drm/modes: Fix drm_mode_vrefres() docs

[drm/drm-misc.git] / kernel / sched / idle.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Generic entry points for the idle threads and
 * implementation of the idle task scheduling class.
 *
 * (NOTE: these are not related to SCHED_IDLE batch scheduled
 *        tasks which are handled in sched/fair.c )
 */

/* Linker adds these: start and end of __cpuidle functions */
extern char __cpuidle_text_start[], __cpuidle_text_end[];

/**
 * sched_idle_set_state - Record idle state for the current CPU.
 * @idle_state: State to record.
 */
void sched_idle_set_state(struct cpuidle_state *idle_state)
{
        idle_set_state(this_rq(), idle_state);
}

static int __read_mostly cpu_idle_force_poll;

void cpu_idle_poll_ctrl(bool enable)
{
        if (enable) {
                cpu_idle_force_poll++;
        } else {
                cpu_idle_force_poll--;
                WARN_ON_ONCE(cpu_idle_force_poll < 0);
        }
}

#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
static int __init cpu_idle_poll_setup(char *__unused)
{
        cpu_idle_force_poll = 1;

        return 1;
}
__setup("nohlt", cpu_idle_poll_setup);

static int __init cpu_idle_nopoll_setup(char *__unused)
{
        cpu_idle_force_poll = 0;

        return 1;
}
__setup("hlt", cpu_idle_nopoll_setup);
#endif

static noinline int __cpuidle cpu_idle_poll(void)
{
        instrumentation_begin();
        trace_cpu_idle(0, smp_processor_id());
        stop_critical_timings();
        ct_cpuidle_enter();

        raw_local_irq_enable();
        while (!tif_need_resched() &&
               (cpu_idle_force_poll || tick_check_broadcast_expired()))
                cpu_relax();
        raw_local_irq_disable();

        ct_cpuidle_exit();
        start_critical_timings();
        trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
        local_irq_enable();
        instrumentation_end();

        return 1;
}

/* Weak implementations for optional arch specific functions */
void __weak arch_cpu_idle_prepare(void) { }
void __weak arch_cpu_idle_enter(void) { }
void __weak arch_cpu_idle_exit(void) { }
void __weak __noreturn arch_cpu_idle_dead(void) { while (1); }
void __weak arch_cpu_idle(void)
{
        cpu_idle_force_poll = 1;
}

#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE
DEFINE_STATIC_KEY_FALSE(arch_needs_tick_broadcast);

static inline void cond_tick_broadcast_enter(void)
{
        if (static_branch_unlikely(&arch_needs_tick_broadcast))
                tick_broadcast_enter();
}

static inline void cond_tick_broadcast_exit(void)
{
        if (static_branch_unlikely(&arch_needs_tick_broadcast))
                tick_broadcast_exit();
}
#else
static inline void cond_tick_broadcast_enter(void) { }
static inline void cond_tick_broadcast_exit(void) { }
#endif

/**
 * default_idle_call - Default CPU idle routine.
 *
 * To use when the cpuidle framework cannot be used.
 */
void __cpuidle default_idle_call(void)
{
        instrumentation_begin();
        if (!current_clr_polling_and_test()) {
                cond_tick_broadcast_enter();
                trace_cpu_idle(1, smp_processor_id());
                stop_critical_timings();

                ct_cpuidle_enter();
                arch_cpu_idle();
                ct_cpuidle_exit();

                start_critical_timings();
                trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
                cond_tick_broadcast_exit();
        }
        local_irq_enable();
        instrumentation_end();
}

static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
                               struct cpuidle_device *dev)
{
        if (current_clr_polling_and_test())
                return -EBUSY;

        return cpuidle_enter_s2idle(drv, dev);
}

static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
                      int next_state)
{
        /*
         * The idle task must be scheduled, it is pointless to go to idle, just
         * update no idle residency and return.
         */
        if (current_clr_polling_and_test()) {
                dev->last_residency_ns = 0;
                local_irq_enable();
                return -EBUSY;
        }

        /*
         * Enter the idle state previously returned by the governor decision.
         * This function will block until an interrupt occurs and will take
         * care of re-enabling the local interrupts
         */
        return cpuidle_enter(drv, dev, next_state);
}

/**
 * cpuidle_idle_call - the main idle function
 *
 * NOTE: no locks or semaphores should be used here
 *
 * On architectures that support TIF_POLLING_NRFLAG, is called with polling
 * set, and it returns with polling set.  If it ever stops polling, it
 * must clear the polling bit.
 */
static void cpuidle_idle_call(void)
{
        struct cpuidle_device *dev = cpuidle_get_device();
        struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
        int next_state, entered_state;

