflow = __dl_overflow(dl_b, cpus, 0, 0);
+ cap = dl_bw_capacity(cpu);
+ overflow = __dl_overflow(dl_b, cap, 0, 0);
raw_spin_unlock_irqrestore(&dl_b->lock, flags);
rcu_read_unlock_sched();
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 8d5d068..91b250f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -310,11 +310,11 @@ void __dl_add(struct dl_bw *dl_b, u64 tsk_bw, int cpus)
__dl_update(dl_b, -((s32)tsk_bw / cpus));
}
-static inline
-bool __dl_overflow(struct dl_bw *dl_b, int cpus, u64 old_bw, u64 new_bw)
+static inline bool __dl_overflow(struct dl_bw *dl_b, unsigned long cap,
+ u64 old_bw, u64 new_bw)
{
return dl_b->bw != -1 &&
- dl_b->bw * cpus < dl_b->total_bw - old_bw + new_bw;
+ cap_scale(dl_b->bw, cap) < dl_b->total_bw - old_bw + new_bw;
}
extern void init_dl_bw(struct dl_bw *dl_b);
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