mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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534c97b095
Pull 'full dynticks' support from Ingo Molnar: "This tree from Frederic Weisbecker adds a new, (exciting! :-) core kernel feature to the timer and scheduler subsystems: 'full dynticks', or CONFIG_NO_HZ_FULL=y. This feature extends the nohz variable-size timer tick feature from idle to busy CPUs (running at most one task) as well, potentially reducing the number of timer interrupts significantly. This feature got motivated by real-time folks and the -rt tree, but the general utility and motivation of full-dynticks runs wider than that: - HPC workloads get faster: CPUs running a single task should be able to utilize a maximum amount of CPU power. A periodic timer tick at HZ=1000 can cause a constant overhead of up to 1.0%. This feature removes that overhead - and speeds up the system by 0.5%-1.0% on typical distro configs even on modern systems. - Real-time workload latency reduction: CPUs running critical tasks should experience as little jitter as possible. The last remaining source of kernel-related jitter was the periodic timer tick. - A single task executing on a CPU is a pretty common situation, especially with an increasing number of cores/CPUs, so this feature helps desktop and mobile workloads as well. The cost of the feature is mainly related to increased timer reprogramming overhead when a CPU switches its tick period, and thus slightly longer to-idle and from-idle latency. Configuration-wise a third mode of operation is added to the existing two NOHZ kconfig modes: - CONFIG_HZ_PERIODIC: [formerly !CONFIG_NO_HZ], now explicitly named as a config option. This is the traditional Linux periodic tick design: there's a HZ tick going on all the time, regardless of whether a CPU is idle or not. - CONFIG_NO_HZ_IDLE: [formerly CONFIG_NO_HZ=y], this turns off the periodic tick when a CPU enters idle mode. - CONFIG_NO_HZ_FULL: this new mode, in addition to turning off the tick when a CPU is idle, also slows the tick down to 1 Hz (one timer interrupt per second) when only a single task is running on a CPU. The .config behavior is compatible: existing !CONFIG_NO_HZ and CONFIG_NO_HZ=y settings get translated to the new values, without the user having to configure anything. CONFIG_NO_HZ_FULL is turned off by default. This feature is based on a lot of infrastructure work that has been steadily going upstream in the last 2-3 cycles: related RCU support and non-periodic cputime support in particular is upstream already. This tree adds the final pieces and activates the feature. The pull request is marked RFC because: - it's marked 64-bit only at the moment - the 32-bit support patch is small but did not get ready in time. - it has a number of fresh commits that came in after the merge window. The overwhelming majority of commits are from before the merge window, but still some aspects of the tree are fresh and so I marked it RFC. - it's a pretty wide-reaching feature with lots of effects - and while the components have been in testing for some time, the full combination is still not very widely used. That it's default-off should reduce its regression abilities and obviously there are no known regressions with CONFIG_NO_HZ_FULL=y enabled either. - the feature is not completely idempotent: there is no 100% equivalent replacement for a periodic scheduler/timer tick. In particular there's ongoing work to map out and reduce its effects on scheduler load-balancing and statistics. This should not impact correctness though, there are no known regressions related to this feature at this point. - it's a pretty ambitious feature that with time will likely be enabled by most Linux distros, and we'd like you to make input on its design/implementation, if you dislike some aspect we missed. Without flaming us to crisp! :-) Future plans: - there's ongoing work to reduce 1Hz to 0Hz, to essentially shut off the periodic tick altogether when there's a single busy task on a CPU. We'd first like 1 Hz to be exposed more widely before we go for the 0 Hz target though. - once we reach 0 Hz we can remove the periodic tick assumption from nr_running>=2 as well, by essentially interrupting busy tasks only as frequently as the sched_latency constraints require us to do - once every 4-40 msecs, depending on nr_running. I am personally leaning towards biting the bullet and doing this in v3.10, like the -rt tree this effort has been going on for too long - but the final word is up to you as usual. More technical details can be found in Documentation/timers/NO_HZ.txt" * 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits) sched: Keep at least 1 tick per second for active dynticks tasks rcu: Fix full dynticks' dependency on wide RCU nocb mode nohz: Protect smp_processor_id() in tick_nohz_task_switch() nohz_full: Add documentation. cputime_nsecs: use math64.h for nsec resolution conversion helpers nohz: Select VIRT_CPU_ACCOUNTING_GEN from full dynticks config nohz: Reduce overhead under high-freq idling patterns nohz: Remove full dynticks' superfluous dependency on RCU tree nohz: Fix unavailable tick_stop tracepoint in dynticks idle nohz: Add basic tracing nohz: Select wide RCU nocb for full dynticks nohz: Disable the tick when irq resume in full dynticks CPU nohz: Re-evaluate the tick for the new task after a context switch nohz: Prepare to stop the tick on irq exit nohz: Implement full dynticks kick nohz: Re-evaluate the tick from the scheduler IPI sched: New helper to prevent from stopping the tick in full dynticks sched: Kick full dynticks CPU that have more than one task enqueued. perf: New helper to prevent full dynticks CPUs from stopping tick perf: Kick full dynticks CPU if events rotation is needed ...
