Threading: Reworked the way our scheduler works.

Threads will now be awakened when the objects they're waiting on are signaled, instead of repeating the WaitSynchronization call every now and then.

The scheduler is now called once after every SVC call, and once after a thread is awakened from sleep by its timeout callback.

This new implementation is based off reverse-engineering of the real kernel.

See https://gist.github.com/Subv/02f29bd9f1e5deb7aceea1e8f019c8f4 for a more detailed description of how the real kernel handles rescheduling.

1 files changed, 3 insertions, 94 deletions

diff --git a/src/core/hle/kernel/thread.cpp b/src/core/hle/kernel/thread.cpp
index 84d6d24c6..49ed9d899 100644
--- a/src/core/hle/kernel/thread.cpp
+++ b/src/core/hle/kernel/thread.cpp
@@ -120,8 +120,6 @@ void Thread::Stop() {
     u32 tls_slot =
         ((tls_address - Memory::TLS_AREA_VADDR) % Memory::PAGE_SIZE) / Memory::TLS_ENTRY_SIZE;
     Kernel::g_current_process->tls_slots[tls_page].reset(tls_slot);
-
-    HLE::Reschedule(__func__);
 }
 
 Thread* ArbitrateHighestPriorityThread(u32 address) {
@@ -181,50 +179,6 @@ static void PriorityBoostStarvedThreads() {
 }
 
 /**
- * Gets the registers for timeout parameter of the next WaitSynchronization call.
- * @param thread a pointer to the thread that is ready to call WaitSynchronization
- * @returns a tuple of two register pointers to low and high part of the timeout parameter
- */
-static std::tuple<u32*, u32*> GetWaitSynchTimeoutParameterRegister(Thread* thread) {
-    bool thumb_mode = (thread->context.cpsr & TBIT) != 0;
-    u16 thumb_inst = Memory::Read16(thread->context.pc & 0xFFFFFFFE);
-    u32 inst = Memory::Read32(thread->context.pc & 0xFFFFFFFC) & 0x0FFFFFFF;
-
-    if ((thumb_mode && thumb_inst == 0xDF24) || (!thumb_mode && inst == 0x0F000024)) {
-        // svc #0x24 (WaitSynchronization1)
-        return std::make_tuple(&thread->context.cpu_registers[2],
-                               &thread->context.cpu_registers[3]);
-    } else if ((thumb_mode && thumb_inst == 0xDF25) || (!thumb_mode && inst == 0x0F000025)) {
-        // svc #0x25 (WaitSynchronizationN)
-        return std::make_tuple(&thread->context.cpu_registers[0],
-                               &thread->context.cpu_registers[4]);
-    }
-
-    UNREACHABLE();
-}
-
-/**
- * Updates the WaitSynchronization timeout parameter according to the difference
- * between ticks of the last WaitSynchronization call and the incoming one.
- * @param timeout_low a pointer to the register for the low part of the timeout parameter
- * @param timeout_high a pointer to the register for the high part of the timeout parameter
- * @param last_tick tick of the last WaitSynchronization call
- */
-static void UpdateTimeoutParameter(u32* timeout_low, u32* timeout_high, u64 last_tick) {
-    s64 timeout = ((s64)*timeout_high << 32) | *timeout_low;
-
-    if (timeout != -1) {
-        timeout -= cyclesToUs(CoreTiming::GetTicks() - last_tick) * 1000; // in nanoseconds
-
-        if (timeout < 0)
-            timeout = 0;
-
-        *timeout_low = timeout & 0xFFFFFFFF;
-        *timeout_high = timeout >> 32;
-    }
-}
-
-/**
  * Switches the CPU's active thread context to that of the specified thread
  * @param new_thread The thread to switch to
  */
@@ -254,32 +208,6 @@ static void SwitchContext(Thread* new_thread) {
 
         current_thread = new_thread;
 
