From: Peter Zijlstra <peterz@infradead.org>
To: tglx@linutronix.de, mingo@kernel.org
Cc: linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
qais.yousef@arm.com, swood@redhat.com, peterz@infradead.org,
valentin.schneider@arm.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, vincent.donnefort@arm.com
Subject: [PATCH 9/9] sched/core: Make migrate disable and CPU hotplug cooperative
Date: Mon, 21 Sep 2020 18:36:06 +0200 [thread overview]
Message-ID: <20200921163845.897527418@infradead.org> (raw)
In-Reply-To: 20200921163557.234036895@infradead.org
From: Thomas Gleixner <tglx@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.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/core.c | 36 ++++++++++++++++++++++++++++++------
kernel/sched/sched.h | 4 ++++
2 files changed, 34 insertions(+), 6 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1725,10 +1725,17 @@ static void migrate_disable_switch(struc
void migrate_disable(void)
{
- if (current->migration_disabled++)
+ struct task_struct *p = current;
+
+ if (p->migration_disabled) {
+ p->migration_disabled++;
return;
+ }
- barrier();
+ preempt_disable();
+ this_rq()->nr_pinned++;
+ p->migration_disabled = 1;
+ preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_disable);
@@ -1755,6 +1762,7 @@ void migrate_enable(void)
*/
barrier();
p->migration_disabled = 0;
+ this_rq()->nr_pinned--;
preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_enable);
@@ -1764,6 +1772,11 @@ static inline bool is_migration_disabled
return p->migration_disabled;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return rq->nr_pinned;
+}
+
#else
static inline void migrate_disable_switch(struct rq *rq, struct task_struct *p) { }
@@ -1773,6 +1786,11 @@ static inline bool is_migration_disabled
return false;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return false;
+}
+
#endif
/*
@@ -2809,7 +2827,8 @@ 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);
}
@@ -7009,15 +7028,20 @@ static bool balance_push(struct rq *rq)
* Both the cpu-hotplug and stop task are in this case and are
* required to complete the hotplug process.
*/
- if (is_per_cpu_kthread(push_task)) {
+ if (is_per_cpu_kthread(push_task) || is_migration_disabled(push_task)) {
/*
* If this is the idle task on the outgoing CPU try to wake
* up the hotplug control thread which might wait for the
* 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);
@@ -7290,7 +7314,7 @@ 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
next prev parent reply other threads:[~2020-09-21 16:39 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-21 16:35 [PATCH 0/9] sched: Migrate disable support Peter Zijlstra
2020-09-21 16:35 ` [PATCH 1/9] stop_machine: Add function and caller debug info Peter Zijlstra
2020-09-21 16:35 ` [PATCH 2/9] sched: Fix balance_callback() Peter Zijlstra
2020-09-23 14:08 ` Thomas Gleixner
2020-09-21 16:36 ` [PATCH 3/9] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Peter Zijlstra
2020-09-25 16:38 ` Dietmar Eggemann
2020-10-02 14:20 ` Peter Zijlstra
2020-09-21 16:36 ` [PATCH 4/9] sched/core: Wait for tasks being pushed away on hotplug Peter Zijlstra
2020-09-21 16:36 ` [PATCH 5/9] sched/hotplug: Consolidate task migration on CPU unplug Peter Zijlstra
2020-10-01 17:12 ` Vincent Donnefort
2020-10-02 14:17 ` Peter Zijlstra
2020-09-21 16:36 ` [PATCH 6/9] sched: Massage set_cpus_allowed Peter Zijlstra
2020-09-23 14:07 ` Thomas Gleixner
2020-09-21 16:36 ` [PATCH 7/9] sched: Add migrate_disable() Peter Zijlstra
2020-09-21 19:16 ` Thomas Gleixner
2020-09-21 20:42 ` Daniel Bristot de Oliveira
2020-09-23 8:31 ` Thomas Gleixner
2020-09-23 10:51 ` Daniel Bristot de Oliveira
2020-09-23 17:08 ` peterz
2020-09-23 17:54 ` Daniel Bristot de Oliveira
2020-09-23 7:48 ` peterz
2020-09-24 11:53 ` Valentin Schneider
2020-09-24 12:29 ` Peter Zijlstra
2020-09-24 12:33 ` Valentin Schneider
2020-09-24 12:35 ` Peter Zijlstra
2020-09-25 16:50 ` Sebastian Andrzej Siewior
2020-10-02 14:21 ` Peter Zijlstra
2020-10-02 14:36 ` Sebastian Andrzej Siewior
2020-09-21 16:36 ` [PATCH 8/9] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() Peter Zijlstra
2020-09-24 19:59 ` Valentin Schneider
2020-09-25 8:43 ` Peter Zijlstra
2020-09-25 10:07 ` Valentin Schneider
2020-09-25 9:05 ` Peter Zijlstra
2020-09-25 9:56 ` Peter Zijlstra
2020-09-25 10:09 ` Valentin Schneider
2020-09-21 16:36 ` Peter Zijlstra [this message]
2020-09-25 9:12 ` [PATCH 0/9] sched: Migrate disable support Dietmar Eggemann
2020-09-25 10:10 ` Peter Zijlstra
2020-09-25 11:58 ` Dietmar Eggemann
2020-09-25 12:19 ` Valentin Schneider
2020-09-25 17:49 ` Valentin Schneider
2020-09-29 9:15 ` Dietmar Eggemann
2020-09-25 18:17 ` Sebastian Andrzej Siewior
2020-09-25 19:32 ` Valentin Schneider
2020-10-02 14:30 ` Peter Zijlstra
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