        /*
         * Check if the idle task must be rescheduled. If it is the
         * case, exit the function after re-enabling the local IRQ.
         */
        if (need_resched()) {
                local_irq_enable();
                return;
        }

        if (cpuidle_not_available(drv, dev)) {
                tick_nohz_idle_stop_tick();

                default_idle_call();
                goto exit_idle;
        }

        /*
         * Suspend-to-idle ("s2idle") is a system state in which all user space
         * has been frozen, all I/O devices have been suspended and the only
         * activity happens here and in interrupts (if any). In that case bypass
         * the cpuidle governor and go straight for the deepest idle state
         * available.  Possibly also suspend the local tick and the entire
         * timekeeping to prevent timer interrupts from kicking us out of idle
         * until a proper wakeup interrupt happens.
         */

        if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
                u64 max_latency_ns;

                if (idle_should_enter_s2idle()) {

                        entered_state = call_cpuidle_s2idle(drv, dev);
                        if (entered_state > 0)
                                goto exit_idle;

                        max_latency_ns = U64_MAX;
                } else {
                        max_latency_ns = dev->forced_idle_latency_limit_ns;
                }

                tick_nohz_idle_stop_tick();

                next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
                call_cpuidle(drv, dev, next_state);
        } else {
                bool stop_tick = true;

                /*
                 * Ask the cpuidle framework to choose a convenient idle state.
                 */
                next_state = cpuidle_select(drv, dev, &stop_tick);

                if (stop_tick || tick_nohz_tick_stopped())
                        tick_nohz_idle_stop_tick();
                else
                        tick_nohz_idle_retain_tick();

                entered_state = call_cpuidle(drv, dev, next_state);
                /*
                 * Give the governor an opportunity to reflect on the outcome
                 */
                cpuidle_reflect(dev, entered_state);
        }

exit_idle:
        __current_set_polling();

        /*
         * It is up to the idle functions to re-enable local interrupts
         */
        if (WARN_ON_ONCE(irqs_disabled()))
                local_irq_enable();
}

/*
 * Generic idle loop implementation
 *
 * Called with polling cleared.
 */
static void do_idle(void)
{
        int cpu = smp_processor_id();

        /*
         * Check if we need to update blocked load
         */
        nohz_run_idle_balance(cpu);

        /*
         * If the arch has a polling bit, we maintain an invariant:
         *
         * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
         * rq->idle). This means that, if rq->idle has the polling bit set,
         * then setting need_resched is guaranteed to cause the CPU to
         * reschedule.
         */

        __current_set_polling();
        tick_nohz_idle_enter();

        while (!need_resched()) {

                /*
                 * Interrupts shouldn't be re-enabled from that point on until
                 * the CPU sleeping instruction is reached. Otherwise an interrupt
                 * may fire and queue a timer that would be ignored until the CPU
                 * wakes from the sleeping instruction. And testing need_resched()
                 * doesn't tell about pending needed timer reprogram.
                 *
                 * Several cases to consider:
                 *
                 * - SLEEP-UNTIL-PENDING-INTERRUPT based instructions such as
                 *   "wfi" or "mwait" are fine because they can be entered with
                 *   interrupt disabled.
                 *
                 * - sti;mwait() couple is fine because the interrupts are
                 *   re-enabled only upon the execution of mwait, leaving no gap
                 *   in-between.
                 *
                 * - ROLLBACK based idle handlers with the sleeping instruction
                 *   called with interrupts enabled are NOT fine. In this scheme
                 *   when the interrupt detects it has interrupted an idle handler,
                 *   it rolls back to its beginning which performs the
                 *   need_resched() check before re-executing the sleeping
                 *   instruction. This can leak a pending needed timer reprogram.
                 *   If such a scheme is really mandatory due to the lack of an
                 *   appropriate CPU sleeping instruction, then a FAST-FORWARD
                 *   must instead be applied: when the interrupt detects it has
                 *   interrupted an idle handler, it must resume to the end of
                 *   this idle handler so that the generic idle loop is iterated
                 *   again to reprogram the tick.
                 */
                local_irq_disable();

                if (cpu_is_offline(cpu)) {
                        cpuhp_report_idle_dead();
                        arch_cpu_idle_dead();
                }

                arch_cpu_idle_enter();
                rcu_nocb_flush_deferred_wakeup();

                /*
                 * In poll mode we re-enable interrupts and spin. Also if we
                 * detected in the wakeup from idle path that the tick
                 * broadcast device expired for us, we don't want to go deep
                 * idle as we know that the IPI is going to arrive right away.
                 */
                if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
                        tick_nohz_idle_restart_tick();
                        cpu_idle_poll();
                } else {
                        cpuidle_idle_call();
                }
                arch_cpu_idle_exit();
        }

        /*
         * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
         * be set, propagate it into PREEMPT_NEED_RESCHED.
         *
         * This is required because for polling idle loops we will not have had
         * an IPI to fold the state for us.
         */
        preempt_set_need_resched();
        tick_nohz_idle_exit();
        __current_clr_polling();

