![Thomas Gleixner](/assets/img/avatar_default.png)
If nohz is disabled on the kernel command line the [hr]timer code still calls wake_up_nohz_cpu() and tick_nohz_full_cpu(), a pretty pointless exercise. Cache nohz_active in [hr]timer per cpu bases and avoid the overhead. Before: 48.10% hog [.] main 15.25% [kernel] [k] _raw_spin_lock_irqsave 9.76% [kernel] [k] _raw_spin_unlock_irqrestore 6.50% [kernel] [k] mod_timer 6.44% [kernel] [k] lock_timer_base.isra.38 3.87% [kernel] [k] detach_if_pending 3.80% [kernel] [k] del_timer 2.67% [kernel] [k] internal_add_timer 1.33% [kernel] [k] __internal_add_timer 0.73% [kernel] [k] timerfn 0.54% [kernel] [k] wake_up_nohz_cpu After: 48.73% hog [.] main 15.36% [kernel] [k] _raw_spin_lock_irqsave 9.77% [kernel] [k] _raw_spin_unlock_irqrestore 6.61% [kernel] [k] lock_timer_base.isra.38 6.42% [kernel] [k] mod_timer 3.90% [kernel] [k] detach_if_pending 3.76% [kernel] [k] del_timer 2.41% [kernel] [k] internal_add_timer 1.39% [kernel] [k] __internal_add_timer 0.76% [kernel] [k] timerfn We probably should have a cached value for nohz full in the per cpu bases as well to avoid the cpumask check. The base cache line is hot already, the cpumask not necessarily. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: John Stultz <john.stultz@linaro.org> Cc: Joonwoo Park <joonwoop@codeaurora.org> Cc: Wenbo Wang <wenbo.wang@memblaze.com> Link: http://lkml.kernel.org/r/20150526224512.207378134@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
1195 lines
29 KiB
C
1195 lines
29 KiB
C
/*
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* linux/kernel/time/tick-sched.c
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*
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* Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
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* Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
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* Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner
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*
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* No idle tick implementation for low and high resolution timers
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*
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* Started by: Thomas Gleixner and Ingo Molnar
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*
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* Distribute under GPLv2.
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*/
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#include <linux/cpu.h>
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#include <linux/err.h>
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#include <linux/hrtimer.h>
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#include <linux/interrupt.h>
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#include <linux/kernel_stat.h>
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#include <linux/percpu.h>
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#include <linux/profile.h>
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#include <linux/sched.h>
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#include <linux/module.h>
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#include <linux/irq_work.h>
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#include <linux/posix-timers.h>
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#include <linux/perf_event.h>
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#include <linux/context_tracking.h>
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#include <asm/irq_regs.h>
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#include "tick-internal.h"
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#include <trace/events/timer.h>
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/*
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* Per cpu nohz control structure
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*/
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static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
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/*
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* The time, when the last jiffy update happened. Protected by jiffies_lock.
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*/
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static ktime_t last_jiffies_update;
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struct tick_sched *tick_get_tick_sched(int cpu)
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{
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return &per_cpu(tick_cpu_sched, cpu);
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}
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/*
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* Must be called with interrupts disabled !
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*/
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static void tick_do_update_jiffies64(ktime_t now)
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{
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unsigned long ticks = 0;
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ktime_t delta;
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/*
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* Do a quick check without holding jiffies_lock:
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*/
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delta = ktime_sub(now, last_jiffies_update);
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if (delta.tv64 < tick_period.tv64)
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return;
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/* Reevalute with jiffies_lock held */
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write_seqlock(&jiffies_lock);
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delta = ktime_sub(now, last_jiffies_update);
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if (delta.tv64 >= tick_period.tv64) {
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delta = ktime_sub(delta, tick_period);
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last_jiffies_update = ktime_add(last_jiffies_update,
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tick_period);
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/* Slow path for long timeouts */
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if (unlikely(delta.tv64 >= tick_period.tv64)) {
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s64 incr = ktime_to_ns(tick_period);
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ticks = ktime_divns(delta, incr);
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last_jiffies_update = ktime_add_ns(last_jiffies_update,
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incr * ticks);
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}
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do_timer(++ticks);
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/* Keep the tick_next_period variable up to date */
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tick_next_period = ktime_add(last_jiffies_update, tick_period);
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} else {
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write_sequnlock(&jiffies_lock);
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return;
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}
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write_sequnlock(&jiffies_lock);
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update_wall_time();
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}
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/*
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* Initialize and return retrieve the jiffies update.