1223 lines
30 KiB
C
1223 lines
30 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 <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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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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}
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write_sequnlock(&jiffies_lock);
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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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static cpumask_var_t nohz_full_mask;
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bool have_nohz_full_mask;
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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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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 = &__get_cpu_var(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 the current 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(void)
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{
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if (tick_nohz_full_cpu(smp_processor_id()))
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irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
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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 (!have_nohz_full_mask)
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return;
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preempt_disable();
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smp_call_function_many(nohz_full_mask,
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nohz_full_kick_ipi, NULL, false);
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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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int tick_nohz_full_cpu(int cpu)
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{
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if (!have_nohz_full_mask)
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return 0;
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return cpumask_test_cpu(cpu, nohz_full_mask);
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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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int cpu;
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alloc_bootmem_cpumask_var(&nohz_full_mask);
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if (cpulist_parse(str, nohz_full_mask) < 0) {
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pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
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return 1;
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}
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cpu = smp_processor_id();
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if (cpumask_test_cpu(cpu, 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, nohz_full_mask);
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}
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have_nohz_full_mask = 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 __cpuinit 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 (have_nohz_full_mask && tick_do_timer_cpu == cpu)
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return -EINVAL;
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break;
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}
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return NOTIFY_OK;
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}
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/*
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* Worst case string length in chunks of CPU range seems 2 steps
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* separations: 0,2,4,6,...
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* This is NR_CPUS + sizeof('\0')
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*/
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static char __initdata nohz_full_buf[NR_CPUS + 1];
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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(&nohz_full_mask, GFP_KERNEL)) {
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pr_err("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(nohz_full_mask);
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cpumask_clear_cpu(smp_processor_id(), nohz_full_mask);
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have_nohz_full_mask = 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 (!have_nohz_full_mask) {
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if (tick_nohz_init_all() < 0)
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return;
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}
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cpu_notifier(tick_nohz_cpu_down_callback, 0);
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/* Make sure full dynticks CPU are also RCU nocbs */
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for_each_cpu(cpu, nohz_full_mask) {
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if (!rcu_is_nocb_cpu(cpu)) {
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pr_warning("NO_HZ: CPU %d is not RCU nocb: "
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"cleared from nohz_full range", cpu);
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cpumask_clear_cpu(cpu, nohz_full_mask);
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}
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}
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cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask);
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pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
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}
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#else
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#define have_nohz_full_mask (0)
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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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int tick_nohz_enabled __read_mostly = 1;
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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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/**
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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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int cpu = smp_processor_id();
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struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
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unsigned long flags;
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ts->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);
|
|
ts->idle_entrytime = now;
|
|
}
|
|
|
|
if (last_update_time)
|
|
*last_update_time = ktime_to_us(now);
|
|
|
|
}
|
|
|
|
static void tick_nohz_stop_idle(int cpu, ktime_t now)
|
|
{
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
|
|
update_ts_time_stats(cpu, ts, now, NULL);
|
|
ts->idle_active = 0;
|
|
|
|
sched_clock_idle_wakeup_event(0);
|
|
}
|
|
|
|
static ktime_t tick_nohz_start_idle(int cpu, struct tick_sched *ts)
|
|
{
|
|
ktime_t now = ktime_get();
|
|
|
|
ts->idle_entrytime = now;
|
|
ts->idle_active = 1;
|
|
sched_clock_idle_sleep_event();
|
|
return now;
|
|
}
|
|
|
|
/**
|
|
* get_cpu_idle_time_us - get the total idle time of a cpu
|
|
* @cpu: CPU number to query
|
|
* @last_update_time: variable to store update time in. Do not update
|
|
* counters if NULL.
