alistair23-linux/kernel/time/tick-sched.c
Frederic Weisbecker 2b17c545a4 nohz: Fix one jiffy count too far in idle cputime
When we stop the tick in idle, we save the current jiffies value
in ts->idle_jiffies. This snapshot is substracted from the later
value of jiffies when the tick is restarted and the resulting
delta is accounted as idle cputime. This is how we handle the
idle cputime accounting without the tick.

But sometimes we need to schedule the next tick to some time in
the future instead of completely stopping it. In this case, a
tick may happen before we restart the periodic behaviour and
from that tick we account one jiffy to idle cputime as usual but
we also increment the ts->idle_jiffies snapshot by one so that
when we compute the delta to account, we substract the one jiffy
we just accounted.

To prepare for stopping the tick outside idle, we introduced a
check that prevents from fixing up that ts->idle_jiffies if we
are not running the idle task. But we use idle_cpu() for that
and this is a problem if we run the tick while another CPU
remotely enqueues a ttwu to our runqueue:

CPU 0:                            CPU 1:

tick_sched_timer() {              ttwu_queue_remote()
       if (idle_cpu(CPU 0))
           ts->idle_jiffies++;
}

Here, idle_cpu() notes that &rq->wake_list is not empty and
hence won't consider the CPU as idle. As a result,
ts->idle_jiffies won't be incremented. But this is wrong because
we actually account the current jiffy to idle cputime. And that
jiffy won't get substracted from the nohz time delta. So in the
end, this jiffy is accounted twice.

Fix this by changing idle_cpu(smp_processor_id()) with
is_idle_task(current). This way the jiffy is substracted
correctly even if a ttwu operation is enqueued on the CPU.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org> # 3.5+
Link: http://lkml.kernel.org/r/1349308004-3482-1-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2012-10-05 10:22:20 +02:00

