summaryrefslogtreecommitdiffstats
path: root/kernel
diff options
context:
space:
mode:
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c57
1 files changed, 49 insertions, 8 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2b037f195473..0b22e55cebe8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3486,8 +3486,36 @@ void scheduler_tick(void)
struct tick_work {
int cpu;
+ atomic_t state;
struct delayed_work work;
};
+/* Values for ->state, see diagram below. */
+#define TICK_SCHED_REMOTE_OFFLINE 0
+#define TICK_SCHED_REMOTE_OFFLINING 1
+#define TICK_SCHED_REMOTE_RUNNING 2
+
+/*
+ * State diagram for ->state:
+ *
+ *
+ * TICK_SCHED_REMOTE_OFFLINE
+ * | ^
+ * | |
+ * | | sched_tick_remote()
+ * | |
+ * | |
+ * +--TICK_SCHED_REMOTE_OFFLINING
+ * | ^
+ * | |
+ * sched_tick_start() | | sched_tick_stop()
+ * | |
+ * V |
+ * TICK_SCHED_REMOTE_RUNNING
+ *
+ *
+ * Other transitions get WARN_ON_ONCE(), except that sched_tick_remote()
+ * and sched_tick_start() are happy to leave the state in RUNNING.
+ */
static struct tick_work __percpu *tick_work_cpu;
@@ -3500,6 +3528,7 @@ static void sched_tick_remote(struct work_struct *work)
struct task_struct *curr;
struct rq_flags rf;
u64 delta;
+ int os;
/*
* Handle the tick only if it appears the remote CPU is running in full
@@ -3513,7 +3542,7 @@ static void sched_tick_remote(struct work_struct *work)
rq_lock_irq(rq, &rf);
curr = rq->curr;
- if (is_idle_task(curr))
+ if (is_idle_task(curr) || cpu_is_offline(cpu))
goto out_unlock;
update_rq_clock(rq);
@@ -3533,13 +3562,18 @@ out_requeue:
/*
* Run the remote tick once per second (1Hz). This arbitrary
* frequency is large enough to avoid overload but short enough
- * to keep scheduler internal stats reasonably up to date.
+ * to keep scheduler internal stats reasonably up to date. But
+ * first update state to reflect hotplug activity if required.
*/
- queue_delayed_work(system_unbound_wq, dwork, HZ);
+ os = atomic_fetch_add_unless(&twork->state, -1, TICK_SCHED_REMOTE_RUNNING);
+ WARN_ON_ONCE(os == TICK_SCHED_REMOTE_OFFLINE);
+ if (os == TICK_SCHED_REMOTE_RUNNING)
+ queue_delayed_work(system_unbound_wq, dwork, HZ);
}
static void sched_tick_start(int cpu)
{
+ int os;
struct tick_work *twork;
if (housekeeping_cpu(cpu, HK_FLAG_TICK))
@@ -3548,15 +3582,20 @@ static void sched_tick_start(int cpu)
WARN_ON_ONCE(!tick_work_cpu);
twork = per_cpu_ptr(tick_work_cpu, cpu);
- twork->cpu = cpu;
- INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
- queue_delayed_work(system_unbound_wq, &twork->work, HZ);
+ os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_RUNNING);
+ WARN_ON_ONCE(os == TICK_SCHED_REMOTE_RUNNING);
+ if (os == TICK_SCHED_REMOTE_OFFLINE) {
+ twork->cpu = cpu;
+ INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
+ queue_delayed_work(system_unbound_wq, &twork->work, HZ);
+ }
}
#ifdef CONFIG_HOTPLUG_CPU
static void sched_tick_stop(int cpu)
{
struct tick_work *twork;
+ int os;
if (housekeeping_cpu(cpu, HK_FLAG_TICK))
return;
@@ -3564,7 +3603,10 @@ static void sched_tick_stop(int cpu)
WARN_ON_ONCE(!tick_work_cpu);
twork = per_cpu_ptr(tick_work_cpu, cpu);
- cancel_delayed_work_sync(&twork->work);
+ /* There cannot be competing actions, but don't rely on stop-machine. */
+ os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_OFFLINING);
+ WARN_ON_ONCE(os != TICK_SCHED_REMOTE_RUNNING);
+ /* Don't cancel, as this would mess up the state machine. */
}
#endif /* CONFIG_HOTPLUG_CPU */
@@ -3572,7 +3614,6 @@ int __init sched_tick_offload_init(void)
{
tick_work_cpu = alloc_percpu(struct tick_work);
BUG_ON(!tick_work_cpu);
-
return 0;
}