Atmosphere/libraries/libmesosphere/source/kern_k_scheduler.cpp

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/*
* Copyright (c) 2018-2020 Atmosphère-NX
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <mesosphere.hpp>
namespace ams::kern {
#pragma GCC push_options
#pragma GCC optimize ("-O3")
bool KScheduler::s_scheduler_update_needed;
KScheduler::LockType KScheduler::s_scheduler_lock;
KSchedulerPriorityQueue KScheduler::s_priority_queue;
namespace {
class KSchedulerInterruptTask : public KInterruptTask {
public:
constexpr KSchedulerInterruptTask() : KInterruptTask() { /* ... */ }
virtual KInterruptTask *OnInterrupt(s32 interrupt_id) override {
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MESOSPHERE_UNUSED(interrupt_id);
return GetDummyInterruptTask();
}
virtual void DoTask() override {
MESOSPHERE_PANIC("KSchedulerInterruptTask::DoTask was called!");
}
};
ALWAYS_INLINE void IncrementScheduledCount(KThread *thread) {
if (KProcess *parent = thread->GetOwnerProcess(); parent != nullptr) {
parent->IncrementScheduledCount();
}
}
KSchedulerInterruptTask g_scheduler_interrupt_task;
ALWAYS_INLINE auto *GetSchedulerInterruptTask() {
return std::addressof(g_scheduler_interrupt_task);
}
}
void KScheduler::Initialize(KThread *idle_thread) {
/* Set core ID and idle thread. */
m_core_id = GetCurrentCoreId();
m_idle_thread = idle_thread;
m_state.idle_thread_stack = m_idle_thread->GetStackTop();
/* Insert the main thread into the priority queue. */
{
KScopedSchedulerLock lk;
GetPriorityQueue().PushBack(GetCurrentThreadPointer());
SetSchedulerUpdateNeeded();
}
/* Bind interrupt handler. */
Kernel::GetInterruptManager().BindHandler(GetSchedulerInterruptTask(), KInterruptName_Scheduler, m_core_id, KInterruptController::PriorityLevel_Scheduler, false, false);
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/* Set the current thread. */
m_current_thread = GetCurrentThreadPointer();
}
void KScheduler::Activate() {
MESOSPHERE_ASSERT(GetCurrentThread().GetDisableDispatchCount() == 1);
m_state.should_count_idle = KTargetSystem::IsDebugMode();
m_is_active = true;
RescheduleCurrentCore();
}
void KScheduler::RescheduleOtherCores(u64 cores_needing_scheduling) {
if (const u64 core_mask = cores_needing_scheduling & ~(1ul << m_core_id); core_mask != 0) {
cpu::DataSynchronizationBarrier();
Kernel::GetInterruptManager().SendInterProcessorInterrupt(KInterruptName_Scheduler, core_mask);
}
}
u64 KScheduler::UpdateHighestPriorityThread(KThread *highest_thread) {
if (KThread *prev_highest_thread = m_state.highest_priority_thread; AMS_LIKELY(prev_highest_thread != highest_thread)) {
if (AMS_LIKELY(prev_highest_thread != nullptr)) {
IncrementScheduledCount(prev_highest_thread);
prev_highest_thread->SetLastScheduledTick(KHardwareTimer::GetTick());
}
if (m_state.should_count_idle) {
if (AMS_LIKELY(highest_thread != nullptr)) {
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if (KProcess *process = highest_thread->GetOwnerProcess(); process != nullptr) {
process->SetRunningThread(m_core_id, highest_thread, m_state.idle_count);
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}
} else {
m_state.idle_count++;
}
}
MESOSPHERE_KTRACE_SCHEDULE_UPDATE(m_core_id, (prev_highest_thread != nullptr ? prev_highest_thread : m_idle_thread), (highest_thread != nullptr ? highest_thread : m_idle_thread));
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m_state.highest_priority_thread = highest_thread;
m_state.needs_scheduling = true;
return (1ul << m_core_id);
} else {
return 0;
}
}
u64 KScheduler::UpdateHighestPriorityThreadsImpl() {
MESOSPHERE_ASSERT(IsSchedulerLockedByCurrentThread());
/* Clear that we need to update. */
ClearSchedulerUpdateNeeded();
u64 cores_needing_scheduling = 0, idle_cores = 0;
KThread *top_threads[cpu::NumCores];
auto &priority_queue = GetPriorityQueue();