964 lines
24 KiB
C

/*
* linux/kernel/time/tick-sched.c
*
* 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
*
* Distribute under GPLv2.
*/
#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/profile.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <asm/irq_regs.h>
#include "tick-internal.h"
/*
* Per cpu nohz control structure
*/
static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
/*
* The time, when the last jiffy update happened. Protected by xtime_lock.
*/
static ktime_t last_jiffies_update;
struct tick_sched *tick_get_tick_sched(int cpu)
{
return &per_cpu(tick_cpu_sched, cpu);
}
/*
* Must be called with interrupts disabled !
*/
static void tick_do_update_jiffies64(ktime_t now)
{
unsigned long ticks = 0;
ktime_t delta;
/*
* Do a quick check without holding xtime_lock:
*/
delta = ktime_sub(now, last_jiffies_update);
if (delta.tv64 < tick_period.tv64)
return;
/* Reevalute with xtime_lock held */
write_seqlock(&xtime_lock);
delta = ktime_sub(now, last_jiffies_update);
if (delta.tv64 >= tick_period.tv64) {
delta = ktime_sub(delta, tick_period);
last_jiffies_update = ktime_add(last_jiffies_update,
tick_period);
/* Slow path for long timeouts */
if (unlikely(delta.tv64 >= tick_period.tv64)) {
s64 incr = ktime_to_ns(tick_period);
ticks = ktime_divns(delta, incr);
last_jiffies_update = ktime_add_ns(last_jiffies_update,
incr * ticks);
}
do_timer(++ticks);
/* Keep the tick_next_period variable up to date */
tick_next_period = ktime_add(last_jiffies_update, tick_period);
}
write_sequnlock(&xtime_lock);
}
/*
* Initialize and return retrieve the jiffies update.
*/
static ktime_t tick_init_jiffy_update(void)
{
ktime_t period;
write_seqlock(&xtime_lock);
/* Did we start the jiffies update yet ? */
if (last_jiffies_update.tv64 == 0)
last_jiffies_update = tick_next_period;
period = last_jiffies_update;
write_sequnlock(&xtime_lock);
return period;
}
/*
* NOHZ - aka dynamic tick functionality
*/
#ifdef CONFIG_NO_HZ
/*
* NO HZ enabled ?
*/
int tick_nohz_enabled __read_mostly = 1;
/*
* Enable / Disable tickless mode
*/
static int __init setup_tick_nohz(char *str)
{
if (!strcmp(str, "off"))
tick_nohz_enabled = 0;
else if (!strcmp(str, "on"))
tick_nohz_enabled = 1;
else
return 0;
return 1;
}
__setup("nohz=", setup_tick_nohz);
/**
* 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)
{
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
unsigned long flags;
ts->idle_waketime = now;
local_irq_save(flags);
tick_do_update_jiffies64(now);
local_irq_restore(flags);
touch_softlockup_watchdog();
}
/*
* 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(int cpu, ktime_t now)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
update_ts_time_stats(cpu, ts, now, NULL);
ts->idle_active = 0;
sched_clock_idle_wakeup_event(0);
}
static ktime_t tick_nohz_start_idle(int cpu, struct tick_sched *ts)
{
ktime_t now = ktime_get();
ts->idle_entrytime = now;
ts->idle_active = 1;
sched_clock_idle_sleep_event();
return now;
}
/**
* 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 cummulative 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_enabled)
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 cummulative 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_enabled)
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 ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
ktime_t now, int cpu)
{
unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
ktime_t last_update, expires, ret = { .tv64 = 0 };
unsigned long rcu_delta_jiffies;
struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
u64 time_delta;
/* Read jiffies and the time when jiffies were updated last */
do {
seq = read_seqbegin(&xtime_lock);
last_update = last_jiffies_update;
last_jiffies = jiffies;
time_delta = timekeeping_max_deferment();
} while (read_seqretry(&xtime_lock, seq));
if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || printk_needs_cpu(cpu) ||
arch_needs_cpu(cpu)) {
next_jiffies = last_jiffies + 1;
delta_jiffies = 1;
} else {
/* Get the next timer wheel timer */
next_jiffies = get_next_timer_interrupt(last_jiffies);
delta_jiffies = next_jiffies - last_jiffies;
if (rcu_delta_jiffies < delta_jiffies) {
next_jiffies = last_jiffies + rcu_delta_jiffies;
delta_jiffies = rcu_delta_jiffies;
}
}
/*
* Do not stop the tick, if we are only one off
* or if the cpu is required for rcu
*/
if (!ts->tick_stopped && delta_jiffies == 1)
goto out;
/* Schedule the tick, if we are at least one jiffie off */
if ((long)delta_jiffies >= 1) {
/*
* 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 this cpu is
* the one which had the do_timer() duty last, we
* limit the sleep time to the timekeeping
* max_deferement value which we retrieved
* above. Otherwise we can sleep as long as we want.
*/
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) {
time_delta = KTIME_MAX;
ts->do_timer_last = 0;
} else if (!ts->do_timer_last) {
time_delta = KTIME_MAX;
}
/*
* calculate the expiry time for the next timer wheel
* timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
* that there is no timer pending or at least extremely
* far into the future (12 days for HZ=1000). In this
* case we set the expiry to the end of time.
*/
if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
/*
