![Rafael J. Wysocki](/assets/img/avatar_default.png)
The way the schedutil governor uses the PELT metric causes it to underestimate the CPU utilization in some cases. That can be easily demonstrated by running kernel compilation on a Sandy Bridge Intel processor, running turbostat in parallel with it and looking at the values written to the MSR_IA32_PERF_CTL register. Namely, the expected result would be that when all CPUs were 100% busy, all of them would be requested to run in the maximum P-state, but observation shows that this clearly isn't the case. The CPUs run in the maximum P-state for a while and then are requested to run slower and go back to the maximum P-state after a while again. That causes the actual frequency of the processor to visibly oscillate below the sustainable maximum in a jittery fashion which clearly is not desirable. That has been attributed to CPU utilization metric updates on task migration that cause the total utilization value for the CPU to be reduced by the utilization of the migrated task. If that happens, the schedutil governor may see a CPU utilization reduction and will attempt to reduce the CPU frequency accordingly right away. That may be premature, though, for example if the system is generally busy and there are other runnable tasks waiting to be run on that CPU already. This is unlikely to be an issue on systems where cpufreq policies are shared between multiple CPUs, because in those cases the policy utilization is computed as the maximum of the CPU utilization values over the whole policy and if that turns out to be low, reducing the frequency for the policy most likely is a good idea anyway. On systems with one CPU per policy, however, it may affect performance adversely and even lead to increased energy consumption in some cases. On those systems it may be addressed by taking another utilization metric into consideration, like whether or not the CPU whose frequency is about to be reduced has been idle recently, because if that's not the case, the CPU is likely to be busy in the near future and its frequency should not be reduced. To that end, use the counter of idle calls in the timekeeping code. Namely, make the schedutil governor look at that counter for the current CPU every time before its frequency is about to be reduced. If the counter has not changed since the previous iteration of the governor computations for that CPU, the CPU has been busy for all that time and its frequency should not be decreased, so if the new frequency would be lower than the one set previously, the governor will skip the frequency update. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Joel Fernandes <joelaf@google.com>
1288 lines
31 KiB
C
1288 lines
31 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/nmi.h>
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#include <linux/profile.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/clock.h>
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#include <linux/sched/stat.h>
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#include <linux/sched/nohz.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/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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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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#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
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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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/*
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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 < tick_period)
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return;
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/* Reevaluate 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 >= tick_period) {
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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 >= tick_period)) {
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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 == 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 themselves 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_sched();
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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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#endif
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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 atomic_t tick_dep_mask;
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static bool check_tick_dependency(atomic_t *dep)
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{
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int val = atomic_read(dep);
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if (val & TICK_DEP_MASK_POSIX_TIMER) {
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trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
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return true;
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}
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if (val & TICK_DEP_MASK_PERF_EVENTS) {
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trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
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return true;
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}
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if (val & TICK_DEP_MASK_SCHED) {
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trace_tick_stop(0, TICK_DEP_MASK_SCHED);
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return true;
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}
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if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
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trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
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return true;
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}
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return false;
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}
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static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
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{
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WARN_ON_ONCE(!irqs_disabled());
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if (unlikely(!cpu_online(cpu)))
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return false;
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if (check_tick_dependency(&tick_dep_mask))
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return false;
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if (check_tick_dependency(&ts->tick_dep_mask))
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return false;
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if (check_tick_dependency(¤t->tick_dep_mask))
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return false;
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if (check_tick_dependency(¤t->signal->tick_dep_mask))
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return false;
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return true;
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}
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static void nohz_full_kick_func(struct irq_work *work)
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{
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/* Empty, the tick restart happens on tick_nohz_irq_exit() */
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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_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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static 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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/*
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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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static void tick_nohz_full_kick_all(void)
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{
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int cpu;
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if (!tick_nohz_full_running)
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return;
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preempt_disable();
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for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
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tick_nohz_full_kick_cpu(cpu);
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preempt_enable();
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}
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static void tick_nohz_dep_set_all(atomic_t *dep,
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enum tick_dep_bits bit)
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{
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int prev;
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prev = atomic_fetch_or(BIT(bit), dep);
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if (!prev)
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tick_nohz_full_kick_all();
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}
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/*
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* Set a global tick dependency. Used by perf events that rely on freq and
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* by unstable clock.
