// Copyright 2018 yuzu emulator team
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
//
// SelectThreads, Yield functions originally by TuxSH.
// licensed under GPLv2 or later under exception provided by the author.
#include <algorithm>
#include <set>
#include <unordered_set>
#include <utility>
#include "common/assert.h"
#include "common/logging/log.h"
#include "core/arm/arm_interface.h"
#include "core/core.h"
#include "core/core_cpu.h"
#include "core/core_timing.h"
#include "core/hle/kernel/kernel.h"
#include "core/hle/kernel/process.h"
#include "core/hle/kernel/scheduler.h"
namespace Kernel {
GlobalScheduler::GlobalScheduler(Core::System& system) : system{system} {
reselection_pending = false;
}
void GlobalScheduler::AddThread(SharedPtr<Thread> thread) {
thread_list.push_back(std::move(thread));
}
void GlobalScheduler::RemoveThread(const Thread* thread) {
thread_list.erase(std::remove(thread_list.begin(), thread_list.end(), thread),
thread_list.end());
}
/*
* UnloadThread selects a core and forces it to unload its current thread's context
*/
void GlobalScheduler::UnloadThread(s32 core) {
Scheduler& sched = system.Scheduler(core);
sched.UnloadThread();
}
/*
* SelectThread takes care of selecting the new scheduled thread.
* It does it in 3 steps:
* - 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.
* - 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.
* - 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.
*/
void GlobalScheduler::SelectThread(u32 core) {
const auto update_thread = [](Thread* thread, Scheduler& sched) {
if (thread != sched.selected_thread) {
if (thread == nullptr) {
++sched.idle_selection_count;
}
sched.selected_thread = thread;
}
sched.context_switch_pending = sched.selected_thread != sched.current_thread;
std::atomic_thread_fence(std::memory_order_seq_cst);
};
Scheduler& sched = system.Scheduler(core);
Thread* current_thread = nullptr;
// Step 1: Get top thread in schedule queue.
current_thread = scheduled_queue[core].empty() ? nullptr : scheduled_queue[core].front();
if (current_thread) {
update_thread(current_thread, sched);
return;
}
// Step 2: Try selecting a suggested thread.
Thread* winner = nullptr;
std::set<s32> sug_cores;
for (auto thread : suggested_queue[core]) {
s32 this_core = thread->GetProcessorID();
Thread* thread_on_core = nullptr;
if (this_core >= 0) {
thread_on_core = scheduled_queue[this_core].front();
}
if (this_core < 0 || thread != thread_on_core) {
winner = thread;
break;
}
sug_cores.insert(this_core);
}
// if we got a suggested thread, select it, else do a second pass.
if (winner && winner->GetPriority() > 2) {
if (winner->IsRunning()) {
UnloadThread(winner->GetProcessorID());
}
TransferToCore(winner->GetPriority(), core, winner);
update_thread(winner, sched);
return;
}
// Step 3: Select a suggested thread from another core
for (auto& src_core : sug_cores) {
auto it = scheduled_queue[src_core].begin();
it++;
if (it != scheduled_queue[src_core].end()) {
Thread* thread_on_core = scheduled_queue[src_core].front();
Thread* to_change = *it;
if (thread_on_core->IsRunning() || to_change->IsRunning()) {
UnloadThread(src_core);
}
TransferToCore(thread_on_core->GetPriority(), core, thread_on_core);
current_thread = thread_on_core;
break;
}
}
update_thread(current_thread, sched);
}
/*
* YieldThread takes a thread and moves it to the back of the it's priority list
* This operation can be redundant and no scheduling is changed if marked as so.
