kernel-ark/kernel/time/tick-sched.c
Thomas Gleixner 5e41d0d60a clockevents: prevent stale tick update on offline cpu
Taking a cpu offline removes the cpu from the online mask before the
CPU_DEAD notification is done. The clock events layer does the cleanup
of the dead CPU from the CPU_DEAD notifier chain. tick_do_timer_cpu is
used to avoid xtime lock contention by assigning the task of jiffies
xtime updates to one CPU. If a CPU is taken offline, then this
assignment becomes stale. This went unnoticed because most of the time
the offline CPU went dead before the online CPU reached __cpu_die(),
where the CPU_DEAD state is checked. In the case that the offline CPU did
not reach the DEAD state before we reach __cpu_die(), the code in there
goes to sleep for 100ms. Due to the stale time update assignment, the
system is stuck forever.

Take the assignment away when a cpu is not longer in the cpu_online_mask.
We do this in the last call to tick_nohz_stop_sched_tick() when the offline
CPU is on the way to the final play_dead() idle entry.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2007-09-16 15:36:43 +02:00

652 lines
16 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
*
* For licencing details see kernel-base/COPYING
*/
#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/tick.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;
/* 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);
}
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 ?
*/
static 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.
*/
void tick_nohz_update_jiffies(void)
{
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
unsigned long flags;
ktime_t now;
if (!ts->tick_stopped)
return;
cpu_clear(cpu, nohz_cpu_mask);
now = ktime_get();
local_irq_save(flags);
tick_do_update_jiffies64(now);
local_irq_restore(flags);
}
/**
* tick_nohz_stop_sched_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
* Called either from the idle loop or from irq_exit() when an idle period was
* just interrupted by an interrupt which did not cause a reschedule.
*/
void tick_nohz_stop_sched_tick(void)
{
unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
struct tick_sched *ts;
ktime_t last_update, expires, now, delta;
int cpu;
local_irq_save(flags);
cpu = smp_processor_id();
ts = &per_cpu(tick_cpu_sched, cpu);
/*
* 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 = -1;
}
if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
goto end;
if (need_resched())
goto end;
cpu = smp_processor_id();
if (unlikely(local_softirq_pending())) {
static int ratelimit;
if (ratelimit < 10) {
printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
local_softirq_pending());
ratelimit++;
}
}
now = ktime_get();
/*
* When called from irq_exit we need to account the idle sleep time
* correctly.
*/
if (ts->tick_stopped) {
delta = ktime_sub(now, ts->idle_entrytime);
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
}
ts->idle_entrytime = now;
ts->idle_calls++;
/* Read jiffies and the time when jiffies were updated last */
do {
seq = read_seqbegin(&xtime_lock);
last_update = last_jiffies_update;
last_jiffies = jiffies;
} while (read_seqretry(&xtime_lock, seq));
/* Get the next timer wheel timer */
next_jiffies = get_next_timer_interrupt(last_jiffies);
delta_jiffies = next_jiffies - last_jiffies;
if (rcu_needs_cpu(cpu))
delta_jiffies = 1;
/*
* 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 (delta_jiffies > 1)
cpu_set(cpu, nohz_cpu_mask);
/*
* 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) {
if (select_nohz_load_balancer(1)) {
/*
* sched tick not stopped!
*/
cpu_clear(cpu, nohz_cpu_mask);
goto out;
}
ts->idle_tick = ts->sched_timer.expires;
ts->tick_stopped = 1;
ts->idle_jiffies = last_jiffies;
}
/*
* 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.