|
|
*
|
|
* Return the cummulative idle time (since boot) for a given
|
|
* CPU, in microseconds.
|
|
*
|
|
* This time is measured via accounting rather than sampling,
|
|
* and is as accurate as ktime_get() is.
|
|
*
|
|
* This function returns -1 if NOHZ is not enabled.
|
|
*/
|
|
u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
|
|
{
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
ktime_t now, idle;
|
|
|
|
if (!tick_nohz_enabled)
|
|
return -1;
|
|
|
|
now = ktime_get();
|
|
if (last_update_time) {
|
|
update_ts_time_stats(cpu, ts, now, last_update_time);
|
|
idle = ts->idle_sleeptime;
|
|
} else {
|
|
if (ts->idle_active && !nr_iowait_cpu(cpu)) {
|
|
ktime_t delta = ktime_sub(now, ts->idle_entrytime);
|
|
|
|
idle = ktime_add(ts->idle_sleeptime, delta);
|
|
} else {
|
|
idle = ts->idle_sleeptime;
|
|
}
|
|
}
|
|
|
|
return ktime_to_us(idle);
|
|
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
|
|
|
|
/**
|
|
* get_cpu_iowait_time_us - get the total iowait time of a cpu
|
|
* @cpu: CPU number to query
|
|
* @last_update_time: variable to store update time in. Do not update
|
|
* counters if NULL.
|
|
*
|
|
* Return the cummulative iowait time (since boot) for a given
|
|
* CPU, in microseconds.
|
|
*
|
|
* This time is measured via accounting rather than sampling,
|
|
* and is as accurate as ktime_get() is.
|
|
*
|
|
* This function returns -1 if NOHZ is not enabled.
|
|
*/
|
|
u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
|
|
{
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
ktime_t now, iowait;
|
|
|
|
if (!tick_nohz_enabled)
|
|
return -1;
|
|
|
|
now = ktime_get();
|
|
if (last_update_time) {
|
|
update_ts_time_stats(cpu, ts, now, last_update_time);
|
|
iowait = ts->iowait_sleeptime;
|
|
} else {
|
|
if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
|
|
ktime_t delta = ktime_sub(now, ts->idle_entrytime);
|
|
|
|
iowait = ktime_add(ts->iowait_sleeptime, delta);
|
|
} else {
|
|
iowait = ts->iowait_sleeptime;
|
|
}
|
|
}
|
|
|
|
return ktime_to_us(iowait);
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
|
|
|
|
static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
|
|
ktime_t now, int cpu)
|
|
{
|
|
unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
|
|
ktime_t last_update, expires, ret = { .tv64 = 0 };
|
|
unsigned long rcu_delta_jiffies;
|
|
struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
|
|
u64 time_delta;
|
|
|
|
/* Read jiffies and the time when jiffies were updated last */
|
|
do {
|
|
seq = read_seqbegin(&jiffies_lock);
|
|
last_update = last_jiffies_update;
|
|
last_jiffies = jiffies;
|
|
time_delta = timekeeping_max_deferment();
|
|
} while (read_seqretry(&jiffies_lock, seq));
|
|
|
|
if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
|
|
arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
|
|
next_jiffies = last_jiffies + 1;
|
|
delta_jiffies = 1;
|
|
} else {
|
|
/* Get the next timer wheel timer */
|
|
next_jiffies = get_next_timer_interrupt(last_jiffies);
|
|
delta_jiffies = next_jiffies - last_jiffies;
|
|
if (rcu_delta_jiffies < delta_jiffies) {
|
|
next_jiffies = last_jiffies + rcu_delta_jiffies;
|
|
delta_jiffies = rcu_delta_jiffies;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Do not stop the tick, if we are only one off (or less)
|
|
* or if the cpu is required for RCU:
|
|
*/
|
|
if (!ts->tick_stopped && delta_jiffies <= 1)
|
|
goto out;
|
|
|
|
/* Schedule the tick, if we are at least one jiffie off */
|
|
if ((long)delta_jiffies >= 1) {
|
|
|
|
/*
|
|
* If this cpu is the one which updates jiffies, then
|
|
* give up the assignment and let it be taken by the
|
|
* cpu which runs the tick timer next, which might be
|
|
* this cpu as well. If we don't drop this here the
|
|
* jiffies might be stale and do_timer() never
|
|
* invoked. Keep track of the fact that it was the one
|
|
* which had the do_timer() duty last. If this cpu is
|
|
* the one which had the do_timer() duty last, we
|
|
* limit the sleep time to the timekeeping
|
|
* max_deferement value which we retrieved
|
|
* above. Otherwise we can sleep as long as we want.
