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|
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
* Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
* Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner
*
* No idle tick implementation for low and high resolution timers
*
* Started by: Thomas Gleixner and Ingo Molnar
*/
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>
#include <linux/percpu.h>
#include <linux/nmi.h>
#include <linux/profile.h>
#include <linux/sched/signal.h>
#include <linux/sched/clock.h>
#include <linux/sched/stat.h>
#include <linux/sched/nohz.h>
#include <linux/sched/loadavg.h>
#include <linux/module.h>
#include <linux/irq_work.h>
#include <linux/posix-timers.h>
#include <linux/context_tracking.h>
#include <linux/mm.h>
#include <asm/irq_regs.h>
#include "tick-internal.h"
#include <trace/events/timer.h>
/*
* Per-CPU nohz control structure
*/
static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
struct tick_sched *tick_get_tick_sched(int cpu)
{
return &per_cpu(tick_cpu_sched, cpu);
}
#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
/*
* The time, when the last jiffy update happened. Write access must hold
* jiffies_lock and jiffies_seq. tick_nohz_next_event() needs to get a
* consistent view of jiffies and last_jiffies_update.
*/
static ktime_t last_jiffies_update;
/*
* Must be called with interrupts disabled !
*/
static void tick_do_update_jiffies64(ktime_t now)
{
unsigned long ticks = 1;
ktime_t delta, nextp;
/*
* 64bit can do a quick check without holding jiffies lock and
* without looking at the sequence count. The smp_load_acquire()
* pairs with the update done later in this function.
*
* 32bit cannot do that because the store of tick_next_period
* consists of two 32bit stores and the first store could move it
* to a random point in the future.
*/
if (IS_ENABLED(CONFIG_64BIT)) {
if (ktime_before(now, smp_load_acquire(&tick_next_period)))
return;
} else {
unsigned int seq;
/*
* Avoid contention on jiffies_lock and protect the quick
* check with the sequence count.
*/
do {
seq = read_seqcount_begin(&jiffies_seq);
nextp = tick_next_period;
} while (read_seqcount_retry(&jiffies_seq, seq));
if (ktime_before(now, nextp))
return;
}
/* Quick check failed, i.e. update is required. */
raw_spin_lock(&jiffies_lock);
/*
* Reevaluate with the lock held. Another CPU might have done the
* update already.
*/
if (ktime_before(now, tick_next_period)) {
raw_spin_unlock(&jiffies_lock);
return;
}
write_seqcount_begin(&jiffies_seq);
delta = ktime_sub(now, tick_next_period);
if (unlikely(delta >= TICK_NSEC)) {
/* Slow path for long idle sleep times */
s64 incr = TICK_NSEC;
ticks += ktime_divns(delta, incr);
last_jiffies_update = ktime_add_ns(last_jiffies_update,
incr * ticks);
} else {
last_jiffies_update = ktime_add_ns(last_jiffies_update,
TICK_NSEC);
}
/* Advance jiffies to complete the jiffies_seq protected job */
jiffies_64 += ticks;
/*
* Keep the tick_next_period variable up to date.
*/
nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC);
if (IS_ENABLED(CONFIG_64BIT)) {
/*
* Pairs with smp_load_acquire() in the lockless quick
* check above and ensures that the update to jiffies_64 is
* not reordered vs. the store to tick_next_period, neither
* by the compiler nor by the CPU.
*/
smp_store_release(&tick_next_period, nextp);
} else {
/*
* A plain store is good enough on 32bit as the quick check
* above is protected by the sequence count.
*/
tick_next_period = nextp;
}
/*
* Release the sequence count. calc_global_load() below is not
* protected by it, but jiffies_lock needs to be held to prevent
* concurrent invocations.
*/
write_seqcount_end(&jiffies_seq);
calc_global_load();
raw_spin_unlock(&jiffies_lock);
update_wall_time();
}
/*
* Initialize and return retrieve the jiffies update.
*/
static ktime_t tick_init_jiffy_update(void)
{
ktime_t period;
raw_spin_lock(&jiffies_lock);
write_seqcount_begin(&jiffies_seq);
/* Did we start the jiffies update yet ? */
if (last_jiffies_update == 0)
last_jiffies_update = tick_next_period;
period = last_jiffies_update;
write_seqcount_end(&jiffies_seq);
raw_spin_unlock(&jiffies_lock);
return period;
}
static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
{
int cpu = smp_processor_id();
#ifdef CONFIG_NO_HZ_COMMON
/*
* Check if the do_timer duty was dropped. We don't care about
* concurrency: This happens only when the CPU in charge went
* into a long sleep. If two CPUs happen to assign themselves to
* this duty, then the jiffies update is still serialized by
* jiffies_lock.