*/
if (cpu == tick_do_timer_cpu)
tick_do_timer_cpu = -1;
ts->idle_sleeps++;
/*
* delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that
* there is no timer pending or at least extremly far
* into the future (12 days for HZ=1000). In this case
* we simply stop the tick timer:
*/
if (unlikely(delta_jiffies >= NEXT_TIMER_MAX_DELTA)) {
ts->idle_expires.tv64 = KTIME_MAX;
if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
hrtimer_cancel(&ts->sched_timer);
goto out;
}
/*
* calculate the expiry time for the next timer wheel
* timer
*/
expires = ktime_add_ns(last_update, tick_period.tv64 *
delta_jiffies);
ts->idle_expires = expires;
if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
hrtimer_start(&ts->sched_timer, expires,
HRTIMER_MODE_ABS);
/* 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());
cpu_clear(cpu, nohz_cpu_mask);
}
raise_softirq_irqoff(TIMER_SOFTIRQ);
out:
ts->next_jiffies = next_jiffies;
ts->last_jiffies = last_jiffies;
end:
local_irq_restore(flags);
}
/**
* nohz_restart_sched_tick - restart the idle tick from the idle task
*
* Restart the idle tick when the CPU is woken up from idle
*/
void tick_nohz_restart_sched_tick(void)
{
int cpu = smp_processor_id();
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
unsigned long ticks;
ktime_t now, delta;
if (!ts->tick_stopped)
return;
/* Update jiffies first */
now = ktime_get();
local_irq_disable();
select_nohz_load_balancer(0);
tick_do_update_jiffies64(now);
cpu_clear(cpu, nohz_cpu_mask);
/* Account the idle time */
delta = ktime_sub(now, ts->idle_entrytime);
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
/*
* 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) {
add_preempt_count(HARDIRQ_OFFSET);
account_system_time(current, HARDIRQ_OFFSET,
jiffies_to_cputime(ticks));
sub_preempt_count(HARDIRQ_OFFSET);
}
/*
* Cancel the scheduled timer and restore the tick
*/
ts->tick_stopped = 0;
hrtimer_cancel(&ts->sched_timer);
ts->sched_timer.expires = ts->idle_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(&ts->sched_timer,
ts->sched_timer.expires,
HRTIMER_MODE_ABS);
/* Check, if the timer was already in the past */
if (hrtimer_active(&ts->sched_timer))
break;
} else {
if (!tick_program_event(ts->sched_timer.expires, 0))
break;
}
/* Update jiffies and reread time */
tick_do_update_jiffies64(now);
now = ktime_get();
}
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(ts->sched_timer.expires, 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 == -1))
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);
/* Do not restart, when we are in the idle loop */
if (ts->tick_stopped)
return;
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 (;;) {
ts->sched_timer.expires = next;
if (!tick_program_event(next, 0))
break;
next = ktime_add(next, tick_period);
}
local_irq_enable();
printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
smp_processor_id());
}
#else
static inline void tick_nohz_switch_to_nohz(void) { }
#endif /* NO_HZ */
/*
* 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 hrtimer_cpu_base *base = timer->base->cpu_base;
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 == -1))
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();
ts->idle_jiffies++;
}
/*
* update_process_times() might take tasklist_lock, hence
* drop the base lock. sched-tick hrtimers are per-CPU and
* never accessible by userspace APIs, so this is safe to do.
*/
spin_unlock(&base->lock);
update_process_times(user_mode(regs));
profile_tick(CPU_PROFILING);
spin_lock(&base->lock);
}
/* Do not restart, when we are in the idle loop */
if (ts->tick_stopped)
return HRTIMER_NORESTART;
hrtimer_forward(timer, now, tick_period);
return HRTIMER_RESTART;
}
/**
* 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();
u64 offset;
/*
* Emulate tick processing via per-CPU hrtimers:
*/
hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
ts->sched_timer.function = tick_sched_timer;
ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
/* Get the next period (per cpu) */
ts->sched_timer.expires = tick_init_jiffy_update();
offset = ktime_to_ns(tick_period) >> 1;
do_div(offset, NR_CPUS);
offset *= smp_processor_id();
ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);
for (;;) {
hrtimer_forward(&ts->sched_timer, now, tick_period);
hrtimer_start(&ts->sched_timer, ts->sched_timer.expires,
HRTIMER_MODE_ABS);
/* 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
}
void tick_cancel_sched_timer(int cpu)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
if (ts->sched_timer.base)
hrtimer_cancel(&ts->sched_timer);
ts->tick_stopped = 0;
ts->nohz_mode = NOHZ_MODE_INACTIVE;
}
#endif /* HIGH_RES_TIMERS */
/**
* 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_is_continuous() || !tick_is_oneshot_available())
return 0;
if (!allow_nohz)
return 1;
tick_nohz_switch_to_nohz();
return 0;
}