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Message-ID: <20210422123308.800048269@infradead.org>
Date: Thu, 22 Apr 2021 14:05:13 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: joel@...lfernandes.org, chris.hyser@...cle.com, joshdon@...gle.com,
mingo@...nel.org, vincent.guittot@...aro.org,
valentin.schneider@....com, mgorman@...e.de
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
tglx@...utronix.de
Subject: [PATCH 14/19] sched: Trivial forced-newidle balancer
When a sibling is forced-idle to match the core-cookie; search for
matching tasks to fill the core.
rcu_read_unlock() can incur an infrequent deadlock in
sched_core_balance(). Fix this by using the RCU-sched flavor instead.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
include/linux/sched.h | 1
kernel/sched/core.c | 130 +++++++++++++++++++++++++++++++++++++++++++++++++-
kernel/sched/idle.c | 1
kernel/sched/sched.h | 6 ++
4 files changed, 137 insertions(+), 1 deletion(-)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -704,6 +704,7 @@ struct task_struct {
#ifdef CONFIG_SCHED_CORE
struct rb_node core_node;
unsigned long core_cookie;
+ unsigned int core_occupation;
#endif
#ifdef CONFIG_CGROUP_SCHED
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -204,6 +204,21 @@ static struct task_struct *sched_core_fi
return __node_2_sc(node);
}
+static struct task_struct *sched_core_next(struct task_struct *p, unsigned long cookie)
+{
+ struct rb_node *node = &p->core_node;
+
+ node = rb_next(node);
+ if (!node)
+ return NULL;
+
+ p = container_of(node, struct task_struct, core_node);
+ if (p->core_cookie != cookie)
+ return NULL;
+
+ return p;
+}
+
/*
* Magic required such that:
*
@@ -5371,8 +5386,8 @@ pick_next_task(struct rq *rq, struct tas
const struct sched_class *class;
const struct cpumask *smt_mask;
bool fi_before = false;
+ int i, j, cpu, occ = 0;
bool need_sync;
- int i, j, cpu;
if (!sched_core_enabled(rq))
return __pick_next_task(rq, prev, rf);
@@ -5494,6 +5509,9 @@ pick_next_task(struct rq *rq, struct tas
if (!p)
continue;
+ if (!is_task_rq_idle(p))
+ occ++;
+
rq_i->core_pick = p;
if (rq_i->idle == p && rq_i->nr_running) {
rq->core->core_forceidle = true;
@@ -5525,6 +5543,7 @@ pick_next_task(struct rq *rq, struct tas
cpu_rq(j)->core_pick = NULL;
}
+ occ = 1;
goto again;
}
}
@@ -5570,6 +5589,8 @@ pick_next_task(struct rq *rq, struct tas
if (!(fi_before && rq->core->core_forceidle))
task_vruntime_update(rq_i, rq_i->core_pick, rq->core->core_forceidle);
+ rq_i->core_pick->core_occupation = occ;
+
if (i == cpu) {
rq_i->core_pick = NULL;
continue;
@@ -5591,6 +5612,113 @@ pick_next_task(struct rq *rq, struct tas
return next;
}
+static bool try_steal_cookie(int this, int that)
+{
+ struct rq *dst = cpu_rq(this), *src = cpu_rq(that);
+ struct task_struct *p;
+ unsigned long cookie;
+ bool success = false;
+
+ local_irq_disable();
+ double_rq_lock(dst, src);
+
+ cookie = dst->core->core_cookie;
+ if (!cookie)
+ goto unlock;
+
+ if (dst->curr != dst->idle)
+ goto unlock;
+
+ p = sched_core_find(src, cookie);
+ if (p == src->idle)
+ goto unlock;
+
+ do {
+ if (p == src->core_pick || p == src->curr)
+ goto next;
+
+ if (!cpumask_test_cpu(this, &p->cpus_mask))
+ goto next;
+
+ if (p->core_occupation > dst->idle->core_occupation)
+ goto next;
+
+ p->on_rq = TASK_ON_RQ_MIGRATING;
+ deactivate_task(src, p, 0);
+ set_task_cpu(p, this);
+ activate_task(dst, p, 0);
+ p->on_rq = TASK_ON_RQ_QUEUED;
+
+ resched_curr(dst);
+
+ success = true;
+ break;
+
+next:
+ p = sched_core_next(p, cookie);
+ } while (p);
+
+unlock:
+ double_rq_unlock(dst, src);
+ local_irq_enable();
+
+ return success;
+}
+
+static bool steal_cookie_task(int cpu, struct sched_domain *sd)
+{
+ int i;
+
+ for_each_cpu_wrap(i, sched_domain_span(sd), cpu) {
+ if (i == cpu)
+ continue;
+
+ if (need_resched())
+ break;
+
+ if (try_steal_cookie(cpu, i))
+ return true;
+ }
+
+ return false;
+}
+
+static void sched_core_balance(struct rq *rq)
+{
+ struct sched_domain *sd;
+ int cpu = cpu_of(rq);
+
+ preempt_disable();
+ rcu_read_lock();
+ raw_spin_rq_unlock_irq(rq);
+ for_each_domain(cpu, sd) {
+ if (need_resched())
+ break;
+
+ if (steal_cookie_task(cpu, sd))
+ break;
+ }
+ raw_spin_rq_lock_irq(rq);
+ rcu_read_unlock();
+ preempt_enable();
+}
+
+static DEFINE_PER_CPU(struct callback_head, core_balance_head);
+
+void queue_core_balance(struct rq *rq)
+{
+ if (!sched_core_enabled(rq))
+ return;
+
+ if (!rq->core->core_cookie)
+ return;
+
+ if (!rq->nr_running) /* not forced idle */
+ return;
+
+ queue_balance_callback(rq, &per_cpu(core_balance_head, rq->cpu), sched_core_balance);
+}
+
static inline void sched_core_cpu_starting(unsigned int cpu)
{
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -437,6 +437,7 @@ static void set_next_task_idle(struct rq
{
update_idle_core(rq);
schedstat_inc(rq->sched_goidle);
+ queue_core_balance(rq);
}
#ifdef CONFIG_SMP
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1170,6 +1170,8 @@ static inline raw_spinlock_t *__rq_lockp
bool cfs_prio_less(struct task_struct *a, struct task_struct *b, bool fi);
+extern void queue_core_balance(struct rq *rq);
+
#else /* !CONFIG_SCHED_CORE */
static inline bool sched_core_enabled(struct rq *rq)
@@ -1187,6 +1189,10 @@ static inline raw_spinlock_t *rq_lockp(s
return &rq->__lock;
}
+static inline void queue_core_balance(struct rq *rq)
+{
+}
+
#endif /* CONFIG_SCHED_CORE */
static inline void lockdep_assert_rq_held(struct rq *rq)
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