*
* If nohz_full is enabled, this should not happen because the
* tick_do_timer_cpu never relinquishes.
*/
if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) {
#ifdef CONFIG_NO_HZ_FULL
WARN_ON(tick_nohz_full_running);
#endif
tick_do_timer_cpu = cpu;
}
#endif
/* Check, if the jiffies need an update */
if (tick_do_timer_cpu == cpu)
tick_do_update_jiffies64(now);
if (ts->inidle)
ts->got_idle_tick = 1;
}
static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
{
#ifdef CONFIG_NO_HZ_COMMON
/*
* When we are idle and the tick is stopped, we have to touch
* the watchdog as we might not schedule for a really long
* time. This happens on complete idle SMP systems while
* waiting on the login prompt. We also increment the "start of
* idle" jiffy stamp so the idle accounting adjustment we do
* when we go busy again does not account too much ticks.
*/
if (ts->tick_stopped) {
touch_softlockup_watchdog_sched();
if (is_idle_task(current))
ts->idle_jiffies++;
/*
* In case the current tick fired too early past its expected
* expiration, make sure we don't bypass the next clock reprogramming
* to the same deadline.
*/
ts->next_tick = 0;
}
#endif
update_process_times(user_mode(regs));
profile_tick(CPU_PROFILING);
}
#endif
#ifdef CONFIG_NO_HZ_FULL
cpumask_var_t tick_nohz_full_mask;
bool tick_nohz_full_running;
EXPORT_SYMBOL_GPL(tick_nohz_full_running);
static atomic_t tick_dep_mask;
static bool check_tick_dependency(atomic_t *dep)
{
int val = atomic_read(dep);
if (val & TICK_DEP_MASK_POSIX_TIMER) {
trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
return true;
}
if (val & TICK_DEP_MASK_PERF_EVENTS) {
trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
return true;
}
if (val & TICK_DEP_MASK_SCHED) {
trace_tick_stop(0, TICK_DEP_MASK_SCHED);
return true;
}
if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
return true;
}
if (val & TICK_DEP_MASK_RCU) {
trace_tick_stop(0, TICK_DEP_MASK_RCU);
return true;
}
return false;
}
static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
{
lockdep_assert_irqs_disabled();
if (unlikely(!cpu_online(cpu)))
return false;
if (check_tick_dependency(&tick_dep_mask))
return false;
if (check_tick_dependency(&ts->tick_dep_mask))
return false;
if (check_tick_dependency(¤t->tick_dep_mask))
return false;
if (check_tick_dependency(¤t->signal->tick_dep_mask))
return false;
return true;
}
static void nohz_full_kick_func(struct irq_work *work)
{
/* Empty, the tick restart happens on tick_nohz_irq_exit() */
}
static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) =
IRQ_WORK_INIT_HARD(nohz_full_kick_func);
/*
* Kick this CPU if it's full dynticks in order to force it to
* re-evaluate its dependency on the tick and restart it if necessary.
* This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
* is NMI safe.
*/
static void tick_nohz_full_kick(void)
{
if (!tick_nohz_full_cpu(smp_processor_id()))
return;
irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
}
/*
* Kick the CPU if it's full dynticks in order to force it to
* re-evaluate its dependency on the tick and restart it if necessary.
*/
void tick_nohz_full_kick_cpu(int cpu)
{
if (!tick_nohz_full_cpu(cpu))
return;
irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
}
/*
* Kick all full dynticks CPUs in order to force these to re-evaluate
* their dependency on the tick and restart it if necessary.
*/
static void tick_nohz_full_kick_all(void)
{
int cpu;
if (!tick_nohz_full_running)
return;
preempt_disable();
for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
tick_nohz_full_kick_cpu(cpu);
preempt_enable();
}
static void tick_nohz_dep_set_all(atomic_t *dep,
enum tick_dep_bits bit)
{
int prev;
prev = atomic_fetch_or(BIT(bit), dep);
if (!prev)
tick_nohz_full_kick_all();
}
/*
* Set a global tick dependency. Used by perf events that rely on freq and
* by unstable clock.
