diff options
| -rw-r--r-- | include/linux/sched.h | 6 | ||||
| -rw-r--r-- | kernel/sched.c | 43 | ||||
| -rw-r--r-- | kernel/timer.c | 10 |
3 files changed, 58 insertions, 1 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index fed07d0..6a1e7af 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1541,6 +1541,12 @@ static inline void idle_task_exit(void) {} extern void sched_idle_next(void); +#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP) +extern void wake_up_idle_cpu(int cpu); +#else +static inline void wake_up_idle_cpu(int cpu) { } +#endif + #ifdef CONFIG_SCHED_DEBUG extern unsigned int sysctl_sched_latency; extern unsigned int sysctl_sched_min_granularity; diff --git a/kernel/sched.c b/kernel/sched.c index 28c73f0..8dcdec6 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1052,6 +1052,49 @@ static void resched_cpu(int cpu) resched_task(cpu_curr(cpu)); spin_unlock_irqrestore(&rq->lock, flags); } + +#ifdef CONFIG_NO_HZ +/* + * When add_timer_on() enqueues a timer into the timer wheel of an + * idle CPU then this timer might expire before the next timer event + * which is scheduled to wake up that CPU. In case of a completely + * idle system the next event might even be infinite time into the + * future. wake_up_idle_cpu() ensures that the CPU is woken up and + * leaves the inner idle loop so the newly added timer is taken into + * account when the CPU goes back to idle and evaluates the timer + * wheel for the next timer event. + */ +void wake_up_idle_cpu(int cpu) +{ + struct rq *rq = cpu_rq(cpu); + + if (cpu == smp_processor_id()) + return; + + /* + * This is safe, as this function is called with the timer + * wheel base lock of (cpu) held. When the CPU is on the way + * to idle and has not yet set rq->curr to idle then it will + * be serialized on the timer wheel base lock and take the new + * timer into account automatically. + */ + if (rq->curr != rq->idle) + return; + + /* + * We can set TIF_RESCHED on the idle task of the other CPU + * lockless. The worst case is that the other CPU runs the + * idle task through an additional NOOP schedule() + */ + set_tsk_thread_flag(rq->idle, TIF_NEED_RESCHED); + + /* NEED_RESCHED must be visible before we test polling */ + smp_mb(); + if (!tsk_is_polling(rq->idle)) + smp_send_reschedule(cpu); +} +#endif + #else static void __resched_task(struct task_struct *p, int tif_bit) { diff --git a/kernel/timer.c b/kernel/timer.c index 99b00a2..b024106 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -451,10 +451,18 @@ void add_timer_on(struct timer_list *timer, int cpu) spin_lock_irqsave(&base->lock, flags); timer_set_base(timer, base); internal_add_timer(base, timer); + /* + * Check whether the other CPU is idle and needs to be + * triggered to reevaluate the timer wheel when nohz is + * active. We are protected against the other CPU fiddling + * with the timer by holding the timer base lock. This also + * makes sure that a CPU on the way to idle can not evaluate + * the timer wheel. + */ + wake_up_idle_cpu(cpu); spin_unlock_irqrestore(&base->lock, flags); } - /** * mod_timer - modify a timer's timeout * @timer: the timer to be modified |