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*/
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static ktime_t tick_init_jiffy_update(void)
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{
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ktime_t period;
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write_seqlock(&jiffies_lock);
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/* Did we start the jiffies update yet ? */
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if (last_jiffies_update.tv64 == 0)
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last_jiffies_update = tick_next_period;
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period = last_jiffies_update;
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write_sequnlock(&jiffies_lock);
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return period;
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}
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static void tick_sched_do_timer(ktime_t now)
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{
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int cpu = smp_processor_id();
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#ifdef CONFIG_NO_HZ_COMMON
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/*
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* Check if the do_timer duty was dropped. We don't care about
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* concurrency: This happens only when the cpu in charge went
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* into a long sleep. If two cpus happen to assign themself to
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* this duty, then the jiffies update is still serialized by
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* jiffies_lock.
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*/
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if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
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&& !tick_nohz_full_cpu(cpu))
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tick_do_timer_cpu = cpu;
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#endif
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/* Check, if the jiffies need an update */
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if (tick_do_timer_cpu == cpu)
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tick_do_update_jiffies64(now);
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}
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static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
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{
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#ifdef CONFIG_NO_HZ_COMMON
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/*
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* When we are idle and the tick is stopped, we have to touch
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* the watchdog as we might not schedule for a really long
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* time. This happens on complete idle SMP systems while
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* waiting on the login prompt. We also increment the "start of
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* idle" jiffy stamp so the idle accounting adjustment we do
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* when we go busy again does not account too much ticks.
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*/
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if (ts->tick_stopped) {
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touch_softlockup_watchdog();
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if (is_idle_task(current))
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ts->idle_jiffies++;
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}
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#endif
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update_process_times(user_mode(regs));
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profile_tick(CPU_PROFILING);
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}
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#ifdef CONFIG_NO_HZ_FULL
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cpumask_var_t tick_nohz_full_mask;
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cpumask_var_t housekeeping_mask;
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bool tick_nohz_full_running;
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static bool can_stop_full_tick(void)
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{
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WARN_ON_ONCE(!irqs_disabled());
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if (!sched_can_stop_tick()) {
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trace_tick_stop(0, "more than 1 task in runqueue\n");
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return false;
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}
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if (!posix_cpu_timers_can_stop_tick(current)) {
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trace_tick_stop(0, "posix timers running\n");
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return false;
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}
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if (!perf_event_can_stop_tick()) {
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trace_tick_stop(0, "perf events running\n");
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return false;
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}
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/* sched_clock_tick() needs us? */
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#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
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/*
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* TODO: kick full dynticks CPUs when
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* sched_clock_stable is set.
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*/
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if (!sched_clock_stable()) {
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trace_tick_stop(0, "unstable sched clock\n");
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/*
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* Don't allow the user to think they can get
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* full NO_HZ with this machine.
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*/
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WARN_ONCE(tick_nohz_full_running,
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"NO_HZ FULL will not work with unstable sched clock");
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return false;
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}
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#endif
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return true;
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}
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static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
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/*
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* Re-evaluate the need for the tick on the current CPU
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* and restart it if necessary.
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*/
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void __tick_nohz_full_check(void)
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{
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struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
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if (tick_nohz_full_cpu(smp_processor_id())) {
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if (ts->tick_stopped && !is_idle_task(current)) {
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if (!can_stop_full_tick())
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tick_nohz_restart_sched_tick(ts, ktime_get());
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}
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}
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}
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static void nohz_full_kick_work_func(struct irq_work *work)
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{
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__tick_nohz_full_check();
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}
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static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
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.func = nohz_full_kick_work_func,
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};
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/*
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* Kick this CPU if it's full dynticks in order to force it to
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* re-evaluate its dependency on the tick and restart it if necessary.
