Disable the GPU mutex in single core mode. On some platforms it's expensive enough to show up in profiles even though it's useless.

GPU/GPUCommon.cpp

@@ -41,6 +41,7 @@ GPUCommon::GPUCommon() :
 	// The compiler was not rounding the struct size up to an 8 byte boundary, which
 	// you'd expect due to the int64 field, but the Linux ABI apparently does not require that.
 	static_assert(sizeof(DisplayList) == 456, "Bad DisplayList size");
+	listLock.set_enabled(g_Config.bSeparateCPUThread);
 
 	Reinitialize();
 	SetupColorConv();
@@ -136,7 +137,7 @@ void GPUCommon::PopDLQueue() {
 bool GPUCommon::BusyDrawing() {
 	u32 state = DrawSync(1);
 	if (state == PSP_GE_LIST_DRAWING || state == PSP_GE_LIST_STALLING) {
-		lock_guard guard(listLock);
+		easy_guard guard(listLock);
 		if (currentList && currentList->state != PSP_GE_DL_STATE_PAUSED) {
 			return true;
 		}

GPU/GPUCommon.h

@@ -216,12 +216,21 @@ protected:
 	// Allows early unlocking with a guard.  Do not double unlock.
 	class easy_guard {
 	public:
-		easy_guard(recursive_mutex &mtx) : mtx_(mtx), locked_(true) { mtx_.lock(); }
-		~easy_guard() { if (locked_) mtx_.unlock(); }
-		void unlock() { if (locked_) mtx_.unlock(); else Crash(); locked_ = false; }
+		easy_guard(optional_recursive_mutex &mtx) : mtx_(mtx), locked_(true) { mtx_.lock(); }
+		~easy_guard() {
+			if (locked_)
+				mtx_.unlock();
+		}
+		void unlock() {
+			if (locked_)
+				mtx_.unlock();
+			else
+				Crash();
+			locked_ = false;
+		}
 
 	private:
-		recursive_mutex &mtx_;
+		optional_recursive_mutex &mtx_;
 		bool locked_;
 	};
 
@@ -236,7 +245,7 @@ protected:
 	DisplayList dls[DisplayListMaxCount];
 	DisplayList *currentList;
 	DisplayListQueue dlQueue;
-	recursive_mutex listLock;
+	optional_recursive_mutex listLock;
 
 	bool interruptRunning;
 	GPURunState gpuState;

ext/native/base/mutex.h

@@ -139,6 +139,31 @@ private:
 	recursive_mutex &mtx_;
 };
 
+// This mutex can be disabled, which is useful for single core mode.
+class optional_recursive_mutex {
+public:
+	optional_recursive_mutex() : enabled_(true) {}
+	void set_enabled(bool enabled) {
+		enabled_ = enabled;
+	}
+	void lock() {
+		if (enabled_)
+			mutex_.lock();
+	}
+	void unlock() {
+		if (enabled_)
+			mutex_.unlock();
+	}
+	bool trylock() {
+		if (enabled_)
+			return mutex_.trylock();
+		else
+			return true;
+	}
+private:
+	recursive_mutex mutex_;
+	bool enabled_;
+};
 
 // Like a Windows event, or a modern condition variable.