/* We want to go over all cores, finding the highest priority thread and determining if scheduling is needed for that core. */
for (size_t core_id = 0; core_id < cpu::NumCores; core_id++) {
KThread *top_thread = priority_queue.GetScheduledFront(core_id);
if (top_thread != nullptr) {
/* If the thread has no waiters, we need to check if the process has a thread pinned. */
if (top_thread->GetNumKernelWaiters() == 0) {
if (KProcess *parent = top_thread->GetOwnerProcess(); parent != nullptr) {
if (KThread *pinned = parent->GetPinnedThread(core_id); pinned != nullptr && pinned != top_thread) {
/* We prefer our parent's pinned thread if possible. However, we also don't want to schedule un-runnable threads. */
if (pinned->GetRawState() == KThread::ThreadState_Runnable) {
top_thread = pinned;
} else {
top_thread = nullptr;
}
}
}
}
} else {
idle_cores |= (1ul << core_id);
}
top_threads[core_id] = top_thread;
cores_needing_scheduling |= Kernel::GetScheduler(core_id).UpdateHighestPriorityThread(top_threads[core_id]);
}
/* Idle cores are bad. We're going to try to migrate threads to each idle core in turn. */
while (idle_cores != 0) {
s32 core_id = __builtin_ctzll(idle_cores);
if (KThread *suggested = priority_queue.GetSuggestedFront(core_id); suggested != nullptr) {
s32 migration_candidates[cpu::NumCores];
size_t num_candidates = 0;
/* While we have a suggested thread, try to migrate it! */
while (suggested != nullptr) {
/* Check if the suggested thread is the top thread on its core. */
const s32 suggested_core = suggested->GetActiveCore();
if (KThread *top_thread = (suggested_core >= 0) ? top_threads[suggested_core] : nullptr; top_thread != suggested) {
/* Make sure we're not dealing with threads too high priority for migration. */
if (top_thread != nullptr && top_thread->GetPriority() < HighestCoreMigrationAllowedPriority) {
break;
}
/* The suggested thread isn't bound to its core, so we can migrate it! */
suggested->SetActiveCore(core_id);
priority_queue.ChangeCore(suggested_core, suggested);
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MESOSPHERE_KTRACE_CORE_MIGRATION(suggested->GetId(), suggested_core, core_id, 1);
top_threads[core_id] = suggested;
cores_needing_scheduling |= Kernel::GetScheduler(core_id).UpdateHighestPriorityThread(top_threads[core_id]);
break;
}
/* Note this core as a candidate for migration. */
MESOSPHERE_ASSERT(num_candidates < cpu::NumCores);
migration_candidates[num_candidates++] = suggested_core;
suggested = priority_queue.GetSuggestedNext(core_id, suggested);
}
/* If suggested is nullptr, we failed to migrate a specific thread. So let's try all our candidate cores' top threads. */
if (suggested == nullptr) {
for (size_t i = 0; i < num_candidates; i++) {
/* Check if there's some other thread that can run on the candidate core. */
const s32 candidate_core = migration_candidates[i];
suggested = top_threads[candidate_core];
if (KThread *next_on_candidate_core = priority_queue.GetScheduledNext(candidate_core, suggested); next_on_candidate_core != nullptr) {
/* The candidate core can run some other thread! We'll migrate its current top thread to us. */
top_threads[candidate_core] = next_on_candidate_core;
cores_needing_scheduling |= Kernel::GetScheduler(candidate_core).UpdateHighestPriorityThread(top_threads[candidate_core]);
/* Perform the migration. */
suggested->SetActiveCore(core_id);
priority_queue.ChangeCore(candidate_core, suggested);
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MESOSPHERE_KTRACE_CORE_MIGRATION(suggested->GetId(), candidate_core, core_id, 2);
top_threads[core_id] = suggested;
cores_needing_scheduling |= Kernel::GetScheduler(core_id).UpdateHighestPriorityThread(top_threads[core_id]);
break;
}
}
}
}
idle_cores &= ~(1ul << core_id);
}
return cores_needing_scheduling;
}
void KScheduler::InterruptTaskThreadToRunnable() {
MESOSPHERE_ASSERT(GetCurrentThread().GetDisableDispatchCount() == 1);