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* This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
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* is NMI safe.
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*/
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void tick_nohz_full_kick(void)
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{
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if (!tick_nohz_full_cpu(smp_processor_id()))
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return;
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irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
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}
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/*
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* Kick the CPU if it's full dynticks in order to force it to
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* re-evaluate its dependency on the tick and restart it if necessary.
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*/
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void tick_nohz_full_kick_cpu(int cpu)
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{
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if (!tick_nohz_full_cpu(cpu))
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return;
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irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
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}
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static void nohz_full_kick_ipi(void *info)
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{
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__tick_nohz_full_check();
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}
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/*
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* Kick all full dynticks CPUs in order to force these to re-evaluate
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* their dependency on the tick and restart it if necessary.
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*/
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void tick_nohz_full_kick_all(void)
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{
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if (!tick_nohz_full_running)
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return;
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preempt_disable();
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smp_call_function_many(tick_nohz_full_mask,
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nohz_full_kick_ipi, NULL, false);
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tick_nohz_full_kick();
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preempt_enable();
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}
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/*
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* Re-evaluate the need for the tick as we switch the current task.
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* It might need the tick due to per task/process properties:
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* perf events, posix cpu timers, ...
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*/
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void __tick_nohz_task_switch(struct task_struct *tsk)
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{
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unsigned long flags;
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local_irq_save(flags);
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if (!tick_nohz_full_cpu(smp_processor_id()))
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goto out;
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if (tick_nohz_tick_stopped() && !can_stop_full_tick())
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tick_nohz_full_kick();
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out:
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local_irq_restore(flags);
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}
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/* Parse the boot-time nohz CPU list from the kernel parameters. */
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static int __init tick_nohz_full_setup(char *str)
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{
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alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
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if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
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pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
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free_bootmem_cpumask_var(tick_nohz_full_mask);
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return 1;
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}
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tick_nohz_full_running = true;
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return 1;
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}
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__setup("nohz_full=", tick_nohz_full_setup);
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static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
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unsigned long action,
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void *hcpu)
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{
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unsigned int cpu = (unsigned long)hcpu;
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switch (action & ~CPU_TASKS_FROZEN) {
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case CPU_DOWN_PREPARE:
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/*
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* If we handle the timekeeping duty for full dynticks CPUs,
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* we can't safely shutdown that CPU.
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*/
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if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
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return NOTIFY_BAD;
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break;
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}
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return NOTIFY_OK;
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}
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static int tick_nohz_init_all(void)
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{
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int err = -1;
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#ifdef CONFIG_NO_HZ_FULL_ALL
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if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
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WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
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return err;
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}
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err = 0;
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cpumask_setall(tick_nohz_full_mask);
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tick_nohz_full_running = true;
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#endif
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return err;
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}
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void __init tick_nohz_init(void)
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{
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int cpu;
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if (!tick_nohz_full_running) {
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if (tick_nohz_init_all() < 0)
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return;
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}
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if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
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WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
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cpumask_clear(tick_nohz_full_mask);
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tick_nohz_full_running = false;
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return;
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}
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/*
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* Full dynticks uses irq work to drive the tick rescheduling on safe
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* locking contexts. But then we need irq work to raise its own
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* interrupts to avoid circular dependency on the tick
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*/
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if (!arch_irq_work_has_interrupt()) {
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pr_warning("NO_HZ: Can't run full dynticks because arch doesn't "
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"support irq work self-IPIs\n");
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cpumask_clear(tick_nohz_full_mask);
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cpumask_copy(housekeeping_mask, cpu_possible_mask);
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tick_nohz_full_running = false;
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return;
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}
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cpu = smp_processor_id();
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if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
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pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
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cpumask_clear_cpu(cpu, tick_nohz_full_mask);
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}
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cpumask_andnot(housekeeping_mask,
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cpu_possible_mask, tick_nohz_full_mask);
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for_each_cpu(cpu, tick_nohz_full_mask)
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context_tracking_cpu_set(cpu);
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cpu_notifier(tick_nohz_cpu_down_callback, 0);
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pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
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cpumask_pr_args(tick_nohz_full_mask));
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}
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#endif
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/*
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* NOHZ - aka dynamic tick functionality
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*/
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#ifdef CONFIG_NO_HZ_COMMON
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/*
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* NO HZ enabled ?