|
|
*/
|
|
if (cpu == tick_do_timer_cpu) {
|
|
tick_do_timer_cpu = TICK_DO_TIMER_NONE;
|
|
ts->do_timer_last = 1;
|
|
} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
|
|
time_delta = KTIME_MAX;
|
|
ts->do_timer_last = 0;
|
|
} else if (!ts->do_timer_last) {
|
|
time_delta = KTIME_MAX;
|
|
}
|
|
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (!ts->inidle) {
|
|
time_delta = min(time_delta,
|
|
scheduler_tick_max_deferment());
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* calculate the expiry time for the next timer wheel
|
|
* timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
|
|
* that there is no timer pending or at least extremely
|
|
* far into the future (12 days for HZ=1000). In this
|
|
* case we set the expiry to the end of time.
|
|
*/
|
|
if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
|
|
/*
|
|
* Calculate the time delta for the next timer event.
|
|
* If the time delta exceeds the maximum time delta
|
|
* permitted by the current clocksource then adjust
|
|
* the time delta accordingly to ensure the
|
|
* clocksource does not wrap.
|
|
*/
|
|
time_delta = min_t(u64, time_delta,
|
|
tick_period.tv64 * delta_jiffies);
|
|
}
|
|
|
|
if (time_delta < KTIME_MAX)
|
|
expires = ktime_add_ns(last_update, time_delta);
|
|
else
|
|
expires.tv64 = KTIME_MAX;
|
|
|
|
/* Skip reprogram of event if its not changed */
|
|
if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
|
|
goto out;
|
|
|
|
ret = expires;
|
|
|
|
/*
|
|
* nohz_stop_sched_tick can be called several times before
|
|
* the nohz_restart_sched_tick is called. This happens when
|
|
* interrupts arrive which do not cause a reschedule. In the
|
|
* first call we save the current tick time, so we can restart
|
|
* the scheduler tick in nohz_restart_sched_tick.
|
|
*/
|
|
if (!ts->tick_stopped) {
|
|
nohz_balance_enter_idle(cpu);
|
|
calc_load_enter_idle();
|
|
|
|
ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
|
|
ts->tick_stopped = 1;
|
|
trace_tick_stop(1, " ");
|
|
}
|
|
|
|
/*
|
|
* If the expiration time == KTIME_MAX, then
|
|
* in this case we simply stop the tick timer.
|
|
*/
|
|
if (unlikely(expires.tv64 == KTIME_MAX)) {
|
|
if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
|
|
hrtimer_cancel(&ts->sched_timer);
|
|
goto out;
|
|
}
|
|
|
|
if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
|
|
hrtimer_start(&ts->sched_timer, expires,
|
|
HRTIMER_MODE_ABS_PINNED);
|
|
/* Check, if the timer was already in the past */
|
|
if (hrtimer_active(&ts->sched_timer))
|
|
goto out;
|
|
} else if (!tick_program_event(expires, 0))
|
|
goto out;
|
|
/*
|
|
* We are past the event already. So we crossed a
|
|
* jiffie boundary. Update jiffies and raise the
|
|
* softirq.