        /*
         * We promise to call sched_ttwu_pending() and reschedule if
         * need_resched() is set while polling is set. That means that clearing
         * polling needs to be visible before doing these things.
         */
        smp_mb__after_atomic();

        /*
         * RCU relies on this call to be done outside of an RCU read-side
         * critical section.
         */
        flush_smp_call_function_queue();
        schedule_idle();

        if (unlikely(klp_patch_pending(current)))
                klp_update_patch_state(current);
}

bool cpu_in_idle(unsigned long pc)
{
        return pc >= (unsigned long)__cpuidle_text_start &&
                pc < (unsigned long)__cpuidle_text_end;
}

struct idle_timer {
        struct hrtimer timer;
        int done;
};

static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
{
        struct idle_timer *it = container_of(timer, struct idle_timer, timer);

        WRITE_ONCE(it->done, 1);
        set_tsk_need_resched(current);

        return HRTIMER_NORESTART;
}

void play_idle_precise(u64 duration_ns, u64 latency_ns)
{
        struct idle_timer it;

        /*
         * Only FIFO tasks can disable the tick since they don't need the forced
         * preemption.
         */
        WARN_ON_ONCE(current->policy != SCHED_FIFO);
        WARN_ON_ONCE(current->nr_cpus_allowed != 1);
        WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
        WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
        WARN_ON_ONCE(!duration_ns);
        WARN_ON_ONCE(current->mm);

        rcu_sleep_check();
        preempt_disable();
        current->flags |= PF_IDLE;
        cpuidle_use_deepest_state(latency_ns);

        it.done = 0;
        hrtimer_setup_on_stack(&it.timer, idle_inject_timer_fn, CLOCK_MONOTONIC,
                               HRTIMER_MODE_REL_HARD);
        hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
                      HRTIMER_MODE_REL_PINNED_HARD);

        while (!READ_ONCE(it.done))
                do_idle();

        cpuidle_use_deepest_state(0);
        current->flags &= ~PF_IDLE;

        preempt_fold_need_resched();
        preempt_enable();
}
EXPORT_SYMBOL_GPL(play_idle_precise);

void cpu_startup_entry(enum cpuhp_state state)
{
        current->flags |= PF_IDLE;
        arch_cpu_idle_prepare();
        cpuhp_online_idle(state);
        while (1)
                do_idle();
}

/*
 * idle-task scheduling class.
 */

#ifdef CONFIG_SMP
static int
select_task_rq_idle(struct task_struct *p, int cpu, int flags)
{
        return task_cpu(p); /* IDLE tasks as never migrated */
}

static int
balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
        return WARN_ON_ONCE(1);
}
#endif

/*
 * Idle tasks are unconditionally rescheduled:
 */
static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags)
{
        resched_curr(rq);
}

static void put_prev_task_idle(struct rq *rq, struct task_struct *prev, struct task_struct *next)
{
        dl_server_update_idle_time(rq, prev);
        scx_update_idle(rq, false);
}

static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
{
        update_idle_core(rq);
        scx_update_idle(rq, true);
        schedstat_inc(rq->sched_goidle);
        next->se.exec_start = rq_clock_task(rq);
}

struct task_struct *pick_task_idle(struct rq *rq)
{
        return rq->idle;
}

/*
 * It is not legal to sleep in the idle task - print a warning
 * message if some code attempts to do it:
 */
static bool
dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
{
        raw_spin_rq_unlock_irq(rq);
        printk(KERN_ERR "bad: scheduling from the idle thread!\n");
        dump_stack();
        raw_spin_rq_lock_irq(rq);
        return true;
}

/*
 * scheduler tick hitting a task of our scheduling class.
 *
 * NOTE: This function can be called remotely by the tick offload that
 * goes along full dynticks. Therefore no local assumption can be made
 * and everything must be accessed through the @rq and @curr passed in
 * parameters.
 */
static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
{
}

static void switched_to_idle(struct rq *rq, struct task_struct *p)
{
        BUG();
}

static void
prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
{
        BUG();
}

static void update_curr_idle(struct rq *rq)
{
}

/*
 * Simple, special scheduling class for the per-CPU idle tasks:
 */
DEFINE_SCHED_CLASS(idle) = {

        /* no enqueue/yield_task for idle tasks */

        /* dequeue is not valid, we print a debug message there: */
        .dequeue_task           = dequeue_task_idle,

        .wakeup_preempt         = wakeup_preempt_idle,

        .pick_task              = pick_task_idle,
        .put_prev_task          = put_prev_task_idle,
        .set_next_task          = set_next_task_idle,

#ifdef CONFIG_SMP
        .balance                = balance_idle,
        .select_task_rq         = select_task_rq_idle,
        .set_cpus_allowed       = set_cpus_allowed_common,
#endif

        .task_tick              = task_tick_idle,

        .prio_changed           = prio_changed_idle,
        .switched_to            = switched_to_idle,
        .update_curr            = update_curr_idle,
};