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*/
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static int tick_nohz_enabled __read_mostly = 1;
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unsigned long tick_nohz_active __read_mostly;
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/*
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* Enable / Disable tickless mode
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*/
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static int __init setup_tick_nohz(char *str)
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{
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if (!strcmp(str, "off"))
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tick_nohz_enabled = 0;
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else if (!strcmp(str, "on"))
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tick_nohz_enabled = 1;
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else
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return 0;
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return 1;
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}
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__setup("nohz=", setup_tick_nohz);
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int tick_nohz_tick_stopped(void)
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{
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return __this_cpu_read(tick_cpu_sched.tick_stopped);
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}
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/**
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* tick_nohz_update_jiffies - update jiffies when idle was interrupted
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*
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* Called from interrupt entry when the CPU was idle
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*
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* In case the sched_tick was stopped on this CPU, we have to check if jiffies
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* must be updated. Otherwise an interrupt handler could use a stale jiffy
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* value. We do this unconditionally on any cpu, as we don't know whether the
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* cpu, which has the update task assigned is in a long sleep.
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*/
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static void tick_nohz_update_jiffies(ktime_t now)
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{
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unsigned long flags;
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__this_cpu_write(tick_cpu_sched.idle_waketime, now);
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local_irq_save(flags);
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tick_do_update_jiffies64(now);
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local_irq_restore(flags);
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touch_softlockup_watchdog();
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}
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/*
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* Updates the per cpu time idle statistics counters
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*/
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static void
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update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
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{
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ktime_t delta;
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if (ts->idle_active) {
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delta = ktime_sub(now, ts->idle_entrytime);
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if (nr_iowait_cpu(cpu) > 0)
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ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
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else
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ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
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ts->idle_entrytime = now;
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}
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if (last_update_time)
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*last_update_time = ktime_to_us(now);
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}
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static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
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{
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update_ts_time_stats(smp_processor_id(), ts, now, NULL);
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ts->idle_active = 0;
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sched_clock_idle_wakeup_event(0);
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}
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|
static ktime_t tick_nohz_start_idle(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_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 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_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_period);
|
|
|
|
if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
|
|
hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
|
|
else
|
|
tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
|
|
}
|
|
|
|
static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
|
|
ktime_t now, int cpu)
|
|
{
|
|
struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
|
|
u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
|
|
unsigned long seq, basejiff;
|
|
ktime_t tick;
|
|
|
|
/* Read jiffies and the time when jiffies were updated last */
|
|
do {
|
|
seq = read_seqbegin(&jiffies_lock);
|
|
basemono = last_jiffies_update.tv64;
|
|
basejiff = jiffies;
|
|
} while (read_seqretry(&jiffies_lock, seq));
|
|
ts->last_jiffies = basejiff;
|
|
|
|
if (rcu_needs_cpu(basemono, &next_rcu) ||
|
|
arch_needs_cpu() || irq_work_needs_cpu()) {
|
|
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
|
|
* restart it proper.
