From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>,
Qais Yousef <qais.yousef@arm.com>, Scott Wood <swood@redhat.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Vincent Donnefort <vincent.donnefort@arm.com>
Subject: [patch 10/10] sched/core: Make migrate disable and CPU hotplug cooperative
Date: Thu, 17 Sep 2020 11:42:12 +0200 [thread overview]
Message-ID: <20200917101624.907536563@linutronix.de> (raw)
In-Reply-To: 20200917094202.301694311@linutronix.de
On CPU unplug tasks which are in a migrate disabled region cannot be pushed
to a different CPU until they returned to migrateable state.
Account the number of tasks on a runqueue which are in a migrate disabled
section and make the hotplug wait mechanism respect that.
Originally-by: Scott Wood <swood@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/sched/core.c | 38 ++++++++++++++++++++++++++++++++++----
kernel/sched/sched.h | 4 ++++
2 files changed, 38 insertions(+), 4 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -494,6 +494,11 @@ static bool task_self_migration(struct t
return true;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return rq->nr_pinned > 0;
+}
+
#else /* defined(CONFIG_SMP) && defined(CONFIG_PREEMPT_RT) */
static inline void task_lock_migration_ctrl(struct task_struct *p) { }
static inline void task_unlock_migration_ctrl(struct task_struct *p) { }
@@ -504,6 +509,10 @@ static bool task_self_migration(struct t
{
return false;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return false;
+}
#endif /* !(defined(CONFIG_SMP) && defined(CONFIG_PREEMPT_RT)) */
/*
@@ -3591,6 +3600,12 @@ void migrate_disable(void)
if (!current->migration_ctrl.disable_cnt) {
raw_spin_lock_irqsave(¤t->pi_lock, flags);
current->migration_ctrl.disable_cnt++;
+ /*
+ * Account the pinned task in the runqueue so that an
+ * eventual CPU hot unplug operation will wait until
+ * this task left the migrate disabled section.
+ */
+ this_rq()->nr_pinned++;
raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
} else {
current->migration_ctrl.disable_cnt++;
@@ -3619,6 +3634,13 @@ void migrate_enable(void)
p->migration_ctrl.pending = NULL;
/*
+ * Adjust the number of pinned tasks in the runqueue. No further
+ * action required here. An eventually waiting CPU hot unplug
+ * operation will be woken up once the CPU goes through idle.
+ */
+ this_rq()->nr_pinned--;
+
+ /*
* If the task was never scheduled out while in the migrate
* disabled region and there is no migration request pending,
* return.
@@ -6989,8 +7011,13 @@ static bool balance_push(struct rq *rq)
* last task to vanish. The rcuwait_active() check is
* accurate here because the waiter is pinned on this CPU
* and can't obviously be running in parallel.
+ *
+ * On RT kernels this also has to check whether there are
+ * pinned and scheduled out tasks on the runqueue. They
+ * need to leave the migrate disabled section first.
*/
- if (!rq->nr_running && rcuwait_active(&rq->hotplug_wait)) {
+ if (!rq->nr_running && !rq_has_pinned_tasks(rq) &&
+ rcuwait_active(&rq->hotplug_wait)) {
raw_spin_unlock(&rq->lock);
rcuwait_wake_up(&rq->hotplug_wait);
raw_spin_lock(&rq->lock);
@@ -7033,13 +7060,16 @@ static void balance_push_set(int cpu, bo
* Invoked from a CPUs hotplug control thread after the CPU has been marked
* inactive. All tasks which are not per CPU kernel threads are either
* pushed off this CPU now via balance_push() or placed on a different CPU
- * during wakeup. Wait until the CPU is quiescent.
+ * during wakeup. Wait until the CPU is quiescent. On RT kernels this also
+ * waits for pinned non-runnable tasks to leave the migrate disabled
+ * section.
*/
static void balance_hotplug_wait(void)
{
struct rq *rq = this_rq();
- rcuwait_wait_event(&rq->hotplug_wait, rq->nr_running == 1,
+ rcuwait_wait_event(&rq->hotplug_wait,
+ rq->nr_running == 1 && !rq_has_pinned_tasks(rq),
TASK_UNINTERRUPTIBLE);
}
@@ -7279,7 +7309,7 @@ int sched_cpu_dying(unsigned int cpu)
BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
set_rq_offline(rq);
}
- BUG_ON(rq->nr_running != 1);
+ BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq));
rq_unlock_irqrestore(rq, &rf);
calc_load_migrate(rq);
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1053,6 +1053,10 @@ struct rq {
/* Must be inspected within a rcu lock section */
struct cpuidle_state *idle_state;
#endif
+
+#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
+ unsigned int nr_pinned;
+#endif
};
#ifdef CONFIG_FAIR_GROUP_SCHED
prev parent reply other threads:[~2020-09-17 10:51 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-17 9:42 [patch 00/10] sched: Migrate disable support for RT Thomas Gleixner
2020-09-17 9:42 ` [patch 01/10] sched: Fix balance_callback() Thomas Gleixner
2020-09-17 9:42 ` [patch 02/10] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Thomas Gleixner
2020-09-17 9:42 ` [patch 03/10] sched/core: Wait for tasks being pushed away on hotplug Thomas Gleixner
2020-09-17 9:42 ` [patch 04/10] sched/hotplug: Consolidate task migration on CPU unplug Thomas Gleixner
2020-09-17 9:42 ` [patch 05/10] sched/core: Split __set_cpus_allowed_ptr() Thomas Gleixner
2020-09-17 9:42 ` [patch 06/10] sched: Add task components for migration control Thomas Gleixner
2020-09-17 9:42 ` [patch 07/10] sched/core: Add mechanism to wait for affinity setting to complete Thomas Gleixner
2020-09-17 9:42 ` [patch 08/10] sched: Add update_migratory() callback to scheduler classes Thomas Gleixner
2020-09-17 9:42 ` [patch 09/10] sched/core: Add migrate_disable/enable() Thomas Gleixner
2020-09-17 14:24 ` peterz
2020-09-17 14:38 ` Sebastian Siewior
2020-09-17 14:49 ` peterz
2020-09-17 15:13 ` Sebastian Siewior
2020-09-17 15:54 ` peterz
2020-09-17 16:30 ` Sebastian Siewior
2020-09-18 8:22 ` peterz
2020-09-18 8:48 ` Sebastian Siewior
2020-09-18 7:00 ` Thomas Gleixner
2020-09-18 8:28 ` peterz
2020-09-17 9:42 ` Thomas Gleixner [this message]
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