*/
void tick_nohz_dep_set(enum tick_dep_bits bit)
{
tick_nohz_dep_set_all(&tick_dep_mask, bit);
}
void tick_nohz_dep_clear(enum tick_dep_bits bit)
{
atomic_andnot(BIT(bit), &tick_dep_mask);
}
/*
* Set per-CPU tick dependency. Used by scheduler and perf events in order to
* manage events throttling.
*/
void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
{
int prev;
struct tick_sched *ts;
ts = per_cpu_ptr(&tick_cpu_sched, cpu);
prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
if (!prev) {
preempt_disable();
/* Perf needs local kick that is NMI safe */
if (cpu == smp_processor_id()) {
tick_nohz_full_kick();
} else {
/* Remote irq work not NMI-safe */
if (!WARN_ON_ONCE(in_nmi()))
tick_nohz_full_kick_cpu(cpu);
}
preempt_enable();
}
}
EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);
void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
{
struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
atomic_andnot(BIT(bit), &ts->tick_dep_mask);
}
EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);
/*
* Set a per-task tick dependency. RCU need this. Also posix CPU timers
* in order to elapse per task timers.
*/
void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
{
if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask)) {
if (tsk == current) {
preempt_disable();
tick_nohz_full_kick();
preempt_enable();
} else {
/*
* Some future tick_nohz_full_kick_task()
* should optimize this.
*/
tick_nohz_full_kick_all();
}
}
}
EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task);
void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
{
atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
}
EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_task);
/*
* Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
* per process timers.
*/
void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
{
tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
}
void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
{
atomic_andnot(BIT(bit), &sig->tick_dep_mask);
}
/*
* Re-evaluate the need for the tick as we switch the current task.
* It might need the tick due to per task/process properties:
* perf events, posix CPU timers, ...
*/
void __tick_nohz_task_switch(void)
{
unsigned long flags;
struct tick_sched *ts;
local_irq_save(flags);
if (!tick_nohz_full_cpu(smp_processor_id()))
goto out;
ts = this_cpu_ptr(&tick_cpu_sched);
if (ts->tick_stopped) {
if (atomic_read(¤t->tick_dep_mask) ||
atomic_read(¤t->signal->tick_dep_mask))
tick_nohz_full_kick();
}
out:
local_irq_restore(flags);
}
/* Get the boot-time nohz CPU list from the kernel parameters. */
void __init tick_nohz_full_setup(cpumask_var_t cpumask)
{
alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
cpumask_copy(tick_nohz_full_mask, cpumask);
tick_nohz_full_running = true;
}
EXPORT_SYMBOL_GPL(tick_nohz_full_setup);
static int tick_nohz_cpu_down(unsigned int cpu)
{
/*
* The tick_do_timer_cpu CPU handles housekeeping duty (unbound
* timers, workqueues, timekeeping, ...) on behalf of full dynticks
* CPUs. It must remain online when nohz full is enabled.
*/
if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
return -EBUSY;
return 0;
}
void __init tick_nohz_init(void)
{
int cpu, ret;
if (!tick_nohz_full_running)
return;
/*
* Full dynticks uses irq work to drive the tick rescheduling on safe
* locking contexts. But then we need irq work to raise its own
* interrupts to avoid circular dependency on the tick
*/
if (!arch_irq_work_has_interrupt()) {
pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
cpumask_clear(tick_nohz_full_mask);
tick_nohz_full_running = false;
return;
}
if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) &&
!IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) {
cpu = smp_processor_id();
if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
pr_warn("NO_HZ: Clearing %d from nohz_full range "
"for timekeeping\n", cpu);
cpumask_clear_cpu(cpu, tick_nohz_full_mask);
}
}
for_each_cpu(cpu, tick_nohz_full_mask)
context_tracking_cpu_set(cpu);
ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
"kernel/nohz:predown", NULL,
tick_nohz_cpu_down);
WARN_ON(ret < 0);
pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
cpumask_pr_args(tick_nohz_full_mask));
}
#endif
/*
* NOHZ - aka dynamic tick functionality
*/
#ifdef CONFIG_NO_HZ_COMMON
/*
* NO HZ enabled ?
