diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/core.c | 57 |
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; } |