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*/
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void tick_nohz_dep_set(enum tick_dep_bits bit)
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{
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tick_nohz_dep_set_all(&tick_dep_mask, bit);
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}
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void tick_nohz_dep_clear(enum tick_dep_bits bit)
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{
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atomic_andnot(BIT(bit), &tick_dep_mask);
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}
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/*
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* Set per-CPU tick dependency. Used by scheduler and perf events in order to
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* manage events throttling.
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*/
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void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
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{
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int prev;
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struct tick_sched *ts;
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ts = per_cpu_ptr(&tick_cpu_sched, cpu);
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prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
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if (!prev) {
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preempt_disable();
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/* Perf needs local kick that is NMI safe */
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if (cpu == smp_processor_id()) {
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tick_nohz_full_kick();
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} else {
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/* Remote irq work not NMI-safe */
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if (!WARN_ON_ONCE(in_nmi()))
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tick_nohz_full_kick_cpu(cpu);
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}
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preempt_enable();
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}
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}
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void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
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{
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struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
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atomic_andnot(BIT(bit), &ts->tick_dep_mask);
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}
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/*
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* Set a per-task tick dependency. Posix CPU timers need this in order to elapse
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* per task timers.
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*/
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void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
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{
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/*
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* We could optimize this with just kicking the target running the task
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* if that noise matters for nohz full users.
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*/
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tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
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}
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void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
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{
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atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
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}
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/*
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* Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
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* per process timers.
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*/
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void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
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{
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tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
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}
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void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
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{
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atomic_andnot(BIT(bit), &sig->tick_dep_mask);
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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(void)
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{
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unsigned long flags;
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struct tick_sched *ts;
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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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ts = this_cpu_ptr(&tick_cpu_sched);
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if (ts->tick_stopped) {
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if (atomic_read(¤t->tick_dep_mask) ||
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atomic_read(¤t->signal->tick_dep_mask))
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tick_nohz_full_kick();
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}
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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_warn("NO_HZ: 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(unsigned int cpu)
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{
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/*
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* The boot CPU handles housekeeping duty (unbound timers,
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* workqueues, timekeeping, ...) on behalf of full dynticks
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* CPUs. It must remain online when nohz full is enabled.
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*/
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if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
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return -EBUSY;
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return 0;
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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, ret;
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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_warn("NO_HZ: Can't run full dynticks because arch doesn't 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_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
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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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ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
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"kernel/nohz:predown", NULL,
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tick_nohz_cpu_down);
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WARN_ON(ret < 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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* We need at least one CPU to handle housekeeping work such
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* as timekeeping, unbound timers, workqueues, ...
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*/
|
|
WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* NOHZ - aka dynamic tick functionality
|
|
*/
|
|
#ifdef CONFIG_NO_HZ_COMMON
|
|
/*
|
|
* NO HZ enabled ?
|
|
*/
|
|
bool tick_nohz_enabled __read_mostly = true;
|
|
unsigned long tick_nohz_active __read_mostly;
|
|
/*
|
|
* Enable / Disable tickless mode
|
|
*/
|
|
static int __init setup_tick_nohz(char *str)
|
|
{
|
|
return (kstrtobool(str, &tick_nohz_enabled) == 0);
|
|
}
|
|
|
|
__setup("nohz=", setup_tick_nohz);
|
|
|
|
int tick_nohz_tick_stopped(void)
|
|
{
|
|
return __this_cpu_read(tick_cpu_sched.tick_stopped);
|
|
}
|
|
|
|
/**
|
|
* tick_nohz_update_jiffies - update jiffies when idle was interrupted
|
|
*
|
|
* Called from interrupt entry when the CPU was idle
|
|
*
|
|
* In case the sched_tick was stopped on this CPU, we have to check if jiffies
|
|
* must be updated. Otherwise an interrupt handler could use a stale jiffy
|
|
* value. We do this unconditionally on any CPU, as we don't know whether the
|
|
* CPU, which has the update task assigned is in a long sleep.
