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Date: Fri, 28 Aug 2020 15:51:13 -0400
From: Julien Desfossez <jdesfossez@...italocean.com>
To: Peter Zijlstra <peterz@...radead.org>,
Vineeth Pillai <viremana@...ux.microsoft.com>,
Joel Fernandes <joelaf@...gle.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Aaron Lu <aaron.lwe@...il.com>,
Aubrey Li <aubrey.intel@...il.com>,
Dhaval Giani <dhaval.giani@...cle.com>,
Chris Hyser <chris.hyser@...cle.com>,
Nishanth Aravamudan <naravamudan@...italocean.com>
Cc: mingo@...nel.org, tglx@...utronix.de, pjt@...gle.com,
torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
Phil Auld <pauld@...hat.com>,
Valentin Schneider <valentin.schneider@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>, joel@...lfernandes.org,
vineeth@...byteword.org, Chen Yu <yu.c.chen@...el.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Agata Gruza <agata.gruza@...el.com>,
Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
rostedt@...dmis.org, derkling@...gle.com, benbjiang@...cent.com
Subject: [RFC PATCH v7 12/23] sched: Trivial forced-newidle balancer
From: Peter Zijlstra <peterz@...radead.org>
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>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Acked-by: Paul E. McKenney <paulmck@...nel.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(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5fe9878502cb..eee53fa7b8d4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -687,6 +687,7 @@ 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
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 707a56ef0fa3..7e2f310ec0c0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -201,6 +201,21 @@ static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
return match;
}
+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;
+}
+
/*
* The static-key + stop-machine variable are needed such that:
*
@@ -4641,7 +4656,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
struct task_struct *next, *max = NULL;
const struct sched_class *class;
const struct cpumask *smt_mask;
- int i, j, cpu;
+ int i, j, cpu, occ = 0;
int smt_weight;
bool need_sync;
@@ -4750,6 +4765,9 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
goto done;
}
+ if (!is_idle_task(p))
+ occ++;
+
rq_i->core_pick = p;
/*
@@ -4775,6 +4793,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
cpu_rq(j)->core_pick = NULL;
}
+ occ = 1;
goto again;
} else {
/*
@@ -4820,6 +4839,8 @@ next_class:;
if (is_idle_task(rq_i->core_pick) && rq_i->nr_running)
rq_i->core_forceidle = true;
+ rq_i->core_pick->core_occupation = occ;
+
if (i == cpu)
continue;
@@ -4837,6 +4858,113 @@ next_class:;
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_unlock_irq(rq_lockp(rq));
+ for_each_domain(cpu, sd) {
+ if (need_resched())
+ break;
+
+ if (steal_cookie_task(cpu, sd))
+ break;
+ }
+ raw_spin_lock_irq(rq_lockp(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);
+}
+
#else /* !CONFIG_SCHED_CORE */
static struct task_struct *
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 8c41b023dd14..9c5637d866fd 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -406,6 +406,7 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir
{
update_idle_core(rq);
schedstat_inc(rq->sched_goidle);
+ queue_core_balance(rq);
}
#ifdef CONFIG_SMP
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 7e9346de3f59..be6db45276e7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1109,6 +1109,8 @@ static inline raw_spinlock_t *rq_lockp(struct rq *rq)
bool cfs_prio_less(struct task_struct *a, struct task_struct *b);
void sched_core_adjust_sibling_vruntime(int cpu, bool coresched_enabled);
+extern void queue_core_balance(struct rq *rq);
+
#else /* !CONFIG_SCHED_CORE */
static inline bool sched_core_enabled(struct rq *rq)
@@ -1121,6 +1123,10 @@ static inline raw_spinlock_t *rq_lockp(struct rq *rq)
return &rq->__lock;
}
+static inline void queue_core_balance(struct rq *rq)
+{
+}
+
#endif /* CONFIG_SCHED_CORE */
#ifdef CONFIG_SCHED_SMT
--
2.17.1
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