*/
bool GlobalScheduler::YieldThread(Thread* yielding_thread) {
// Note: caller should use critical section, etc.
const u32 core_id = static_cast<u32>(yielding_thread->GetProcessorID());
const u32 priority = yielding_thread->GetPriority();
// Yield the thread
ASSERT_MSG(yielding_thread == scheduled_queue[core_id].front(priority),
"Thread yielding without being in front");
scheduled_queue[core_id].yield(priority);
Thread* winner = scheduled_queue[core_id].front(priority);
return AskForReselectionOrMarkRedundant(yielding_thread, winner);
}
/*
* YieldThreadAndBalanceLoad 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.
* This operation can be redundant and no scheduling is changed if marked as so.
*/
bool GlobalScheduler::YieldThreadAndBalanceLoad(Thread* yielding_thread) {
// Note: caller should check if !thread.IsSchedulerOperationRedundant and use critical section,
// etc.
const u32 core_id = static_cast<u32>(yielding_thread->GetProcessorID());
const u32 priority = yielding_thread->GetPriority();
// Yield the thread
ASSERT_MSG(yielding_thread == scheduled_queue[core_id].front(priority),
"Thread yielding without being in front");
scheduled_queue[core_id].yield(priority);
std::array<Thread*, NUM_CPU_CORES> current_threads;
for (u32 i = 0; i < NUM_CPU_CORES; i++) {
current_threads[i] = scheduled_queue[i].empty() ? nullptr : scheduled_queue[i].front();
}
Thread* next_thread = scheduled_queue[core_id].front(priority);
Thread* winner = nullptr;
for (auto& thread : suggested_queue[core_id]) {
const s32 source_core = thread->GetProcessorID();
if (source_core >= 0) {
if (current_threads[source_core] != nullptr) {
if (thread == current_threads[source_core] ||
current_threads[source_core]->GetPriority() < min_regular_priority) {
continue;
}
}
}
if (next_thread->GetLastRunningTicks() >= thread->GetLastRunningTicks() ||
next_thread->GetPriority() < thread->GetPriority()) {
if (thread->GetPriority() <= priority) {
winner = thread;
break;
}
}
}
if (winner != nullptr) {
if (winner != yielding_thread) {
if (winner->IsRunning()) {
UnloadThread(winner->GetProcessorID());
}
TransferToCore(winner->GetPriority(), core_id, winner);
}
} else {
winner = next_thread;
}
return AskForReselectionOrMarkRedundant(yielding_thread, winner);
}
/*
* YieldThreadAndWaitForLoadBalancing takes a thread and moves it out of the scheduling queue
* and into the suggested queue. If no thread can be squeduled afterwards in that core,
* a suggested thread is obtained instead.
* This operation can be redundant and no scheduling is changed if marked as so.
*/
bool GlobalScheduler::YieldThreadAndWaitForLoadBalancing(Thread* yielding_thread) {
// Note: caller should check if !thread.IsSchedulerOperationRedundant and use critical section,
// etc.
Thread* winner = nullptr;
const u32 core_id = static_cast<u32>(yielding_thread->GetProcessorID());
// Remove the thread from its scheduled mlq, put it on the corresponding "suggested" one instead
TransferToCore(yielding_thread->GetPriority(), -1, yielding_thread);
// If the core is idle, perform load balancing, excluding the threads that have just used this
// function...