*/
bool tick_nohz_enabled __read_mostly = true;
unsigned long tick_nohz_active __read_mostly;
/*
* Enable / Disable tickless mode
*/
static int __init setup_tick_nohz(char *str)
{
return (kstrtobool(str, &tick_nohz_enabled) == 0);
}
__setup("nohz=", setup_tick_nohz);
bool tick_nohz_tick_stopped(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
return ts->tick_stopped;
}
bool tick_nohz_tick_stopped_cpu(int cpu)
{
struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
return ts->tick_stopped;
}
/**
* tick_nohz_update_jiffies - update jiffies when idle was interrupted
*
* Called from interrupt entry when the CPU was idle
*
* In case the sched_tick was stopped on this CPU, we have to check if jiffies
* must be updated. Otherwise an interrupt handler could use a stale jiffy
* value. We do this unconditionally on any CPU, as we don't know whether the
* CPU, which has the update task assigned is in a long sleep.
*/
static void tick_nohz_update_jiffies(ktime_t now)
{
unsigned long flags;
__this_cpu_write(tick_cpu_sched.idle_waketime, now);
local_irq_save(flags);
tick_do_update_jiffies64(now);
local_irq_restore(flags);
touch_softlockup_watchdog_sched();
}
/*
* Updates the per-CPU time idle statistics counters
*/
static void
update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
{
ktime_t delta;
if (ts->idle_active) {
delta = ktime_sub(now, ts->idle_entrytime);
if (nr_iowait_cpu(cpu) > 0)
ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
else
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
ts->idle_entrytime = now;
}
if (last_update_time)
*last_update_time = ktime_to_us(now);
}
static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
{
update_ts_time_stats(smp_processor_id(), ts, now, NULL);
ts->idle_active = 0;
sched_clock_idle_wakeup_event();
}
static void tick_nohz_start_idle(struct tick_sched *ts)
{
ts->idle_entrytime = ktime_get();
ts->idle_active = 1;
sched_clock_idle_sleep_event();
}
/**
* get_cpu_idle_time_us - get the total idle time of a CPU
* @cpu: CPU number to query
* @last_update_time: variable to store update time in. Do not update
* counters if NULL.
*
* Return the cumulative idle time (since boot) for a given
* CPU, in microseconds.
*
* This time is measured via accounting rather than sampling,
* and is as accurate as ktime_get() is.
*
* This function returns -1 if NOHZ is not enabled.
*/
u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
ktime_t now, idle;
if (!tick_nohz_active)
return -1;
now = ktime_get();
if (last_update_time) {
update_ts_time_stats(cpu, ts, now, last_update_time);
idle = ts->idle_sleeptime;
} else {
if (ts->idle_active && !nr_iowait_cpu(cpu)) {
ktime_t delta = ktime_sub(now, ts->idle_entrytime);
idle = ktime_add(ts->idle_sleeptime, delta);
} else {
idle = ts->idle_sleeptime;
}
}
return ktime_to_us(idle);
}
EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
/**
* get_cpu_iowait_time_us - get the total iowait time of a CPU
* @cpu: CPU number to query
* @last_update_time: variable to store update time in. Do not update
* counters if NULL.
*
* Return the cumulative iowait time (since boot) for a given
* CPU, in microseconds.
*
* This time is measured via accounting rather than sampling,
* and is as accurate as ktime_get() is.
*
* This function returns -1 if NOHZ is not enabled.
*/
u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
ktime_t now, iowait;
if (!tick_nohz_active)
return -1;
now = ktime_get();
if (last_update_time) {
update_ts_time_stats(cpu, ts, now, last_update_time);
iowait = ts->iowait_sleeptime;
} else {
if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
ktime_t delta = ktime_sub(now, ts->idle_entrytime);
iowait = ktime_add(ts->iowait_sleeptime, delta);
} else {
iowait = ts->iowait_sleeptime;
}
}
return ktime_to_us(iowait);
}
EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
{
hrtimer_cancel(&ts->sched_timer);
hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
/* Forward the time to expire in the future */
hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
hrtimer_start_expires(&ts->sched_timer,
HRTIMER_MODE_ABS_PINNED_HARD);
} else {
tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
}
/*
* Reset to make sure next tick stop doesn't get fooled by past
* cached clock deadline.
*/
ts->next_tick = 0;
}
static inline bool local_timer_softirq_pending(void)
{
return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
}
static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
{
u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
unsigned long basejiff;
unsigned int seq;
/* Read jiffies and the time when jiffies were updated last */
do {
seq = read_seqcount_begin(&jiffies_seq);
basemono = last_jiffies_update;
basejiff = jiffies;
} while (read_seqcount_retry(&jiffies_seq, seq));
ts->last_jiffies = basejiff;
ts->timer_expires_base = basemono;
/*
* Keep the periodic tick, when RCU, architecture or irq_work
* requests it.