KThread *task_thread = Kernel::GetInterruptTaskManager().GetThread();
{
KScopedSchedulerLock sl;
task_thread->SetState(KThread::ThreadState_Runnable);
}
}
void KScheduler::SwitchThread(KThread *next_thread) {
KProcess *cur_process = GetCurrentProcessPointer();
KThread *cur_thread = GetCurrentThreadPointer();
/* We never want to schedule a null thread, so use the idle thread if we don't have a next. */
if (next_thread == nullptr) {
next_thread = m_idle_thread;
}
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if (next_thread->GetCurrentCore() != m_core_id) {
next_thread->SetCurrentCore(m_core_id);
}
/* If we're not actually switching thread, there's nothing to do. */
if (next_thread == cur_thread) {
return;
}
/* Next thread is now known not to be nullptr, and must not be dispatchable. */
MESOSPHERE_ASSERT(next_thread->GetDisableDispatchCount() == 1);
/* Update the CPU time tracking variables. */
const s64 prev_tick = m_last_context_switch_time;
const s64 cur_tick = KHardwareTimer::GetTick();
const s64 tick_diff = cur_tick - prev_tick;
cur_thread->AddCpuTime(m_core_id, tick_diff);
if (cur_process != nullptr) {
cur_process->AddCpuTime(tick_diff);
}
m_last_context_switch_time = cur_tick;
/* Update our previous thread. */
if (cur_process != nullptr) {
/* NOTE: Combining this into AMS_LIKELY(!... && ...) triggers an internal compiler error: Segmentation fault in GCC 9.2.0. */
if (AMS_LIKELY(!cur_thread->IsTerminationRequested()) && AMS_LIKELY(cur_thread->GetActiveCore() == m_core_id)) {
m_prev_thread = cur_thread;
} else {
m_prev_thread = nullptr;
}
} else if (cur_thread == m_idle_thread) {
m_prev_thread = nullptr;
}
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MESOSPHERE_KTRACE_THREAD_SWITCH(next_thread);
/* Switch the current process, if we're switching processes. */
if (KProcess *next_process = next_thread->GetOwnerProcess(); next_process != cur_process) {
KProcess::Switch(cur_process, next_process);
}
/* Set the new thread. */
SetCurrentThread(next_thread);
m_current_thread = next_thread;
/* Set the new Thread Local region. */
cpu::SwitchThreadLocalRegion(GetInteger(next_thread->GetThreadLocalRegionAddress()));
}
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void KScheduler::ClearPreviousThread(KThread *thread) {
MESOSPHERE_ASSERT(IsSchedulerLockedByCurrentThread());
for (size_t i = 0; i < cpu::NumCores; ++i) {
/* Get an atomic reference to the core scheduler's previous thread. */
std::atomic_ref<KThread *> prev_thread(Kernel::GetScheduler(static_cast<s32>(i)).m_prev_thread);
static_assert(std::atomic_ref<KThread *>::is_always_lock_free);
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/* Atomically clear the previous thread if it's our target. */
KThread *compare = thread;
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prev_thread.compare_exchange_strong(compare, nullptr);
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}
}
void KScheduler::OnThreadStateChanged(KThread *thread, KThread::ThreadState old_state) {
MESOSPHERE_ASSERT(IsSchedulerLockedByCurrentThread());
/* Check if the state has changed, because if it hasn't there's nothing to do. */
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const KThread::ThreadState cur_state = thread->GetRawState();
if (cur_state == old_state) {
return;
}
/* Update the priority queues. */
if (old_state == KThread::ThreadState_Runnable) {
/* If we were previously runnable, then we're not runnable now, and we should remove. */
GetPriorityQueue().Remove(thread);
IncrementScheduledCount(thread);
SetSchedulerUpdateNeeded();
} else if (cur_state == KThread::ThreadState_Runnable) {
/* If we're now runnable, then we weren't previously, and we should add. */
GetPriorityQueue().PushBack(thread);
IncrementScheduledCount(thread);
SetSchedulerUpdateNeeded();
}
}