* Calculate the time delta for the next timer event.
* If the time delta exceeds the maximum time delta
* permitted by the current clocksource then adjust
* the time delta accordingly to ensure the
* clocksource does not wrap.
*/
time_delta = min_t(u64, time_delta,
tick_period.tv64 * delta_jiffies);
}
if (time_delta < KTIME_MAX)
expires = ktime_add_ns(last_update, time_delta);
else
expires.tv64 = KTIME_MAX;
/* Skip reprogram of event if its not changed */
if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
goto out;
ret = expires;
/*
* 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) {
nohz_balance_enter_idle(cpu);
calc_load_enter_idle();
ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
ts->tick_stopped = 1;
}
/*
* If the expiration time == KTIME_MAX, then
* in this case we simply stop the tick timer.
*/
if (unlikely(expires.tv64 == KTIME_MAX)) {
if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
hrtimer_cancel(&ts->sched_timer);
goto out;
}
if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
hrtimer_start(&ts->sched_timer, expires,
HRTIMER_MODE_ABS_PINNED);
/* Check, if the timer was already in the past */
if (hrtimer_active(&ts->sched_timer))
goto out;
} else if (!tick_program_event(expires, 0))
goto out;
/*
* We are past the event already. So we crossed a
* jiffie boundary. Update jiffies and raise the
* softirq.
*/
tick_do_update_jiffies64(ktime_get());
}
raise_softirq_irqoff(TIMER_SOFTIRQ);
out:
ts->next_jiffies = next_jiffies;
ts->last_jiffies = last_jiffies;
ts->sleep_length = ktime_sub(dev->next_event, now);
return ret;
}
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;
}
if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
return false;
if (need_resched())
return false;
if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
static int ratelimit;
if (ratelimit < 10 &&
(local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
(unsigned int) local_softirq_pending());
ratelimit++;
}
return false;
}
return true;
}
static void __tick_nohz_idle_enter(struct tick_sched *ts)
{
ktime_t now, expires;
int cpu = smp_processor_id();
now = tick_nohz_start_idle(cpu, ts);
if (can_stop_idle_tick(cpu, ts)) {
int was_stopped = ts->tick_stopped;
ts->idle_calls++;
expires = tick_nohz_stop_sched_tick(ts, now, cpu);
if (expires.tv64 > 0LL) {
ts->idle_sleeps++;
ts->idle_expires = expires;
}
if (!was_stopped && ts->tick_stopped)
ts->idle_jiffies = ts->last_jiffies;
}
}
/**
* tick_nohz_idle_enter - stop the idle tick from the idle task
*
* When the next event is more than a tick into the future, stop the idle tick
* Called when we start the idle loop.
*
* The arch is responsible of calling:
*
* - rcu_idle_enter() after its last use of RCU before the CPU is put
* to sleep.
* - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
*/
void tick_nohz_idle_enter(void)
{
struct tick_sched *ts;
WARN_ON_ONCE(irqs_disabled());
/*
* Update the idle state in the scheduler domain hierarchy
* when tick_nohz_stop_sched_tick() is called from the idle loop.
* State will be updated to busy during the first busy tick after
* exiting idle.
*/
set_cpu_sd_state_idle();
local_irq_disable();
ts = &__get_cpu_var(tick_cpu_sched);
/*
* set ts->inidle unconditionally. even if the system did not
* switch to nohz mode the cpu frequency governers rely on the
* update of the idle time accounting in tick_nohz_start_idle().
*/
ts->inidle = 1;
__tick_nohz_idle_enter(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 = &__get_cpu_var(tick_cpu_sched);
if (!ts->inidle)
return;
__tick_nohz_idle_enter(ts);
}
/**
* tick_nohz_get_sleep_length - return the length of the current sleep
*
* Called from power state control code with interrupts disabled
*/
ktime_t tick_nohz_get_sleep_length(void)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
return ts->sleep_length;
}
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);
while (1) {
/* Forward the time to expire in the future */
hrtimer_forward(&ts->sched_timer, now, tick_period);
if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
hrtimer_start_expires(&ts->sched_timer,
HRTIMER_MODE_ABS_PINNED);
/* Check, if the timer was already in the past */
if (hrtimer_active(&ts->sched_timer))
break;
} else {
if (!tick_program_event(
hrtimer_get_expires(&ts->sched_timer), 0))
break;
}
/* Reread time and update jiffies */
now = ktime_get();
tick_do_update_jiffies64(now);
}
}
static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
{
/* Update jiffies first */
tick_do_update_jiffies64(now);
update_cpu_load_nohz();
calc_load_exit_idle();
touch_softlockup_watchdog();
/*
* Cancel the scheduled timer and restore the tick
*/
ts->tick_stopped = 0;
ts->idle_exittime = now;
tick_nohz_restart(ts, now);
}
static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
{
#ifndef CONFIG_VIRT_CPU_ACCOUNTING
unsigned long ticks;
/*
* 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);
#endif
}
/**
* 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)
{
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
ktime_t now;
local_irq_disable();
WARN_ON_ONCE(!ts->inidle);
ts->inidle = 0;
if (ts->idle_active || ts->tick_stopped)
now = ktime_get();
if (ts->idle_active)
tick_nohz_stop_idle(cpu, now);
if (ts->tick_stopped) {
tick_nohz_restart_sched_tick(ts, now);