* Aside of that check whether the local timer softirq is
* pending. If so its a bad idea to call get_next_timer_interrupt()
* because there is an already expired timer, so it will request
* immediate expiry, which rearms the hardware timer with a
* minimal delta which brings us back to this place
* immediately. Lather, rinse and repeat...
*/
if (rcu_needs_cpu(basemono, &next_rcu) || arch_needs_cpu() ||
irq_work_needs_cpu() || local_timer_softirq_pending()) {
next_tick = basemono + TICK_NSEC;
} else {
/*
* Get the next pending timer. If high resolution
* timers are enabled this only takes the timer wheel
* timers into account. If high resolution timers are
* disabled this also looks at the next expiring
* hrtimer.
*/
next_tmr = get_next_timer_interrupt(basejiff, basemono);
ts->next_timer = next_tmr;
/* Take the next rcu event into account */
next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
}
/*
* If the tick is due in the next period, keep it ticking or
* force prod the timer.
*/
delta = next_tick - basemono;
if (delta <= (u64)TICK_NSEC) {
/*
* Tell the timer code that the base is not idle, i.e. undo
* the effect of get_next_timer_interrupt():
*/
timer_clear_idle();
/*
* We've not stopped the tick yet, and there's a timer in the
* next period, so no point in stopping it either, bail.
*/
if (!ts->tick_stopped) {
ts->timer_expires = 0;
goto out;
}
}
/*
* If this CPU is the one which had the do_timer() duty last, we limit
* the sleep time to the timekeeping max_deferment value.
* Otherwise we can sleep as long as we want.
*/
delta = timekeeping_max_deferment();
if (cpu != tick_do_timer_cpu &&
(tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last))
delta = KTIME_MAX;
/* Calculate the next expiry time */
if (delta < (KTIME_MAX - basemono))
expires = basemono + delta;
else
expires = KTIME_MAX;
ts->timer_expires = min_t(u64, expires, next_tick);
out:
return ts->timer_expires;
}
static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
{
struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
u64 basemono = ts->timer_expires_base;
u64 expires = ts->timer_expires;
ktime_t tick = expires;
/* Make sure we won't be trying to stop it twice in a row. */
ts->timer_expires_base = 0;
/*
* If this CPU is the one which updates jiffies, then give up
* the assignment and let it be taken by the CPU which runs
* the tick timer next, which might be this CPU as well. If we
* don't drop this here the jiffies might be stale and
* do_timer() never invoked. Keep track of the fact that it
* was the one which had the do_timer() duty last.
*/
if (cpu == tick_do_timer_cpu) {
tick_do_timer_cpu = TICK_DO_TIMER_NONE;
ts->do_timer_last = 1;
} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
ts->do_timer_last = 0;
}
/* Skip reprogram of event if its not changed */
if (ts->tick_stopped && (expires == ts->next_tick)) {
/* Sanity check: make sure clockevent is actually programmed */
if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer))
return;
WARN_ON_ONCE(1);
printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n",
basemono, ts->next_tick, dev->next_event,
hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer));
}
/*
* nohz_stop_sched_tick can be called several times before
* the nohz_restart_sched_tick is called. This happens when
* interrupts arrive which do not cause a reschedule. In the
* first call we save the current tick time, so we can restart
* the scheduler tick in nohz_restart_sched_tick.
*/
if (!ts->tick_stopped) {
calc_load_nohz_start();
quiet_vmstat();
ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
ts->tick_stopped = 1;
trace_tick_stop(1, TICK_DEP_MASK_NONE);
}
ts->next_tick = tick;
/*
* If the expiration time == KTIME_MAX, then we simply stop
* the tick timer.