if (scheduled_queue[core_id].empty()) {
// Here, "current_threads" is calculated after the ""yield"", unlike yield -1
std::array<Thread*, NUM_CPU_CORES> current_threads;
for (u32 i = 0; i < NUM_CPU_CORES; i++) {
current_threads[i] = scheduled_queue[i].empty() ? nullptr : scheduled_queue[i].front();
}
for (auto& thread : suggested_queue[core_id]) {
const s32 source_core = thread->GetProcessorID();
if (source_core < 0 || thread == current_threads[source_core]) {
continue;
}
if (current_threads[source_core] == nullptr ||
current_threads[source_core]->GetPriority() >= min_regular_priority) {
winner = thread;
}
break;
}
if (winner != nullptr) {
if (winner != yielding_thread) {
if (winner->IsRunning()) {
UnloadThread(winner->GetProcessorID());
}
TransferToCore(winner->GetPriority(), core_id, winner);
}
} else {
winner = yielding_thread;
}
}
return AskForReselectionOrMarkRedundant(yielding_thread, winner);
}
void GlobalScheduler::PreemptThreads() {
for (std::size_t core_id = 0; core_id < NUM_CPU_CORES; core_id++) {
const u32 priority = preemption_priorities[core_id];
if (scheduled_queue[core_id].size(priority) > 0) {
scheduled_queue[core_id].front(priority)->IncrementYieldCount();
scheduled_queue[core_id].yield(priority);
if (scheduled_queue[core_id].size(priority) > 1) {
scheduled_queue[core_id].front(priority)->IncrementYieldCount();
}
}
Thread* current_thread =
scheduled_queue[core_id].empty() ? nullptr : scheduled_queue[core_id].front();
Thread* winner = nullptr;
for (auto& thread : suggested_queue[core_id]) {
const s32 source_core = thread->GetProcessorID();
if (thread->GetPriority() != priority) {
continue;
}
if (source_core >= 0) {
Thread* next_thread = scheduled_queue[source_core].empty()
? nullptr
: scheduled_queue[source_core].front();
if (next_thread != nullptr && next_thread->GetPriority() < 2) {
break;
}
if (next_thread == thread) {
continue;
}
}
if (current_thread != nullptr &&
current_thread->GetLastRunningTicks() >= thread->GetLastRunningTicks()) {
winner = thread;
break;
}
}
if (winner != nullptr) {
if (winner->IsRunning()) {
UnloadThread(winner->GetProcessorID());
}
TransferToCore(winner->GetPriority(), core_id, winner);
current_thread = winner->GetPriority() <= current_thread->GetPriority() ? winner : current_thread;
}
if (current_thread != nullptr && current_thread->GetPriority() > priority) {
for (auto& thread : suggested_queue[core_id]) {
const s32 source_core = thread->GetProcessorID();
if (thread->GetPriority() > priority) {
continue;
}
if (source_core >= 0) {
Thread* next_thread = scheduled_queue[source_core].empty()
? nullptr
: scheduled_queue[source_core].front();
if (next_thread != nullptr && next_thread->GetPriority() < 2) {
break;
}
if (next_thread == thread) {
continue;
}
}
if (current_thread != nullptr &&
current_thread->GetLastRunningTicks() >= thread->GetLastRunningTicks()) {
winner = thread;
break;
}
}
if (winner != nullptr) {
if (winner->IsRunning()) {
UnloadThread(winner->GetProcessorID());
}
TransferToCore(winner->GetPriority(), core_id, winner);
current_thread = winner;
}
}
reselection_pending.store(true, std::memory_order_release);
}
}
void GlobalScheduler::Schedule(u32 priority, u32 core, Thread* thread) {
ASSERT_MSG(thread->GetProcessorID() == core, "Thread must be assigned to this core.");
scheduled_queue[core].add(thread, priority);
}
void GlobalScheduler::SchedulePrepend(u32 priority, u32 core, Thread* thread) {
ASSERT_MSG(thread->GetProcessorID() == core, "Thread must be assigned to this core.");
scheduled_queue[core].add(thread, priority, false);
}
bool GlobalScheduler::AskForReselectionOrMarkRedundant(Thread* current_thread, Thread* winner) {
if (current_thread == winner) {
current_thread->IncrementYieldCount();
return true;
} else {
reselection_pending.store(true, std::memory_order_release);
return false;
}
}
GlobalScheduler::~GlobalScheduler() = default;
Scheduler::Scheduler(Core::System& system, Core::ARM_Interface& cpu_core, u32 core_id)
: system(system), cpu_core(cpu_core), core_id(core_id) {}
Scheduler::~Scheduler() = default;
bool Scheduler::HaveReadyThreads() const {
return system.GlobalScheduler().HaveReadyThreads(core_id);
}
Thread* Scheduler::GetCurrentThread() const {
return current_thread.get();
}
Thread* Scheduler::GetSelectedThread() const {
return selected_thread.get();
}
void Scheduler::SelectThreads() {
system.GlobalScheduler().SelectThread(core_id);
}
u64 Scheduler::GetLastContextSwitchTicks() const {
return last_context_switch_time;
}
void Scheduler::TryDoContextSwitch() {
if (context_switch_pending) {
SwitchContext();
}
}
void Scheduler::UnloadThread() {
Thread* const previous_thread = GetCurrentThread();
Process* const previous_process = system.Kernel().CurrentProcess();
UpdateLastContextSwitchTime(previous_thread, previous_process);
// Save context for previous thread
if (previous_thread) {
cpu_core.SaveContext(previous_thread->GetContext());
// Save the TPIDR_EL0 system register in case it was modified.