void KScheduler::OnThreadPriorityChanged(KThread *thread, s32 old_priority) {
MESOSPHERE_ASSERT(IsSchedulerLockedByCurrentThread());
/* If the thread is runnable, we want to change its priority in the queue. */
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if (thread->GetRawState() == KThread::ThreadState_Runnable) {
GetPriorityQueue().ChangePriority(old_priority, thread == GetCurrentThreadPointer(), thread);
IncrementScheduledCount(thread);
SetSchedulerUpdateNeeded();
}
}
void KScheduler::OnThreadAffinityMaskChanged(KThread *thread, const KAffinityMask &old_affinity, s32 old_core) {
MESOSPHERE_ASSERT(IsSchedulerLockedByCurrentThread());
/* If the thread is runnable, we want to change its affinity in the queue. */
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if (thread->GetRawState() == KThread::ThreadState_Runnable) {
GetPriorityQueue().ChangeAffinityMask(old_core, old_affinity, thread);
IncrementScheduledCount(thread);
SetSchedulerUpdateNeeded();
}
}
void KScheduler::RotateScheduledQueue(s32 core_id, s32 priority) {
MESOSPHERE_ASSERT(IsSchedulerLockedByCurrentThread());
/* Get a reference to the priority queue. */
auto &priority_queue = GetPriorityQueue();
/* Rotate the front of the queue to the end. */
KThread *top_thread = priority_queue.GetScheduledFront(core_id, priority);
KThread *next_thread = nullptr;
if (top_thread != nullptr) {
next_thread = priority_queue.MoveToScheduledBack(top_thread);
if (next_thread != top_thread) {
IncrementScheduledCount(top_thread);
IncrementScheduledCount(next_thread);
}
}
/* While we have a suggested thread, try to migrate it! */
{
KThread *suggested = priority_queue.GetSuggestedFront(core_id, priority);
while (suggested != nullptr) {
/* Check if the suggested thread is the top thread on its core. */
const s32 suggested_core = suggested->GetActiveCore();
if (KThread *top_on_suggested_core = (suggested_core >= 0) ? priority_queue.GetScheduledFront(suggested_core) : nullptr; top_on_suggested_core != suggested) {
/* If the next thread is a new thread that has been waiting longer than our suggestion, we prefer it to our suggestion. */
if (top_thread != next_thread && next_thread != nullptr && next_thread->GetLastScheduledTick() < suggested->GetLastScheduledTick()) {
suggested = nullptr;
break;
}
/* If we're allowed to do a migration, do one. */
/* NOTE: Unlike migrations in UpdateHighestPriorityThread, this moves the suggestion to the front of the queue. */
if (top_on_suggested_core == nullptr || top_on_suggested_core->GetPriority() >= HighestCoreMigrationAllowedPriority) {
suggested->SetActiveCore(core_id);
priority_queue.ChangeCore(suggested_core, suggested, true);
IncrementScheduledCount(suggested);
break;
}
}
/* Get the next suggestion. */
suggested = priority_queue.GetSamePriorityNext(core_id, suggested);
}
}
/* Now that we might have migrated a thread with the same priority, check if we can do better. */
{
KThread *best_thread = priority_queue.GetScheduledFront(core_id);
if (best_thread == GetCurrentThreadPointer()) {
best_thread = priority_queue.GetScheduledNext(core_id, best_thread);
}
/* If the best thread we can choose has a priority the same or worse than ours, try to migrate a higher priority thread. */
if (best_thread != nullptr && best_thread->GetPriority() >= priority) {
KThread *suggested = priority_queue.GetSuggestedFront(core_id);
while (suggested != nullptr) {
/* If the suggestion's priority is the same as ours, don't bother. */
if (suggested->GetPriority() >= best_thread->GetPriority()) {
break;
}
/* Check if the suggested thread is the top thread on its core. */
const s32 suggested_core = suggested->GetActiveCore();
if (KThread *top_on_suggested_core = (suggested_core >= 0) ? priority_queue.GetScheduledFront(suggested_core) : nullptr; top_on_suggested_core != suggested) {
/* If we're allowed to do a migration, do one. */