*/
if (unlikely(expires == KTIME_MAX)) {
if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
hrtimer_cancel(&ts->sched_timer);
return;
}
if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
hrtimer_start(&ts->sched_timer, tick,
HRTIMER_MODE_ABS_PINNED_HARD);
} else {
hrtimer_set_expires(&ts->sched_timer, tick);
tick_program_event(tick, 1);
}
}
static void tick_nohz_retain_tick(struct tick_sched *ts)
{
ts->timer_expires_base = 0;
}
#ifdef CONFIG_NO_HZ_FULL
static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu)
{
if (tick_nohz_next_event(ts, cpu))
tick_nohz_stop_tick(ts, cpu);
else
tick_nohz_retain_tick(ts);
}
#endif /* CONFIG_NO_HZ_FULL */
static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
{
/* Update jiffies first */
tick_do_update_jiffies64(now);
/*
* Clear the timer idle flag, so we avoid IPIs on remote queueing and
* the clock forward checks in the enqueue path:
*/
timer_clear_idle();
calc_load_nohz_stop();
touch_softlockup_watchdog_sched();
/*
* Cancel the scheduled timer and restore the tick
*/
ts->tick_stopped = 0;
tick_nohz_restart(ts, now);
}
static void __tick_nohz_full_update_tick(struct tick_sched *ts,
ktime_t now)
{
#ifdef CONFIG_NO_HZ_FULL
int cpu = smp_processor_id();
if (can_stop_full_tick(cpu, ts))
tick_nohz_stop_sched_tick(ts, cpu);
else if (ts->tick_stopped)
tick_nohz_restart_sched_tick(ts, now);
#endif
}
static void tick_nohz_full_update_tick(struct tick_sched *ts)
{
if (!tick_nohz_full_cpu(smp_processor_id()))
return;
if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
return;
__tick_nohz_full_update_tick(ts, ktime_get());
}
static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
{
/*
* If this CPU is offline and it is the one which updates
* jiffies, then give up the assignment and let it be taken by
* the CPU which runs the tick timer next. If we don't drop
* this here the jiffies might be stale and do_timer() never
* invoked.
*/
if (unlikely(!cpu_online(cpu))) {
if (cpu == tick_do_timer_cpu)
tick_do_timer_cpu = TICK_DO_TIMER_NONE;
/*
* Make sure the CPU doesn't get fooled by obsolete tick
* deadline if it comes back online later.
*/
ts->next_tick = 0;
return false;
}
if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
return false;
if (need_resched())
return false;
if (unlikely(local_softirq_pending())) {
static int ratelimit;
if (ratelimit < 10 && !local_bh_blocked() &&
(local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x!!!\n",
(unsigned int) local_softirq_pending());
ratelimit++;
}
return false;
}
if (tick_nohz_full_enabled()) {
/*
* Keep the tick alive to guarantee timekeeping progression
* if there are full dynticks CPUs around
*/
if (tick_do_timer_cpu == cpu)
return false;
/* Should not happen for nohz-full */
if (WARN_ON_ONCE(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
return false;
}
return true;
}
static void __tick_nohz_idle_stop_tick(struct tick_sched *ts)
{
ktime_t expires;
int cpu = smp_processor_id();
/*
* If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
* tick timer expiration time is known already.
*/
if (ts->timer_expires_base)
expires = ts->timer_expires;
else if (can_stop_idle_tick(cpu, ts))
expires = tick_nohz_next_event(ts, cpu);
else
return;
ts->idle_calls++;
if (expires > 0LL) {
int was_stopped = ts->tick_stopped;
tick_nohz_stop_tick(ts, cpu);
ts->idle_sleeps++;
ts->idle_expires = expires;
if (!was_stopped && ts->tick_stopped) {
ts->idle_jiffies = ts->last_jiffies;
nohz_balance_enter_idle(cpu);
}
} else {
tick_nohz_retain_tick(ts);
}
}
/**
* tick_nohz_idle_stop_tick - stop the idle tick from the idle task
*
* When the next event is more than a tick into the future, stop the idle tick
*/
void tick_nohz_idle_stop_tick(void)
{
__tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched));
}
void tick_nohz_idle_retain_tick(void)
{
tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
/*
* Undo the effect of get_next_timer_interrupt() called from
* tick_nohz_next_event().
*/
timer_clear_idle();
}
/**
* tick_nohz_idle_enter - prepare for entering idle on the current CPU
*
* Called when we start the idle loop.
*/
void tick_nohz_idle_enter(void)
{
struct tick_sched *ts;
lockdep_assert_irqs_enabled();
local_irq_disable();
ts = this_cpu_ptr(&tick_cpu_sched);
WARN_ON_ONCE(ts->timer_expires_base);
ts->inidle = 1;
tick_nohz_start_idle(ts);
local_irq_enable();
}
/**
* tick_nohz_irq_exit - update next tick event from interrupt exit
*
* When an interrupt fires while we are idle and it doesn't cause
* a reschedule, it may still add, modify or delete a timer, enqueue
* an RCU callback, etc...
* So we need to re-calculate and reprogram the next tick event.
