1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
|
From 02829fffd43c5fe3e617d07e0a94d5164324449b Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 23 Oct 2020 12:12:09 +0200
Subject: [PATCH 012/323] sched/core: Make migrate disable and CPU hotplug
cooperative
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
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>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/sched/core.c | 36 ++++++++++++++++++++++++++++++------
kernel/sched/sched.h | 4 ++++
2 files changed, 34 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3af7c42896c9..2517a003295b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1735,10 +1735,17 @@ static void migrate_disable_switch(struct rq *rq, struct task_struct *p)
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);
@@ -1765,6 +1772,7 @@ void migrate_enable(void)
*/
barrier();
p->migration_disabled = 0;
+ this_rq()->nr_pinned--;
preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_enable);
@@ -1774,6 +1782,11 @@ static inline bool is_migration_disabled(struct task_struct *p)
return p->migration_disabled;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return rq->nr_pinned;
+}
+
#endif
/*
@@ -2705,6 +2718,11 @@ static inline bool is_migration_disabled(struct task_struct *p)
return false;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return false;
+}
+
#endif
static void
@@ -7064,15 +7082,20 @@ static void 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);
@@ -7119,7 +7142,8 @@ 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);
}
@@ -7366,7 +7390,7 @@ int sched_cpu_dying(unsigned int cpu)
sched_tick_stop(cpu);
rq_lock_irqsave(rq, &rf);
- 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);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f3109adda484..8237c9ab2bb8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1057,6 +1057,10 @@ 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
--
2.43.0
|