/* NOTE: Unlike migrations in UpdateHighestPriorityThread, this moves the suggestion to the front of the queue. */
if (top_on_suggested_core == nullptr || top_on_suggested_core->GetPriority() >= HighestCoreMigrationAllowedPriority) {
suggested->SetActiveCore(core_id);
priority_queue.ChangeCore(suggested_core, suggested, true);
IncrementScheduledCount(suggested);
break;
}
}
/* Get the next suggestion. */
suggested = priority_queue.GetSuggestedNext(core_id, suggested);
}
}
}
/* After a rotation, we need a scheduler update. */
SetSchedulerUpdateNeeded();
}
void KScheduler::YieldWithoutCoreMigration() {
/* Validate preconditions. */
MESOSPHERE_ASSERT(CanSchedule());
MESOSPHERE_ASSERT(GetCurrentProcessPointer() != nullptr);
/* Get the current thread and process. */
KThread &cur_thread = GetCurrentThread();
KProcess &cur_process = GetCurrentProcess();
/* If the thread's yield count matches, there's nothing for us to do. */
if (cur_thread.GetYieldScheduleCount() == cur_process.GetScheduledCount()) {
return;
}
/* Get a reference to the priority queue. */
auto &priority_queue = GetPriorityQueue();
/* Perform the yield. */
{
KScopedSchedulerLock sl;
const auto cur_state = cur_thread.GetRawState();
if (cur_state == KThread::ThreadState_Runnable) {
/* Put the current thread at the back of the queue. */
KThread *next_thread = priority_queue.MoveToScheduledBack(std::addressof(cur_thread));
IncrementScheduledCount(std::addressof(cur_thread));
/* If the next thread is different, we have an update to perform. */
if (next_thread != std::addressof(cur_thread)) {
SetSchedulerUpdateNeeded();
} else {
/* Otherwise, set the thread's yield count so that we won't waste work until the process is scheduled again. */
cur_thread.SetYieldScheduleCount(cur_process.GetScheduledCount());
}
}
}
}
void KScheduler::YieldWithCoreMigration() {
/* Validate preconditions. */
MESOSPHERE_ASSERT(CanSchedule());
MESOSPHERE_ASSERT(GetCurrentProcessPointer() != nullptr);
/* Get the current thread and process. */
KThread &cur_thread = GetCurrentThread();
KProcess &cur_process = GetCurrentProcess();
/* If the thread's yield count matches, there's nothing for us to do. */
if (cur_thread.GetYieldScheduleCount() == cur_process.GetScheduledCount()) {
return;
}
/* Get a reference to the priority queue. */
auto &priority_queue = GetPriorityQueue();
/* Perform the yield. */
{
KScopedSchedulerLock sl;
const auto cur_state = cur_thread.GetRawState();
if (cur_state == KThread::ThreadState_Runnable) {
/* Get the current active core. */
const s32 core_id = cur_thread.GetActiveCore();
/* Put the current thread at the back of the queue. */
KThread *next_thread = priority_queue.MoveToScheduledBack(std::addressof(cur_thread));
IncrementScheduledCount(std::addressof(cur_thread));
/* While we have a suggested thread, try to migrate it! */
bool recheck = false;
KThread *suggested = priority_queue.GetSuggestedFront(core_id);
while (suggested != nullptr) {
/* Check if the suggested thread is the thread running on its core. */
const s32 suggested_core = suggested->GetActiveCore();
if (KThread *running_on_suggested_core = (suggested_core >= 0) ? Kernel::GetScheduler(suggested_core).m_state.highest_priority_thread : nullptr; running_on_suggested_core != suggested) {
/* If the current thread's priority is higher than our suggestion's we prefer the next thread to the suggestion. */
/* We also prefer the next thread when the current thread's priority is equal to the suggestions, but the next thread has been waiting longer. */
if ((suggested->GetPriority() > cur_thread.GetPriority()) ||
(suggested->GetPriority() == cur_thread.GetPriority() && next_thread != std::addressof(cur_thread) && next_thread->GetLastScheduledTick() < suggested->GetLastScheduledTick()))
{
suggested = nullptr;
break;
}
/* If we're allowed to do a migration, do one. */
