Fifo: only sleep once within every ms of emulated time

Source/Core/Core/HW/SystemTimers.cpp

@@ -199,6 +199,9 @@ static void PatchEngineCallback(u64 userdata, int cyclesLate)
 
 static void ThrottleCallback(u64 last_time, int cyclesLate)
 {
+	// Allow the GPU thread to sleep. Setting this flag here limits the wakeups to 1 kHz.
+	CommandProcessor::s_gpuMaySleep.Set();
+
 	u32 time = Common::Timer::GetTimeMs();
 
 	int diff = (u32)last_time - time;

Source/Core/VideoCommon/CommandProcessor.cpp

@@ -45,6 +45,8 @@ volatile bool interruptWaiting= false;
 volatile bool interruptTokenWaiting = false;
 volatile bool interruptFinishWaiting = false;
 
+Common::Flag s_gpuMaySleep;
+
 volatile u32 VITicks = CommandProcessor::m_cpClockOrigin;
 
 static bool IsOnThread()

Source/Core/VideoCommon/CommandProcessor.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include "Common/CommonTypes.h"
+#include "Common/Flag.h"
 #include "VideoCommon/VideoBackendBase.h"
 
 class PointerWrap;
@@ -21,6 +22,7 @@ extern volatile bool interruptSet;
 extern volatile bool interruptWaiting;
 extern volatile bool interruptTokenWaiting;
 extern volatile bool interruptFinishWaiting;
+extern Common::Flag s_gpuMaySleep;
 
 // internal hardware addresses
 enum

Source/Core/VideoCommon/Fifo.cpp

@@ -369,9 +369,13 @@ void RunGpuLoop()
 		{
 			if (s_gpu_is_running.IsSet())
 			{
-				// reset the atomic flag. But as the CPU thread might have pushed some new data, we have to rerun the GPU loop
-				s_gpu_is_pending.Set();
-				s_gpu_is_running.Clear();
+				if (CommandProcessor::s_gpuMaySleep.IsSet())
+				{
+					// Reset the atomic flag. But as the CPU thread might have pushed some new data, we have to rerun the GPU loop
+					s_gpu_is_pending.Set();
+					s_gpu_is_running.Clear();
+					CommandProcessor::s_gpuMaySleep.Clear();
+				}
 			}
 			else
 			{
@@ -403,6 +407,7 @@ void FlushGpu()
 
 	while (s_gpu_is_running.IsSet() || s_gpu_is_pending.IsSet())
 	{
+		CommandProcessor::s_gpuMaySleep.Set();
 		s_gpu_done_event.Wait();
 	}
 }