|
|
*/
|
|
tick_do_update_jiffies64(ktime_get());
|
|
}
|
|
raise_softirq_irqoff(TIMER_SOFTIRQ);
|
|
out:
|
|
ts->next_jiffies = next_jiffies;
|
|
ts->last_jiffies = last_jiffies;
|
|
ts->sleep_length = ktime_sub(dev->next_event, now);
|
|
|
|
return ret;
|
|
}
|
|
|
|
static 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;
|
|
}
|
|
|
|
if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
|
|
return false;
|
|
|
|
if (need_resched())
|
|
return false;
|
|
|
|
if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
|
|
static int ratelimit;
|
|
|
|
if (ratelimit < 10 &&
|
|
(local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
|
|
pr_warn("NOHZ: local_softirq_pending %02x\n",
|
|
(unsigned int) local_softirq_pending());
|
|
ratelimit++;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
if (have_nohz_full_mask) {
|
|
/*
|
|
* 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(cpu, ts);
|
|
|
|
if (can_stop_idle_tick(cpu, ts)) {
|
|
int was_stopped = ts->tick_stopped;
|
|
|
|
ts->idle_calls++;
|
|
|
|
expires = tick_nohz_stop_sched_tick(ts, now, cpu);
|
|
if (expires.tv64 > 0LL) {
|
|
ts->idle_sleeps++;
|
|
ts->idle_expires = expires;
|
|
}
|
|
|
|
if (!was_stopped && ts->tick_stopped)
|
|
ts->idle_jiffies = ts->last_jiffies;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* tick_nohz_idle_enter - stop the idle tick from the idle task
|
|
*
|
|
* When the next event is more than a tick into the future, stop the idle tick
|
|
* Called when we start the idle loop.
|
|
*
|
|
* The arch is responsible of calling:
|
|
*
|
|
* - rcu_idle_enter() after its last use of RCU before the CPU is put
|
|
* to sleep.
|
|
* - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
|
|
*/
|
|
void tick_nohz_idle_enter(void)
|
|
{
|
|
struct tick_sched *ts;
|
|
|
|
WARN_ON_ONCE(irqs_disabled());
|
|
|
|
/*
|
|
* Update the idle state in the scheduler domain hierarchy
|
|
* when tick_nohz_stop_sched_tick() is called from the idle loop.
|
|
* State will be updated to busy during the first busy tick after
|
|
* exiting idle.
|
|
*/
|
|
set_cpu_sd_state_idle();
|
|
|
|
local_irq_disable();
|
|
|
|
ts = &__get_cpu_var(tick_cpu_sched);
|
|
/*
|
|
* set ts->inidle unconditionally. even if the system did not
|
|
* switch to nohz mode the cpu frequency governers rely on the
|
|
* update of the idle time accounting in tick_nohz_start_idle().
|
|
*/
|
|
ts->inidle = 1;
|
|
__tick_nohz_idle_enter(ts);
|
|
|
|
local_irq_enable();
|
|
}
|
|
EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
|
|
|
|
/**
|
|
* tick_nohz_irq_exit - update next tick event from interrupt exit
|
|
*
|
|
* When an interrupt fires while we are idle and it doesn't cause
|
|
* a reschedule, it may still add, modify or delete a timer, enqueue
|
|
* an RCU callback, etc...
|
|
* So we need to re-calculate and reprogram the next tick event.
|
|
*/
|
|
void tick_nohz_irq_exit(void)
|
|
{
|
|
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
|
|
|
|
if (ts->inidle) {
|
|
/* Cancel the timer because CPU already waken up from the C-states*/
|
|
menu_hrtimer_cancel();
|
|
__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 = &__get_cpu_var(tick_cpu_sched);
|
|
|
|
return ts->sleep_length;
|
|
}
|
|
|
|
static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
|
|
{
|
|
hrtimer_cancel(&ts->sched_timer);
|
|
hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
|
|
|
|
while (1) {
|
|
/* Forward the time to expire in the future */
|
|
hrtimer_forward(&ts->sched_timer, now, tick_period);
|
|
|
|
if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
|
|
hrtimer_start_expires(&ts->sched_timer,
|
|
HRTIMER_MODE_ABS_PINNED);
|
|
/* Check, if the timer was already in the past */
|
|
if (hrtimer_active(&ts->sched_timer))
|
|
break;
|
|
} else {
|
|
if (!tick_program_event(
