ladybird/Kernel/TimerQueue.h

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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Function.h>
#include <AK/IntrusiveList.h>
#include <AK/NonnullRefPtr.h>
#include <AK/OwnPtr.h>
#include <AK/RefCounted.h>
#include <AK/Time.h>
Kernel: Introduce the new Time management subsystem This new subsystem includes better abstractions of how time will be handled in the OS. We take advantage of the existing RTC timer to aid in keeping time synchronized. This is standing in contrast to how we handled time-keeping in the kernel, where the PIT was responsible for that function in addition to update the scheduler about ticks. With that new advantage, we can easily change the ticking dynamically and still keep the time synchronized. In the process context, we no longer use a fixed declaration of TICKS_PER_SECOND, but we call the TimeManagement singleton class to provide us the right value. This allows us to use dynamic ticking in the future, a feature known as tickless kernel. The scheduler no longer does by himself the calculation of real time (Unix time), and just calls the TimeManagment singleton class to provide the value. Also, we can use 2 new boot arguments: - the "time" boot argument accpets either the value "modern", or "legacy". If "modern" is specified, the time management subsystem will try to setup HPET. Otherwise, for "legacy" value, the time subsystem will revert to use the PIT & RTC, leaving HPET disabled. If this boot argument is not specified, the default pattern is to try to setup HPET. - the "hpet" boot argumet accepts either the value "periodic" or "nonperiodic". If "periodic" is specified, the HPET will scan for periodic timers, and will assert if none are found. If only one is found, that timer will be assigned for the time-keeping task. If more than one is found, both time-keeping task & scheduler-ticking task will be assigned to periodic timers. If this boot argument is not specified, the default pattern is to try to scan for HPET periodic timers. This boot argument has no effect if HPET is disabled. In hardware context, PIT & RealTimeClock classes are merely inheriting from the HardwareTimer class, and they allow to use the old i8254 (PIT) and RTC devices, managing them via IO ports. By default, the RTC will be programmed to a frequency of 1024Hz. The PIT will be programmed to a frequency close to 1000Hz. About HPET, depending if we need to scan for periodic timers or not, we try to set a frequency close to 1000Hz for the time-keeping timer and scheduler-ticking timer. Also, if possible, we try to enable the Legacy replacement feature of the HPET. This feature if exists, instructs the chipset to disconnect both i8254 (PIT) and RTC. This behavior is observable on QEMU, and was verified against the source code: https://github.com/qemu/qemu/commit/ce967e2f33861b0e17753f97fa4527b5943c94b6 The HPETComparator class is inheriting from HardwareTimer class, and is responsible for an individual HPET comparator, which is essentially a timer. Therefore, it needs to call the singleton HPET class to perform HPET-related operations. The new abstraction of Hardware timers brings an opportunity of more new features in the foreseeable future. For example, we can change the callback function of each hardware timer, thus it makes it possible to swap missions between hardware timers, or to allow to use a hardware timer for other temporary missions (e.g. calibrating the LAPIC timer, measuring the CPU frequency, etc).
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#include <Kernel/Time/TimeManagement.h>
namespace Kernel {
TYPEDEF_DISTINCT_ORDERED_ID(u64, TimerId);
class Timer : public RefCounted<Timer> {
friend class TimerQueue;
public:
void setup(clockid_t clock_id, Time expires, Function<void()>&& callback)
{
VERIFY(!is_queued());
m_clock_id = clock_id;
m_expires = expires;
m_callback = move(callback);
}
~Timer()
{
VERIFY(!is_queued());
}
Time remaining() const;
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private:
TimerId m_id;
clockid_t m_clock_id;
Time m_expires;
Time m_remaining {};
Function<void()> m_callback;
Atomic<bool> m_cancelled { false };
Atomic<bool> m_callback_finished { false };
Atomic<bool> m_in_use { false };
bool operator<(const Timer& rhs) const
{
return m_expires < rhs.m_expires;
}
bool operator>(const Timer& rhs) const
{
return m_expires > rhs.m_expires;
}
bool operator==(const Timer& rhs) const
{
return m_id == rhs.m_id;
}
void clear_cancelled() { return m_cancelled.store(false, AK::memory_order_release); }
bool set_cancelled() { return m_cancelled.exchange(true, AK::memory_order_acq_rel); }
bool is_in_use() { return m_in_use.load(AK::memory_order_acquire); };
void set_in_use() { m_in_use.store(true, AK::memory_order_release); }
void clear_in_use() { return m_in_use.store(false, AK::memory_order_release); }
bool is_callback_finished() const { return m_callback_finished.load(AK::memory_order_acquire); }
void clear_callback_finished() { m_callback_finished.store(false, AK::memory_order_release); }
void set_callback_finished() { m_callback_finished.store(true, AK::memory_order_release); }
Time now(bool) const;
bool is_queued() const { return m_list_node.is_in_list(); }
public:
IntrusiveListNode<Timer> m_list_node;
using List = IntrusiveList<&Timer::m_list_node>;
};
class TimerQueue {
friend class Timer;
public:
TimerQueue();
static TimerQueue& the();
TimerId add_timer(NonnullRefPtr<Timer>&&);
bool add_timer_without_id(NonnullRefPtr<Timer>, clockid_t, const Time&, Function<void()>&&);
bool cancel_timer(Timer& timer, bool* was_in_use = nullptr);
void fire();
private:
struct Queue {
Timer::List list;
Time next_timer_due {};
};
void remove_timer_locked(Queue&, Timer&);
void update_next_timer_due(Queue&);
void add_timer_locked(NonnullRefPtr<Timer>);
Queue& queue_for_timer(Timer& timer)
{
switch (timer.m_clock_id) {
case CLOCK_MONOTONIC:
case CLOCK_MONOTONIC_COARSE:
case CLOCK_MONOTONIC_RAW:
return m_timer_queue_monotonic;
case CLOCK_REALTIME:
case CLOCK_REALTIME_COARSE:
return m_timer_queue_realtime;
default:
VERIFY_NOT_REACHED();
}
}
u64 m_timer_id_count { 0 };
u64 m_ticks_per_second { 0 };
Queue m_timer_queue_monotonic;
Queue m_timer_queue_realtime;
Timer::List m_timers_executing;
};
}