|
|
*/
|
|
static void tick_nohz_update_jiffies(ktime_t now)
|
|
{
|
|
unsigned long flags;
|
|
|
|
__this_cpu_write(tick_cpu_sched.idle_waketime, now);
|
|
|
|
local_irq_save(flags);
|
|
tick_do_update_jiffies64(now);
|
|
local_irq_restore(flags);
|
|
|
|
touch_softlockup_watchdog_sched();
|
|
}
|
|
|
|
/*
|
|
* Updates the per-CPU time idle statistics counters
|
|
*/
|
|
static void
|
|
update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
|
|
{
|
|
ktime_t delta;
|
|
|
|
if (ts->idle_active) {
|
|
delta = ktime_sub(now, ts->idle_entrytime);
|
|
if (nr_iowait_cpu(cpu) > 0)
|
|
ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
|
|
else
|
|
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
|
|
ts->idle_entrytime = now;
|
|
}
|
|
|
|
if (last_update_time)
|
|
*last_update_time = ktime_to_us(now);
|
|
|
|
}
|
|
|
|
static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
|
|
{
|
|
update_ts_time_stats(smp_processor_id(), ts, now, NULL);
|
|
ts->idle_active = 0;
|
|
|
|
sched_clock_idle_wakeup_event(0);
|
|
}
|
|
|
|
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 cumulative idle time (since boot) for a given
|
|
* CPU, in microseconds.
|
|
*
|
|
* This time is measured via accounting rather than sampling,
|
|
* and is as accurate as ktime_get() is.
|
|
*
|
|
* This function returns -1 if NOHZ is not enabled.
|
|
*/
|
|
u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
|
|
{
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
ktime_t now, idle;
|
|
|
|
if (!tick_nohz_active)
|
|
return -1;
|
|
|
|
now = ktime_get();
|
|
if (last_update_time) {
|
|
update_ts_time_stats(cpu, ts, now, last_update_time);
|
|
idle = ts->idle_sleeptime;
|
|
} else {
|
|
if (ts->idle_active && !nr_iowait_cpu(cpu)) {
|
|
ktime_t delta = ktime_sub(now, ts->idle_entrytime);
|
|
|
|
idle = ktime_add(ts->idle_sleeptime, delta);
|
|
} else {
|
|
idle = ts->idle_sleeptime;
|
|
}
|
|
}
|
|
|
|
return ktime_to_us(idle);
|
|
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
|
|
|
|
/**
|
|
* get_cpu_iowait_time_us - get the total iowait time of a CPU
|
|
* @cpu: CPU number to query
|
|
* @last_update_time: variable to store update time in. Do not update
|
|
* counters if NULL.
|
|
*
|
|
* Return the cumulative iowait time (since boot) for a given
|
|
* CPU, in microseconds.
|
|
*
|
|
* This time is measured via accounting rather than sampling,
|
|
* and is as accurate as ktime_get() is.
|
|
*
|
|
* This function returns -1 if NOHZ is not enabled.
|
|
*/
|
|
u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
|
|
{
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
ktime_t now, iowait;
|
|
|
|
if (!tick_nohz_active)
|
|
return -1;
|
|
|
|
now = ktime_get();
|
|
if (last_update_time) {
|
|
update_ts_time_stats(cpu, ts, now, last_update_time);
|
|
iowait = ts->iowait_sleeptime;
|
|
} else {
|
|
if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
|
|
ktime_t delta = ktime_sub(now, ts->idle_entrytime);
|
|
|
|
iowait = ktime_add(ts->iowait_sleeptime, delta);
|
|
} else {
|
|
iowait = ts->iowait_sleeptime;
|
|
}
|
|
}
|
|
|
|
return ktime_to_us(iowait);
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
|
|
|
|
static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
|
|
{
|
|
hrtimer_cancel(&ts->sched_timer);
|
|
hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
|
|
|
|
/* Forward the time to expire in the future */
|
|
hrtimer_forward(&ts->sched_timer, now, tick_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;
|
|
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
|
|
* force prod the timer.
|
|
*/
|
|
delta = next_tick - basemono;
|
|
if (delta <= (u64)TICK_NSEC) {
|
|
tick = 0;
|
|
|
|
/*
|
|
* Tell the timer code that the base is not idle, i.e. undo
|
|
* the effect of get_next_timer_interrupt():
|
|
*/
|
|
timer_clear_idle();
|
|
/*
|
|
* We've not stopped the tick yet, and there's a timer in the
|
|
* next period, so no point in stopping it either, bail.
|
|
*/
|
|
if (!ts->tick_stopped)
|
|
goto out;
|
|
|
|
/*
|
|
* If, OTOH, we did stop it, but there's a pending (expired)
|
|
* timer reprogram the timer hardware to fire now.
|
|
*
|
|
* We will not restart the tick proper, just prod the timer
|
|
* hardware into firing an interrupt to process the pending
|
|
* timers. Just like tick_irq_exit() will not restart the tick
|
|
* for 'normal' interrupts.
