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src/core/hle/kernel/k_scheduler.h

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+// Copyright 2020 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+// This file references various implementation details from Atmosphere, an open-source firmware for
+// the Nintendo Switch. Copyright 2018-2020 Atmosphere-NX.
+
+#pragma once
+
+#include <atomic>
+
+#include "common/common_types.h"
+#include "common/spin_lock.h"
+#include "core/hle/kernel/global_scheduler_context.h"
+#include "core/hle/kernel/k_priority_queue.h"
+#include "core/hle/kernel/k_scheduler_lock.h"
+#include "core/hle/kernel/k_scoped_lock.h"
+
+namespace Common {
+class Fiber;
+}
+
+namespace Core {
+class System;
+}
+
+namespace Kernel {
+
+class KernelCore;
+class Process;
+class SchedulerLock;
+class Thread;
+
+class KScheduler final {
+public:
+    explicit KScheduler(Core::System& system, std::size_t core_id);
+    ~KScheduler();
+
+    /// Reschedules to the next available thread (call after current thread is suspended)
+    void RescheduleCurrentCore();
+
+    /// Reschedules cores pending reschedule, to be called on EnableScheduling.
+    static void RescheduleCores(KernelCore& kernel, u64 cores_pending_reschedule,
+                                Core::EmuThreadHandle global_thread);
+
+    /// The next two are for SingleCore Only.
+    /// Unload current thread before preempting core.
+    void Unload(Thread* thread);
+
+    /// Reload current thread after core preemption.
+    void Reload(Thread* thread);
+
+    /// Gets the current running thread
+    [[nodiscard]] Thread* GetCurrentThread() const;
+
+    /// Gets the timestamp for the last context switch in ticks.
+    [[nodiscard]] u64 GetLastContextSwitchTicks() const;
+
+    [[nodiscard]] bool ContextSwitchPending() const {
+        return state.needs_scheduling.load(std::memory_order_relaxed);
+    }
+
+    void Initialize();
+
+    void OnThreadStart();
+
+    [[nodiscard]] std::shared_ptr<Common::Fiber>& ControlContext() {
+        return switch_fiber;
+    }
+
+    [[nodiscard]] const std::shared_ptr<Common::Fiber>& ControlContext() const {
+        return switch_fiber;
+    }
+
+    [[nodiscard]] u64 UpdateHighestPriorityThread(Thread* highest_thread);
+
+    /**
+     * Takes a thread and moves it to the back of the it's priority list.
+     *
+     * @note This operation can be redundant and no scheduling is changed if marked as so.
+     */
+    void YieldWithoutCoreMigration();
+
+    /**
+     * Takes a thread and moves it to the back of the it's priority list.
+     * Afterwards, tries to pick a suggested thread from the suggested queue that has worse time or
+     * a better priority than the next thread in the core.
+     *
+     * @note This operation can be redundant and no scheduling is changed if marked as so.
+     */
+    void YieldWithCoreMigration();
+
+    /**
+     * Takes a thread and moves it out of the scheduling queue.
+     * and into the suggested queue. If no thread can be scheduled afterwards in that core,
+     * a suggested thread is obtained instead.
+     *
+     * @note This operation can be redundant and no scheduling is changed if marked as so.
+     */
+    void YieldToAnyThread();
+
+    /// Notify the scheduler a thread's status has changed.
+    static void OnThreadStateChanged(KernelCore& kernel, Thread* thread, u32 old_state);
+
+    /// Notify the scheduler a thread's priority has changed.
+    static void OnThreadPriorityChanged(KernelCore& kernel, Thread* thread, Thread* current_thread,
+                                        u32 old_priority);
+
+    /// Notify the scheduler a thread's core and/or affinity mask has changed.
+    static void OnThreadAffinityMaskChanged(KernelCore& kernel, Thread* thread,
+                                            const KAffinityMask& old_affinity, s32 old_core);
+
+    static bool CanSchedule(KernelCore& kernel);
+    static bool IsSchedulerUpdateNeeded(const KernelCore& kernel);
+    static void SetSchedulerUpdateNeeded(KernelCore& kernel);
+    static void ClearSchedulerUpdateNeeded(KernelCore& kernel);
+    static void DisableScheduling(KernelCore& kernel);
+    static void EnableScheduling(KernelCore& kernel, u64 cores_needing_scheduling,
+                                 Core::EmuThreadHandle global_thread);
+    [[nodiscard]] static u64 UpdateHighestPriorityThreads(KernelCore& kernel);
+
+private:
+    friend class GlobalSchedulerContext;
+
+    /**
+     * Takes care of selecting the new scheduled threads in three steps:
+     *
+     * 1. First a thread is selected from the top of the priority queue. If no thread
+     *    is obtained then we move to step two, else we are done.
+     *
+     * 2. Second we try to get a suggested thread that's not assigned to any core or
+     *    that is not the top thread in that core.
+     *
+     * 3. Third is no suggested thread is found, we do a second pass and pick a running
+     *    thread in another core and swap it with its current thread.
+     *
+     * returns the cores needing scheduling.
+     */
+    [[nodiscard]] static u64 UpdateHighestPriorityThreadsImpl(KernelCore& kernel);
+
+    [[nodiscard]] static KSchedulerPriorityQueue& GetPriorityQueue(KernelCore& kernel);
+
+    void RotateScheduledQueue(s32 core_id, s32 priority);
+
+    void Schedule() {
+        ASSERT(GetCurrentThread()->GetDisableDispatchCount() == 1);
+        this->ScheduleImpl();
+    }
+
+    /// Switches the CPU's active thread context to that of the specified thread
+    void ScheduleImpl();
+
+    /// When a thread wakes up, it must run this through it's new scheduler
+    void SwitchContextStep2();
+
+    /**
+     * Called on every context switch to update the internal timestamp
+     * This also updates the running time ticks for the given thread and
+     * process using the following difference:
+     *
+     * ticks += most_recent_ticks - last_context_switch_ticks
+     *
+     * The internal tick timestamp for the scheduler is simply the
+     * most recent tick count retrieved. No special arithmetic is
+     * applied to it.
+     */
+    void UpdateLastContextSwitchTime(Thread* thread, Process* process);
+
+    static void OnSwitch(void* this_scheduler);
+    void SwitchToCurrent();
+
+    Thread* current_thread{};
+    Thread* idle_thread{};
+
+    std::shared_ptr<Common::Fiber> switch_fiber{};
+
+    struct SchedulingState {
+        std::atomic<bool> needs_scheduling;
+        bool interrupt_task_thread_runnable{};
+        bool should_count_idle{};
+        u64 idle_count{};
+        Thread* highest_priority_thread{};
+        void* idle_thread_stack{};
+    };
+
+    SchedulingState state;
+
+    Core::System& system;
+    u64 last_context_switch_time{};
+    const std::size_t core_id;
+
+    Common::SpinLock guard{};
+};
+
+class KScopedSchedulerLock : KScopedLock<GlobalSchedulerContext::LockType> {
+public:
+    explicit KScopedSchedulerLock(KernelCore& kernel);
+    ~KScopedSchedulerLock();
+};
+
+} // namespace Kernel