|
|
hrtimer_get_expires(&ts->sched_timer), 0))
|
|
break;
|
|
}
|
|
/* Reread time and update jiffies */
|
|
now = ktime_get();
|
|
tick_do_update_jiffies64(now);
|
|
}
|
|
}
|
|
|
|
static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
|
|
{
|
|
/* Update jiffies first */
|
|
tick_do_update_jiffies64(now);
|
|
update_cpu_load_nohz();
|
|
|
|
calc_load_exit_idle();
|
|
touch_softlockup_watchdog();
|
|
/*
|
|
* Cancel the scheduled timer and restore the tick
|
|
*/
|
|
ts->tick_stopped = 0;
|
|
ts->idle_exittime = now;
|
|
|
|
tick_nohz_restart(ts, now);
|
|
}
|
|
|
|
static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
|
|
{
|
|
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_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)
|
|
{
|
|
int cpu = smp_processor_id();
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
ktime_t now;
|
|
|
|
local_irq_disable();
|
|
|
|
WARN_ON_ONCE(!ts->inidle);
|
|
|
|
ts->inidle = 0;
|
|
|
|
/* Cancel the timer because CPU already waken up from the C-states*/
|
|
menu_hrtimer_cancel();
|
|
if (ts->idle_active || ts->tick_stopped)
|
|
now = ktime_get();
|
|
|
|
if (ts->idle_active)
|
|
tick_nohz_stop_idle(cpu, now);
|
|
|
|
if (ts->tick_stopped) {
|
|
tick_nohz_restart_sched_tick(ts, now);
|
|
tick_nohz_account_idle_ticks(ts);
|
|
}
|
|
|
|
local_irq_enable();
|
|
}
|
|
EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
|
|
|
|
static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
|
|
{
|
|
hrtimer_forward(&ts->sched_timer, now, tick_period);
|
|
return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
|
|
}
|
|
|
|
/*
|
|
* The nohz low res interrupt handler
|
|
*/
|
|
static void tick_nohz_handler(struct clock_event_device *dev)
|
|
{
|
|
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
|
|
struct pt_regs *regs = get_irq_regs();
|
|
ktime_t now = ktime_get();
|
|
|
|
dev->next_event.tv64 = KTIME_MAX;
|
|
|
|
tick_sched_do_timer(now);
|
|
tick_sched_handle(ts, regs);
|
|
|
|
while (tick_nohz_reprogram(ts, now)) {
|
|
now = ktime_get();
|
|
tick_do_update_jiffies64(now);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* tick_nohz_switch_to_nohz - switch to nohz mode
|
|
*/
|
|
static void tick_nohz_switch_to_nohz(void)
|
|
{
|
|
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
|
|
ktime_t next;
|
|
|
|
if (!tick_nohz_enabled)
|
|
return;
|
|
|
|
local_irq_disable();
|
|
if (tick_switch_to_oneshot(tick_nohz_handler)) {
|
|
local_irq_enable();
|
|
return;
|
|
}
|
|
|
|
ts->nohz_mode = NOHZ_MODE_LOWRES;
|
|
|
|
/*
|
|
* Recycle the hrtimer in ts, so we can share the
|
|
* hrtimer_forward with the highres code.
|
|
*/
|
|
hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
|
|
/* Get the next period */
|
|
next = tick_init_jiffy_update();
|
|
|
|
for (;;) {
|
|
hrtimer_set_expires(&ts->sched_timer, next);
|
|
if (!tick_program_event(next, 0))
|
|
break;
|
|
next = ktime_add(next, tick_period);
|
|
}
|
|
local_irq_enable();
|
|
}
|
|
|
|
/*
|
|
* When NOHZ is enabled and the tick is stopped, we need to kick the
|
|
* tick timer from irq_enter() so that the jiffies update is kept
|
|
* alive during long running softirqs. That's ugly as hell, but
|
|
* correctness is key even if we need to fix the offending softirq in
|
|
* the first place.
|
|
*
|
|
* Note, this is different to tick_nohz_restart. We just kick the
|
|
* timer and do not touch the other magic bits which need to be done
|
|
* when idle is left.
|
|
*/
|
|
static void tick_nohz_kick_tick(int cpu, ktime_t now)
|
|
{
|
|
#if 0
|
|
/* Switch back to 2.6.27 behaviour */
|
|
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
ktime_t delta;
|
|
|
|
/*
|
|
* Do not touch the tick device, when the next expiry is either
|
|
* already reached or less/equal than the tick period.
