kernel thread: Implement priority boost starved threads hack

src/common/settings.h

@@ -528,6 +528,7 @@ struct Values {
     SwitchableSetting<bool> force_hw_vertex_shaders{false, "force_hw_vertex_shaders"};
     SwitchableSetting<bool> disable_surface_texture_copy{false, "disable_surface_texture_copy"};
     SwitchableSetting<bool> disable_flush_cpu_write{false, "disable_flush_cpu_write"};
+    SwitchableSetting<bool> priority_boost_starved_threads{true, "priority_boost_starved_threads"};
 
     // Audio
     bool audio_muted;

src/core/hle/kernel/thread.cpp

@@ -156,6 +156,9 @@ void ThreadManager::SwitchContext(Thread* new_thread) {
             kernel.SetCurrentProcessForCPU(current_thread->owner_process.lock(), cpu->GetID());
         }
 
+        // Restores thread to its nominal priority if it has been temporarily changed
+        new_thread->current_priority = new_thread->nominal_priority;
+
         cpu->LoadContext(new_thread->context);
         cpu->SetCP15Register(CP15_THREAD_URO, new_thread->GetTLSAddress());
     } else {
@@ -469,7 +472,26 @@ bool ThreadManager::HaveReadyThreads() {
     return ready_queue.get_first() != nullptr;
 }
 
+void ThreadManager::PriorityBoostStarvedThreads() {
+    const u64 current_ticks = kernel.timing.GetTicks();
+
+    for (auto& thread : thread_list) {
+        const u64 boost_ticks = 1400000;
+
+        u64 delta = current_ticks - thread->last_running_ticks;
+
+        if (thread->status == ThreadStatus::Ready && delta > boost_ticks) {
+            const s32 priority = std::max(ready_queue.get_first()->current_priority, 40u);
+            thread->BoostPriority(priority);
+        }
+    }
+}
+
 void ThreadManager::Reschedule() {
+    if (Settings::values.priority_boost_starved_threads) {
+        PriorityBoostStarvedThreads();
+    }
+
     Thread* cur = GetCurrentThread();
     Thread* next = PopNextReadyThread();
 

src/core/hle/kernel/thread.h

@@ -142,6 +142,9 @@ class ThreadManager {
      */
     void ThreadWakeupCallback(u64 thread_id, s64 cycles_late);
 
+    /// Boost low priority starved threads
+    void PriorityBoostStarvedThreads();
+
     Kernel::KernelSystem& kernel;
     Core::ARM_Interface* cpu;