*/
void tick_nohz_irq_exit(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
if (ts->inidle)
tick_nohz_start_idle(ts);
else
tick_nohz_full_update_tick(ts);
}
/**
* tick_nohz_idle_got_tick - Check whether or not the tick handler has run
*/
bool tick_nohz_idle_got_tick(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
if (ts->got_idle_tick) {
ts->got_idle_tick = 0;
return true;
}
return false;
}
/**
* tick_nohz_get_next_hrtimer - return the next expiration time for the hrtimer
* or the tick, whatever that expires first. Note that, if the tick has been
* stopped, it returns the next hrtimer.
*
* Called from power state control code with interrupts disabled
*/
ktime_t tick_nohz_get_next_hrtimer(void)
{
return __this_cpu_read(tick_cpu_device.evtdev)->next_event;
}
/**
* tick_nohz_get_sleep_length - return the expected length of the current sleep
* @delta_next: duration until the next event if the tick cannot be stopped
*
* Called from power state control code with interrupts disabled.
*
* The return value of this function and/or the value returned by it through the
* @delta_next pointer can be negative which must be taken into account by its
* callers.
*/
ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
{
struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
int cpu = smp_processor_id();
/*
* The idle entry time is expected to be a sufficient approximation of
* the current time at this point.
*/
ktime_t now = ts->idle_entrytime;
ktime_t next_event;
WARN_ON_ONCE(!ts->inidle);
*delta_next = ktime_sub(dev->next_event, now);
if (!can_stop_idle_tick(cpu, ts))
return *delta_next;
next_event = tick_nohz_next_event(ts, cpu);
if (!next_event)
return *delta_next;
/*
* If the next highres timer to expire is earlier than next_event, the
* idle governor needs to know that.
*/
next_event = min_t(u64, next_event,
hrtimer_next_event_without(&ts->sched_timer));
return ktime_sub(next_event, now);
}
/**
* tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
* for a particular CPU.
*
* Called from the schedutil frequency scaling governor in scheduler context.
*/
unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
{
struct tick_sched *ts = tick_get_tick_sched(cpu);
return ts->idle_calls;
}
/**
* tick_nohz_get_idle_calls - return the current idle calls counter value
*
* Called from the schedutil frequency scaling governor in scheduler context.
*/
unsigned long tick_nohz_get_idle_calls(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
return ts->idle_calls;
}
static void tick_nohz_account_idle_time(struct tick_sched *ts,
ktime_t now)
{
unsigned long ticks;
ts->idle_exittime = now;
if (vtime_accounting_enabled_this_cpu())
return;
/*
* We stopped the tick in idle. Update process times would miss the
* time we slept as update_process_times does only a 1 tick
* accounting. Enforce that this is accounted to idle !
*/
ticks = jiffies - ts->idle_jiffies;
/*
* We might be one off. Do not randomly account a huge number of ticks!
*/
if (ticks && ticks < LONG_MAX)
account_idle_ticks(ticks);
}
void tick_nohz_idle_restart_tick(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
if (ts->tick_stopped) {
ktime_t now = ktime_get();
tick_nohz_restart_sched_tick(ts, now);
tick_nohz_account_idle_time(ts, now);
}
}
static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now)
{
if (tick_nohz_full_cpu(smp_processor_id()))
__tick_nohz_full_update_tick(ts, now);
else
tick_nohz_restart_sched_tick(ts, now);
tick_nohz_account_idle_time(ts, now);
}
/**
* tick_nohz_idle_exit - restart the idle tick from the idle task
*
* Restart the idle tick when the CPU is woken up from idle
* This also exit the RCU extended quiescent state. The CPU
* can use RCU again after this function is called.
*/
void tick_nohz_idle_exit(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
bool idle_active, tick_stopped;
ktime_t now;
local_irq_disable();
WARN_ON_ONCE(!ts->inidle);
WARN_ON_ONCE(ts->timer_expires_base);
ts->inidle = 0;
idle_active = ts->idle_active;
tick_stopped = ts->tick_stopped;
if (idle_active || tick_stopped)
now = ktime_get();
if (idle_active)
tick_nohz_stop_idle(ts, now);
if (tick_stopped)
tick_nohz_idle_update_tick(ts, now);
local_irq_enable();
}
/*
* The nohz low res interrupt handler
*/
static void tick_nohz_handler(struct clock_event_device *dev)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
struct pt_regs *regs = get_irq_regs();
ktime_t now = ktime_get();
dev->next_event = KTIME_MAX;
tick_sched_do_timer(ts, now);
tick_sched_handle(ts, regs);
/* No need to reprogram if we are running tickless */
if (unlikely(ts->tick_stopped))
return;
hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
}
static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
{
if (!tick_nohz_enabled)
return;
ts->nohz_mode = mode;
/* One update is enough */
if (!test_and_set_bit(0, &tick_nohz_active))
timers_update_nohz();
}
/**
* tick_nohz_switch_to_nohz - switch to nohz mode
*/
static void tick_nohz_switch_to_nohz(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
ktime_t next;
if (!tick_nohz_enabled)
return;
if (tick_switch_to_oneshot(tick_nohz_handler))
return;
/*
* Recycle the hrtimer in ts, so we can share the
* hrtimer_forward with the highres code.