previous_thread->SetTPIDR_EL0(cpu_core.GetTPIDR_EL0());
if (previous_thread->GetStatus() == ThreadStatus::Running) {
// This is only the case when a reschedule is triggered without the current thread
// yielding execution (i.e. an event triggered, system core time-sliced, etc)
previous_thread->SetStatus(ThreadStatus::Ready);
}
previous_thread->SetIsRunning(false);
}
current_thread = nullptr;
}
void Scheduler::SwitchContext() {
Thread* const previous_thread = GetCurrentThread();
Thread* const new_thread = GetSelectedThread();
context_switch_pending = false;
if (new_thread == previous_thread) {
return;
}
Process* const previous_process = system.Kernel().CurrentProcess();
UpdateLastContextSwitchTime(previous_thread, previous_process);
// Save context for previous thread
if (previous_thread) {
cpu_core.SaveContext(previous_thread->GetContext());
// Save the TPIDR_EL0 system register in case it was modified.
previous_thread->SetTPIDR_EL0(cpu_core.GetTPIDR_EL0());
if (previous_thread->GetStatus() == ThreadStatus::Running) {
// This is only the case when a reschedule is triggered without the current thread
// yielding execution (i.e. an event triggered, system core time-sliced, etc)
previous_thread->SetStatus(ThreadStatus::Ready);
}
previous_thread->SetIsRunning(false);
}
// Load context of new thread
if (new_thread) {
ASSERT_MSG(new_thread->GetProcessorID() == this->core_id,
"Thread must be assigned to this core.");
ASSERT_MSG(new_thread->GetStatus() == ThreadStatus::Ready,
"Thread must be ready to become running.");
// Cancel any outstanding wakeup events for this thread
new_thread->CancelWakeupTimer();
current_thread = new_thread;
new_thread->SetStatus(ThreadStatus::Running);
new_thread->SetIsRunning(true);
auto* const thread_owner_process = current_thread->GetOwnerProcess();
if (previous_process != thread_owner_process) {
system.Kernel().MakeCurrentProcess(thread_owner_process);
}
cpu_core.LoadContext(new_thread->GetContext());
cpu_core.SetTlsAddress(new_thread->GetTLSAddress());
cpu_core.SetTPIDR_EL0(new_thread->GetTPIDR_EL0());
cpu_core.ClearExclusiveState();
} else {
current_thread = nullptr;
// Note: We do not reset the current process and current page table when idling because
// technically we haven't changed processes, our threads are just paused.
}
}
void Scheduler::UpdateLastContextSwitchTime(Thread* thread, Process* process) {
const u64 prev_switch_ticks = last_context_switch_time;
const u64 most_recent_switch_ticks = system.CoreTiming().GetTicks();
const u64 update_ticks = most_recent_switch_ticks - prev_switch_ticks;
if (thread != nullptr) {
thread->UpdateCPUTimeTicks(update_ticks);
}
if (process != nullptr) {
process->UpdateCPUTimeTicks(update_ticks);
}
last_context_switch_time = most_recent_switch_ticks;
}
} // namespace Kernel