tick_nohz_account_idle_ticks(ts);
}
local_irq_enable();
}
static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
{
hrtimer_forward(&ts->sched_timer, now, tick_period);
return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
}
/*
* The nohz low res interrupt handler
*/
static void tick_nohz_handler(struct clock_event_device *dev)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
struct pt_regs *regs = get_irq_regs();
int cpu = smp_processor_id();
ktime_t now = ktime_get();
dev->next_event.tv64 = KTIME_MAX;
/*
* 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 themself to
* this duty, then the jiffies update is still serialized by
* xtime_lock.
*/
if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
tick_do_timer_cpu = cpu;
/* Check, if the jiffies need an update */
if (tick_do_timer_cpu == cpu)
tick_do_update_jiffies64(now);
/*
* 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();
ts->idle_jiffies++;
}
update_process_times(user_mode(regs));
profile_tick(CPU_PROFILING);
while (tick_nohz_reprogram(ts, now)) {
now = ktime_get();
tick_do_update_jiffies64(now);
}
}
/**
* tick_nohz_switch_to_nohz - switch to nohz mode
*/
static void tick_nohz_switch_to_nohz(void)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
ktime_t next;
if (!tick_nohz_enabled)
return;
local_irq_disable();
if (tick_switch_to_oneshot(tick_nohz_handler)) {
local_irq_enable();
return;
}
ts->nohz_mode = NOHZ_MODE_LOWRES;
/*
* 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);
/* Get the next period */
next = tick_init_jiffy_update();
for (;;) {
hrtimer_set_expires(&ts->sched_timer, next);
if (!tick_program_event(next, 0))
break;
next = ktime_add(next, tick_period);
}
local_irq_enable();
}
/*
* When NOHZ is enabled and the tick is stopped, we need to kick the
* tick timer from irq_enter() so that the jiffies update is kept
* alive during long running softirqs. That's ugly as hell, but
* correctness is key even if we need to fix the offending softirq in
* the first place.
*
* Note, this is different to tick_nohz_restart. We just kick the
* timer and do not touch the other magic bits which need to be done
* when idle is left.
*/
static void tick_nohz_kick_tick(int cpu, ktime_t now)
{
#if 0
/* Switch back to 2.6.27 behaviour */
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
ktime_t delta;
/*
* Do not touch the tick device, when the next expiry is either
* already reached or less/equal than the tick period.
*/
delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
if (delta.tv64 <= tick_period.tv64)
return;
tick_nohz_restart(ts, now);
#endif
}
static inline void tick_check_nohz(int cpu)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
ktime_t now;
if (!ts->idle_active && !ts->tick_stopped)
return;
now = ktime_get();
if (ts->idle_active)
tick_nohz_stop_idle(cpu, now);
if (ts->tick_stopped) {
tick_nohz_update_jiffies(now);
tick_nohz_kick_tick(cpu, now);
}
}
#else
static inline void tick_nohz_switch_to_nohz(void) { }
static inline void tick_check_nohz(int cpu) { }
#endif /* NO_HZ */
/*
* Called from irq_enter to notify about the possible interruption of idle()
*/
void tick_check_idle(int cpu)
{
tick_check_oneshot_broadcast(cpu);
tick_check_nohz(cpu);
}
/*
* 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 and timer->base->cpu_base->lock held.
*/
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();
int cpu = smp_processor_id();
#ifdef CONFIG_NO_HZ
/*
* 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 themself to
* this duty, then the jiffies update is still serialized by
* xtime_lock.
*/
if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
tick_do_timer_cpu = cpu;
#endif
/* Check, if the jiffies need an update */
if (tick_do_timer_cpu == cpu)
tick_do_update_jiffies64(now);
/*
* Do not call, when we are not in irq context and have
* no valid regs pointer
*/
if (regs) {
/*
* 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();
if (is_idle_task(current))
ts->idle_jiffies++;
}
update_process_times(user_mode(regs));
profile_tick(CPU_PROFILING);
}
hrtimer_forward(timer, now, tick_period);
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 = &__get_cpu_var(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);
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 xtime_lock contention. */
if (sched_skew_tick) {
u64 offset = ktime_to_ns(tick_period) >> 1;
do_div(offset, num_possible_cpus());
offset *= smp_processor_id();
hrtimer_add_expires_ns(&ts->sched_timer, offset);
}
for (;;) {
hrtimer_forward(&ts->sched_timer, now, tick_period);
hrtimer_start_expires(&ts->sched_timer,
HRTIMER_MODE_ABS_PINNED);
/* Check, if the timer was already in the past */
if (hrtimer_active(&ts->sched_timer))
break;
now = ktime_get();
}
#ifdef CONFIG_NO_HZ
if (tick_nohz_enabled)
ts->nohz_mode = NOHZ_MODE_HIGHRES;
#endif
}
#endif /* HIGH_RES_TIMERS */
#if defined CONFIG_NO_HZ || 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
ts->nohz_mode = NOHZ_MODE_INACTIVE;
}
#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 = &__get_cpu_var(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).
*/
int tick_check_oneshot_change(int allow_nohz)
{
struct tick_sched *ts = &__get_cpu_var(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;
}