|
|
*
|
|
* Only once we exit the idle loop will we re-enable the tick,
|
|
* see tick_nohz_idle_exit().
|
|
*/
|
|
if (delta == 0) {
|
|
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_deferment value.
|
|
* Otherwise we can sleep as long as we want.
|
|
*/
|
|
delta = timekeeping_max_deferment();
|
|
if (cpu == tick_do_timer_cpu) {
|
|
tick_do_timer_cpu = TICK_DO_TIMER_NONE;
|
|
ts->do_timer_last = 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 = expires;
|
|
|
|
/* Skip reprogram of event if its not changed */
|
|
if (ts->tick_stopped && (expires == dev->next_event))
|
|
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();
|
|
cpu_load_update_nohz_start();
|
|
|
|
ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
|
|
ts->tick_stopped = 1;
|
|
trace_tick_stop(1, TICK_DEP_MASK_NONE);
|
|
}
|
|
|
|
/*
|
|
* 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_restart_sched_tick(struct tick_sched *ts, ktime_t now)
|
|
{
|
|
/* Update jiffies first */
|
|
tick_do_update_jiffies64(now);
|
|
cpu_load_update_nohz_stop();
|
|
|
|
/*
|
|
* Clear the timer idle flag, so we avoid IPIs on remote queueing and
|
|
* the clock forward checks in the enqueue path:
|
|
*/
|
|
timer_clear_idle();
|
|
|
|
calc_load_exit_idle();
|
|
touch_softlockup_watchdog_sched();
|
|
/*
|
|
* 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_full_update_tick(struct tick_sched *ts)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
int cpu = smp_processor_id();
|
|
|
|
if (!tick_nohz_full_cpu(cpu))
|
|
return;
|
|
|
|
if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
|
|
return;
|
|
|
|
if (can_stop_full_tick(cpu, ts))
|
|
tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
|
|
else if (ts->tick_stopped)
|
|
tick_nohz_restart_sched_tick(ts, ktime_get());
|
|
#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 = 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 > 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_update_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;
|
|
}
|
|
|
|
/**
|
|
* tick_nohz_get_idle_calls - return the current idle calls counter value
|
|
*
|
|
* Called from the schedutil frequency scaling governor in scheduler context.
|
|
*/
|
|
unsigned long tick_nohz_get_idle_calls(void)
|
|
{
|
|
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
|
|
|
|
return ts->idle_calls;
|
|
}
|
|
|
|
static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
|
|
{
|
|
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
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|
unsigned long ticks;
|
|
|
|
if (vtime_accounting_cpu_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 = 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_set_expires(&ts->sched_timer, next);
|
|
hrtimer_forward_now(&ts->sched_timer, tick_period);
|
|
tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
|
|
tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
|
|
}
|
|
|
|
static inline void tick_nohz_irq_enter(void)
|
|
{
|
|
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
|
|
ktime_t now;
|
|
|
|
if (!ts->idle_active && !ts->tick_stopped)
|
|
return;
|
|
now = ktime_get();
|
|
if (ts->idle_active)
|
|
tick_nohz_stop_idle(ts, now);
|
|
if (ts->tick_stopped)
|
|
tick_nohz_update_jiffies(now);
|
|
}
|
|
|
|
#else
|
|
|
|
static inline void tick_nohz_switch_to_nohz(void) { }
|
|
static inline void tick_nohz_irq_enter(void) { }
|
|
static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
|
|
|
|
#endif /* CONFIG_NO_HZ_COMMON */
|
|
|
|
/*
|
|
* Called from irq_enter to notify about the possible interruption of idle()
|
|
*/
|
|
void tick_irq_enter(void)
|
|
{
|
|
tick_check_oneshot_broadcast_this_cpu();
|
|
tick_nohz_irq_enter();
|
|
}
|
|
|
|
/*
|
|
* High resolution timer specific code
|
|
*/
|
|
#ifdef CONFIG_HIGH_RES_TIMERS
|
|
/*
|
|
* We rearm the timer until we get disabled by the idle code.
|
|
* Called with interrupts disabled.
|
|
*/
|
|
static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
|
|
{
|
|
struct tick_sched *ts =
|
|
container_of(timer, struct tick_sched, sched_timer);
|
|
struct pt_regs *regs = get_irq_regs();
|
|
ktime_t now = ktime_get();
|
|
|
|
tick_sched_do_timer(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;
|
|
}
|