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Subject[RFC PATCH v2 15/17] sched: Trivial forced-newidle balancer
Date
From: Peter Zijlstra (Intel) <peterz@infradead.org>

When a sibling is forced-idle to match the core-cookie; search for
matching tasks to fill the core.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 131 +++++++++++++++++++++++++++++++++++++++++-
kernel/sched/idle.c | 1 +
kernel/sched/sched.h | 6 ++
4 files changed, 138 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a4b39a28236f..1a309e8546cd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -641,6 +641,7 @@ 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 9e6e90c6f9b9..e8f5ec641d0a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -217,6 +217,21 @@ struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
return match;
}

+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:
*
@@ -3672,7 +3687,7 @@ 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;

if (!sched_core_enabled(rq))
return __pick_next_task(rq, prev, rf);
@@ -3763,6 +3778,9 @@ 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;

/*
@@ -3786,6 +3804,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)

cpu_rq(j)->core_pick = NULL;
}
+ occ = 1;
goto again;
}
}
@@ -3808,6 +3827,8 @@ next_class:;

WARN_ON_ONCE(!rq_i->core_pick);

+ rq_i->core_pick->core_occupation = occ;
+
if (i == cpu)
continue;

@@ -3823,6 +3844,114 @@ 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_allowed))
+ 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);
+
+ rcu_read_lock();
+ raw_spin_unlock_irq(rq_lockp(rq));
+ for_each_domain(cpu, sd) {
+ if (!(sd->flags & SD_LOAD_BALANCE))
+ break;
+
+ if (need_resched())
+ break;
+
+ if (steal_cookie_task(cpu, sd))
+ break;
+ }
+ raw_spin_lock_irq(rq_lockp(rq));
+ rcu_read_unlock();
+}
+
+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 e7f38da60373..44decdcccba1 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -387,6 +387,7 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next)
{
update_idle_core(rq);
schedstat_inc(rq->sched_goidle);
+ queue_core_balance(rq);
}

static struct task_struct *
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4cfde289610d..2a5f5a6b11ae 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1013,6 +1013,8 @@ static inline raw_spinlock_t *rq_lockp(struct rq *rq)
return &rq->__lock;
}

+extern void queue_core_balance(struct rq *rq);
+
#else /* !CONFIG_SCHED_CORE */

static inline bool sched_core_enabled(struct rq *rq)
@@ -1025,6 +1027,10 @@ 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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