|
|
*/
|
|
delta = next_tick - basemono;
|
|
if (delta <= (u64)TICK_NSEC) {
|
|
tick.tv64 = 0;
|
|
if (!ts->tick_stopped)
|
|
goto out;
|
|
if (delta == 0) {
|
|
/* Tick is stopped, but required now. Enforce it */
|
|
tick_nohz_restart(ts, now);
|
|
goto out;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
* 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 = 1;
|
|
} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
|
|
delta = KTIME_MAX;
|
|
ts->do_timer_last = 0;
|
|
} else if (!ts->do_timer_last) {
|
|
delta = KTIME_MAX;
|
|
}
|
|
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
/* Limit the tick delta to the maximum scheduler deferment */
|
|
if (!ts->inidle)
|
|
delta = min(delta, scheduler_tick_max_deferment());
|
|
#endif
|
|
|
|
/* Calculate the next expiry time */
|
|
if (delta < (KTIME_MAX - basemono))
|
|
expires = basemono + delta;
|
|
else
|
|
expires = KTIME_MAX;
|
|
|
|
expires = min_t(u64, expires, next_tick);
|
|
tick.tv64 = expires;
|
|
|
|
/* Skip reprogram of event if its not changed */
|
|
if (ts->tick_stopped && (expires == dev->next_event.tv64))
|
|
goto out;
|
|
|
|
/*
|
|
* 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;
|
|
trace_tick_stop(1, " ");
|
|
}
|
|
|
|
/*
|
|
* 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);
|
|
goto out;
|
|
}
|
|
|
|
if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
|
|
hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
|
|
else
|
|
tick_program_event(tick, 1);
|
|
out:
|
|
/* Update the estimated sleep length */
|
|
ts->sleep_length = ktime_sub(dev->next_event, now);
|
|
return tick;
|
|
}
|
|
|
|
static void tick_nohz_full_stop_tick(struct tick_sched *ts)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
int cpu = smp_processor_id();
|
|
|
|
if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
|
|
return;
|
|
|
|
if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
|
|
return;
|
|
|
|
if (!can_stop_full_tick())
|
|
return;
|
|
|
|
tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
|
|
#endif
|
|
}
|
|
|
|
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;
|
|
return false;
|
|
}
|
|
|
|
if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
|
|
ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
|
|
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)) {
|
|
pr_warn("NOHZ: local_softirq_pending %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;
|
|
/*
|
|
* Boot safety: make sure the timekeeping duty has been
|
|
* assigned before entering dyntick-idle mode,
|
|
*/
|
|
if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
|
|
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(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 = this_cpu_ptr(&tick_cpu_sched);
|
|
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 = this_cpu_ptr(&tick_cpu_sched);
|
|
|
|
if (ts->inidle)
|
|
__tick_nohz_idle_enter(ts);
|
|
else
|
|
tick_nohz_full_stop_tick(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 = this_cpu_ptr(&tick_cpu_sched);
|
|
|
|
return ts->sleep_length;
|
|
}
|
|
|
|
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_NATIVE
|
|
unsigned long ticks;
|
|
|
|
if (vtime_accounting_enabled())
|
|
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);
|
|
#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)
|
|
{
|
|
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
|
|
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(ts, now);
|
|
|
|
if (ts->tick_stopped) {
|
|
tick_nohz_restart_sched_tick(ts, now);
|
|
tick_nohz_account_idle_ticks(ts);
|
|
}
|
|
|
|
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.tv64 = KTIME_MAX;
|
|
|
|
tick_sched_do_timer(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_period);
|
|
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_migration(true);
|
|
}
|
|
|
|
/**
|
|
* 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);
|
|
/* Get the next period */
|
|
next = tick_init_jiffy_update();
|
|
|
|
hrtimer_forward_now(&ts->sched_timer, tick_period);
|
|
hrtimer_set_expires(&ts->sched_timer, next);
|
|
tick_program_event(next, 1);
|
|
tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
|
|
}
|
|
|
|
/*
|
|
* 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(struct tick_sched *ts, ktime_t now)
|
|
{
|
|
#if 0
|
|
/* Switch back to 2.6.27 behaviour */
|
|
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_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);
|
|
tick_nohz_kick_tick(ts, 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(now);
|
|
|
|
/*
|
|
* Do not call, when we are not in irq context and have
|
|
* no valid regs pointer
|
|
*/
|
|
if (regs)
|
|
tick_sched_handle(ts, regs);
|
|
|
|
/* 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_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 = 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);
|
|
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 = ktime_to_ns(tick_period) >> 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_period);
|
|
hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
|
|
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;
|
|
}
|