*/
hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
/* Get the next period */
next = tick_init_jiffy_update();
hrtimer_set_expires(&ts->sched_timer, next);
hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
}
static inline void tick_nohz_irq_enter(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
ktime_t now;
if (!ts->idle_active && !ts->tick_stopped)
return;
now = ktime_get();
if (ts->idle_active)
tick_nohz_stop_idle(ts, now);
if (ts->tick_stopped)
tick_nohz_update_jiffies(now);
}
#else
static inline void tick_nohz_switch_to_nohz(void) { }
static inline void tick_nohz_irq_enter(void) { }
static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
#endif /* CONFIG_NO_HZ_COMMON */
/*
* Called from irq_enter to notify about the possible interruption of idle()
*/
void tick_irq_enter(void)
{
tick_check_oneshot_broadcast_this_cpu();
tick_nohz_irq_enter();
}
/*
* High resolution timer specific code
*/
#ifdef CONFIG_HIGH_RES_TIMERS
/*
* We rearm the timer until we get disabled by the idle code.
* Called with interrupts disabled.
*/
static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
{
struct tick_sched *ts =
container_of(timer, struct tick_sched, sched_timer);
struct pt_regs *regs = get_irq_regs();
ktime_t now = ktime_get();
tick_sched_do_timer(ts, now);
/*
* Do not call, when we are not in irq context and have
* no valid regs pointer
*/
if (regs)
tick_sched_handle(ts, regs);
else
ts->next_tick = 0;
/* No need to reprogram if we are in idle or full dynticks mode */
if (unlikely(ts->tick_stopped))
return HRTIMER_NORESTART;
hrtimer_forward(timer, now, TICK_NSEC);
return HRTIMER_RESTART;
}
static int sched_skew_tick;
static int __init skew_tick(char *str)
{
get_option(&str, &sched_skew_tick);
return 0;
}
early_param("skew_tick", skew_tick);
/**
* tick_setup_sched_timer - setup the tick emulation timer
*/
void tick_setup_sched_timer(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
ktime_t now = ktime_get();
/*
* Emulate tick processing via per-CPU hrtimers:
*/
hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
ts->sched_timer.function = tick_sched_timer;
/* Get the next period (per-CPU) */
hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
/* Offset the tick to avert jiffies_lock contention. */
if (sched_skew_tick) {
u64 offset = TICK_NSEC >> 1;
do_div(offset, num_possible_cpus());
offset *= smp_processor_id();
hrtimer_add_expires_ns(&ts->sched_timer, offset);
}
hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
}
#endif /* HIGH_RES_TIMERS */
#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
void tick_cancel_sched_timer(int cpu)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
# ifdef CONFIG_HIGH_RES_TIMERS
if (ts->sched_timer.base)
hrtimer_cancel(&ts->sched_timer);
# endif
memset(ts, 0, sizeof(*ts));
}
#endif
/**
* Async notification about clocksource changes
*/
void tick_clock_notify(void)
{
int cpu;
for_each_possible_cpu(cpu)
set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
}
/*
* Async notification about clock event changes
*/
void tick_oneshot_notify(void)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
set_bit(0, &ts->check_clocks);
}
/**
* Check, if a change happened, which makes oneshot possible.
*
* Called cyclic from the hrtimer softirq (driven by the timer
* softirq) allow_nohz signals, that we can switch into low-res nohz
* mode, because high resolution timers are disabled (either compile
* or runtime). Called with interrupts disabled.
*/
int tick_check_oneshot_change(int allow_nohz)
{
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
if (!test_and_clear_bit(0, &ts->check_clocks))
return 0;
if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
return 0;
if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
return 0;
if (!allow_nohz)
return 1;
tick_nohz_switch_to_nohz();
return 0;
}
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