|
|
*/
|
|
delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
|
|
if (delta.tv64 <= tick_period.tv64)
|
|
return;
|
|
|
|
tick_nohz_restart(ts, now);
|
|
#endif
|
|
}
|
|
|
|
static inline void tick_check_nohz(int cpu)
|
|
{
|
|
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
|
|
ktime_t now;
|
|
|
|
if (!ts->idle_active && !ts->tick_stopped)
|
|
return;
|
|
now = ktime_get();
|
|
if (ts->idle_active)
|
|
tick_nohz_stop_idle(cpu, now);
|
|
if (ts->tick_stopped) {
|
|
tick_nohz_update_jiffies(now);
|
|
tick_nohz_kick_tick(cpu, now);
|
|
}
|
|
}
|
|
|
|
#else
|
|
|
|
static inline void tick_nohz_switch_to_nohz(void) { }
|
|
static inline void tick_check_nohz(int cpu) { }
|
|
|
|
#endif /* CONFIG_NO_HZ_COMMON */
|
|
|
|
/*
|
|
* Called from irq_enter to notify about the possible interruption of idle()
|
|
*/
|
|
void tick_check_idle(int cpu)
|
|
{
|
|
tick_check_oneshot_broadcast(cpu);
|
|
tick_check_nohz(cpu);
|
|
}
|
|
|
|
/*
|
|
* High resolution timer specific code
|
|
*/
|
|
#ifdef CONFIG_HIGH_RES_TIMERS
|
|
/*
|
|
* We rearm the timer until we get disabled by the idle code.
|
|
* Called with interrupts disabled.
|
|
*/
|
|
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);
|
|
|
|
hrtimer_forward(timer, now, tick_period);
|
|
|
|
return HRTIMER_RESTART;
|
|
}
|
|
|
|
static int sched_skew_tick;
|
|
|
|
static int __init skew_tick(char *str)
|
|
{
|
|
get_option(&str, &sched_skew_tick);
|
|
|
|
return 0;
|
|
}
|
|
early_param("skew_tick", skew_tick);
|
|
|
|
/**
|
|
* tick_setup_sched_timer - setup the tick emulation timer
|
|
*/
|
|
void tick_setup_sched_timer(void)
|
|
{
|
|
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
|
|
ktime_t now = ktime_get();
|
|
|
|
/*
|
|
* Emulate tick processing via per-CPU hrtimers:
|
|
*/
|
|
hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
|
|
ts->sched_timer.function = tick_sched_timer;
|
|
|
|
/* Get the next period (per cpu) */
|
|
hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
|
|
|
|
/* Offset the tick to avert 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);
|
|
}
|
|
|
|
for (;;) {
|
|
hrtimer_forward(&ts->sched_timer, now, tick_period);
|
|
hrtimer_start_expires(&ts->sched_timer,
|
|
HRTIMER_MODE_ABS_PINNED);
|
|
/* Check, if the timer was already in the past */
|
|
if (hrtimer_active(&ts->sched_timer))
|
|
break;
|
|
now = ktime_get();
|
|
}
|
|
|
|
#ifdef CONFIG_NO_HZ_COMMON
|
|
if (tick_nohz_enabled)
|
|
ts->nohz_mode = NOHZ_MODE_HIGHRES;
|
|
#endif
|
|
}
|
|
#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
|
|
|
|
ts->nohz_mode = NOHZ_MODE_INACTIVE;
|
|
}
|
|
#endif
|
|
|
|
/**
|
|
* Async notification about clocksource changes
|
|
*/
|
|
void tick_clock_notify(void)
|
|
{
|
|
int cpu;
|
|
|
|
for_each_possible_cpu(cpu)
|
|
set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
|
|
}
|
|
|
|
/*
|
|
* Async notification about clock event changes
|
|
*/
|
|
void tick_oneshot_notify(void)
|
|
{
|
|
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
|
|
|
|
set_bit(0, &ts->check_clocks);
|
|
}
|
|
|
|
/**
|
|
* Check, if a change happened, which makes oneshot possible.
|
|
*
|
|
* Called cyclic from the hrtimer softirq (driven by the timer
|
|
* softirq) allow_nohz signals, that we can switch into low-res nohz
|
|
* mode, because high resolution timers are disabled (either compile
|
|
* or runtime).
|
|
*/
|
|
int tick_check_oneshot_change(int allow_nohz)
|
|
{
|
|
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
|
|
|
|
if (!test_and_clear_bit(0, &ts->check_clocks))
|
|
return 0;
|
|
|
|
if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
|
|
return 0;
|
|
|
|
if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
|
|
return 0;
|
|
|
|
if (!allow_nohz)
|
|
return 1;
|
|
|
|
tick_nohz_switch_to_nohz();
|
|
return 0;
|
|
}
|