-        // If the thread was waited by a svcWaitSynch call, step back PC by one instruction to rerun
-        // the SVC when the thread wakes up. This is necessary to ensure that the thread can acquire
-        // the requested wait object(s) before continuing.
-        if (new_thread->waitsynch_waited) {
-            // CPSR flag indicates CPU mode
-            bool thumb_mode = (new_thread->context.cpsr & TBIT) != 0;
-
-            // SVC instruction is 2 bytes for THUMB, 4 bytes for ARM
-            new_thread->context.pc -= thumb_mode ? 2 : 4;
-
-            // Get the register for timeout parameter
-            u32 *timeout_low, *timeout_high;
-            std::tie(timeout_low, timeout_high) = GetWaitSynchTimeoutParameterRegister(new_thread);
-
-            // Update the timeout parameter
-            UpdateTimeoutParameter(timeout_low, timeout_high, new_thread->last_running_ticks);
-        }
-
-        // Clean up the thread's wait_objects, they'll be restored if needed during
-        // the svcWaitSynchronization call
-        for (size_t i = 0; i < new_thread->wait_objects.size(); ++i) {
-            SharedPtr<WaitObject> object = new_thread->wait_objects[i];
-            object->RemoveWaitingThread(new_thread);
-        }
-        new_thread->wait_objects.clear();
-
         ready_queue.remove(new_thread->current_priority, new_thread);
         new_thread->status = THREADSTATUS_RUNNING;
 
@@ -319,17 +247,13 @@ static Thread* PopNextReadyThread() {
 void WaitCurrentThread_Sleep() {
     Thread* thread = GetCurrentThread();
     thread->status = THREADSTATUS_WAIT_SLEEP;
-
-    HLE::Reschedule(__func__);
 }
 
 void WaitCurrentThread_WaitSynchronization(std::vector<SharedPtr<WaitObject>> wait_objects,
-                                           bool wait_set_output, bool wait_all) {
+                                           bool wait_set_output) {
     Thread* thread = GetCurrentThread();
     thread->wait_set_output = wait_set_output;
-    thread->wait_all = wait_all;
     thread->wait_objects = std::move(wait_objects);
-    thread->waitsynch_waited = true;
     thread->status = THREADSTATUS_WAIT_SYNCH;
 }
 
@@ -351,15 +275,11 @@ static void ThreadWakeupCallback(u64 thread_handle, int cycles_late) {
         return;
     }
 
-    thread->waitsynch_waited = false;
-
     if (thread->status == THREADSTATUS_WAIT_SYNCH || thread->status == THREADSTATUS_WAIT_ARB) {
+        thread->wait_set_output = false;
         thread->SetWaitSynchronizationResult(ResultCode(ErrorDescription::Timeout, ErrorModule::OS,
                                                         ErrorSummary::StatusChanged,
                                                         ErrorLevel::Info));
-
-        if (thread->wait_set_output)
-            thread->SetWaitSynchronizationOutput(-1);
     }
 
     thread->ResumeFromWait();
@@ -399,6 +319,7 @@ void Thread::ResumeFromWait() {
 
     ready_queue.push_back(current_priority, this);
     status = THREADSTATUS_READY;
+    HLE::Reschedule(__func__);
 }
 
 /**
@@ -494,13 +415,11 @@ ResultVal<SharedPtr<Thread>> Thread::Create(std::string name, VAddr entry_point,
     thread->last_running_ticks = CoreTiming::GetTicks();
     thread->processor_id = processor_id;
     thread->wait_set_output = false;
-    thread->wait_all = false;
     thread->wait_objects.clear();
     thread->wait_address = 0;
     thread->name = std::move(name);
     thread->callback_handle = wakeup_callback_handle_table.Create(thread).MoveFrom();
     thread->owner_process = g_current_process;
-    thread->waitsynch_waited = false;
 
     // Find the next available TLS index, and mark it as used
     auto& tls_slots = Kernel::g_current_process->tls_slots;
@@ -555,8 +474,6 @@ ResultVal<SharedPtr<Thread>> Thread::Create(std::string name, VAddr entry_point,
     ready_queue.push_back(thread->current_priority, thread.get());
     thread->status = THREADSTATUS_READY;
 
-    HLE::Reschedule(__func__);
-
     return MakeResult<SharedPtr<Thread>>(std::move(thread));
 }
 
@@ -619,14 +536,6 @@ void Reschedule() {
 
     HLE::DoneRescheduling();
 
-    // Don't bother switching to the same thread.
-    // But if the thread was waiting on objects, we still need to switch it
-    // to perform PC modification, change state to RUNNING, etc.
-    // This occurs in the case when an object the thread is waiting on immediately wakes up
-    // the current thread before Reschedule() is called.
-    if (next == cur && (next == nullptr || next->waitsynch_waited == false))
-        return;
-
     if (cur && next) {
         LOG_TRACE(Kernel, "context switch %u -> %u", cur->GetObjectId(), next->GetObjectId());
     } else if (cur) {