/* NOTE: Unlike migrations in UpdateHighestPriorityThread, this moves the suggestion to the front of the queue. */
if (running_on_suggested_core == nullptr || running_on_suggested_core->GetPriority() >= HighestCoreMigrationAllowedPriority) {
suggested->SetActiveCore(core_id);
priority_queue.ChangeCore(suggested_core, suggested, true);
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MESOSPHERE_KTRACE_CORE_MIGRATION(suggested->GetId(), suggested_core, core_id, 3);
IncrementScheduledCount(suggested);
break;
} else {
/* We couldn't perform a migration, but we should check again on a future yield. */
recheck = true;
}
}
/* Get the next suggestion. */
suggested = priority_queue.GetSuggestedNext(core_id, suggested);
}
/* If we still have a suggestion or the next thread is different, we have an update to perform. */
if (suggested != nullptr || next_thread != std::addressof(cur_thread)) {
SetSchedulerUpdateNeeded();
} else if (!recheck) {
/* Otherwise if we don't need to re-check, set the thread's yield count so that we won't waste work until the process is scheduled again. */
cur_thread.SetYieldScheduleCount(cur_process.GetScheduledCount());
}
}
}
}
void KScheduler::YieldToAnyThread() {
/* Validate preconditions. */
MESOSPHERE_ASSERT(CanSchedule());
MESOSPHERE_ASSERT(GetCurrentProcessPointer() != nullptr);
/* Get the current thread and process. */
KThread &cur_thread = GetCurrentThread();
KProcess &cur_process = GetCurrentProcess();
/* If the thread's yield count matches, there's nothing for us to do. */
if (cur_thread.GetYieldScheduleCount() == cur_process.GetScheduledCount()) {
return;
}
/* Get a reference to the priority queue. */
auto &priority_queue = GetPriorityQueue();
/* Perform the yield. */
{
KScopedSchedulerLock sl;
const auto cur_state = cur_thread.GetRawState();
if (cur_state == KThread::ThreadState_Runnable) {
/* Get the current active core. */
const s32 core_id = cur_thread.GetActiveCore();
/* Migrate the current thread to core -1. */
cur_thread.SetActiveCore(-1);
priority_queue.ChangeCore(core_id, std::addressof(cur_thread));
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MESOSPHERE_KTRACE_CORE_MIGRATION(cur_thread.GetId(), core_id, -1, 4);
IncrementScheduledCount(std::addressof(cur_thread));
/* If there's nothing scheduled, we can try to perform a migration. */
if (priority_queue.GetScheduledFront(core_id) == nullptr) {
/* While we have a suggested thread, try to migrate it! */
KThread *suggested = priority_queue.GetSuggestedFront(core_id);
while (suggested != nullptr) {
/* Check if the suggested thread is the top thread on its core. */
const s32 suggested_core = suggested->GetActiveCore();
if (KThread *top_on_suggested_core = (suggested_core >= 0) ? priority_queue.GetScheduledFront(suggested_core) : nullptr; top_on_suggested_core != suggested) {
/* If we're allowed to do a migration, do one. */
if (top_on_suggested_core == nullptr || top_on_suggested_core->GetPriority() >= HighestCoreMigrationAllowedPriority) {
suggested->SetActiveCore(core_id);
priority_queue.ChangeCore(suggested_core, suggested);
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MESOSPHERE_KTRACE_CORE_MIGRATION(suggested->GetId(), suggested_core, core_id, 5);
IncrementScheduledCount(suggested);
}
/* Regardless of whether we migrated, we had a candidate, so we're done. */
break;
}
/* Get the next suggestion. */
suggested = priority_queue.GetSuggestedNext(core_id, suggested);
}
/* If the suggestion is different from the current thread, we need to perform an update. */
if (suggested != std::addressof(cur_thread)) {
SetSchedulerUpdateNeeded();
} else {
/* Otherwise, set the thread's yield count so that we won't waste work until the process is scheduled again. */
cur_thread.SetYieldScheduleCount(cur_process.GetScheduledCount());
}
} else {
/* Otherwise, we have an update to perform. */
SetSchedulerUpdateNeeded();
}
}
}
}
#pragma GCC pop_options
}