Utilities: Add functions for spin waiting

common/CMakeLists.txt

@@ -20,6 +20,7 @@ target_sources(common PRIVATE
 	FastJmp.cpp
 	IniInterface.cpp
 	Mutex.cpp
+	Misc.cpp
 	PathUtils.cpp
 	PrecompiledHeader.cpp
 	Perf.cpp

common/General.h

@@ -217,6 +217,11 @@ extern void InitCPUTicks();
 extern u64 GetTickFrequency();
 extern u64 GetCPUTicks();
 extern u64 GetPhysicalMemory();
+/// Spin for a short period of time (call while spinning waiting for a lock)
+/// Returns the approximate number of ns that passed
+extern u32 ShortSpin();
+/// Number of ns to spin for before sleeping a thread
+extern const u32 SPIN_TIME_NS;
 
 extern wxString GetOSVersionString();
 

common/Misc.cpp

@@ -0,0 +1,73 @@
+/*  PCSX2 - PS2 Emulator for PCs
+ *  Copyright (C) 2021 PCSX2 Dev Team
+ *
+ *  PCSX2 is free software: you can redistribute it and/or modify it under the terms
+ *  of the GNU Lesser General Public License as published by the Free Software Found-
+ *  ation, either version 3 of the License, or (at your option) any later version.
+ *
+ *  PCSX2 is distributed in the hope that 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 PCSX2.
+ *  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "General.h"
+
+static u32 PAUSE_TIME = 0;
+
+static void MultiPause()
+{
+	_mm_pause();
+	_mm_pause();
+	_mm_pause();
+	_mm_pause();
+	_mm_pause();
+	_mm_pause();
+	_mm_pause();
+	_mm_pause();
+}
+
+__noinline static void UpdatePauseTime()
+{
+	u64 start = GetCPUTicks();
+	for (int i = 0; i < 64; i++)
+	{
+		MultiPause();
+	}
+	u64 time = GetCPUTicks() - start;
+	u64 nanos = (time * 1000000000) / GetTickFrequency();
+	PAUSE_TIME = (nanos / 64) + 1;
+}
+
+u32 ShortSpin()
+{
+	u32 inc = PAUSE_TIME;
+	if (unlikely(inc == 0))
+	{
+		UpdatePauseTime();
+		inc = PAUSE_TIME;
+	}
+
+	u32 time = 0;
+	// Sleep for approximately 500ns
+	for (; time < 500; time += inc)
+		MultiPause();
+
+	return time;
+}
+
+static u32 GetSpinTime()
+{
+	if (char* req = getenv("WAIT_SPIN_MICROSECONDS"))
+	{
+		return 1000 * atoi(req);
+	}
+	else
+	{
+		return 50 * 1000; // 50µs
+	}
+}
+
+const u32 SPIN_TIME_NS = GetSpinTime();

common/common.vcxproj

@@ -67,6 +67,7 @@
     <ClCompile Include="Windows\WinHostSys.cpp" />
     <ClCompile Include="Windows\WinMisc.cpp" />
     <ClCompile Include="Windows\WinThreads.cpp" />
+    <ClCompile Include="Misc.cpp" />
     <ClCompile Include="Mutex.cpp" />
     <ClCompile Include="RwMutex.cpp" />
     <ClCompile Include="Semaphore.cpp" />

common/common.vcxproj.filters

@@ -55,6 +55,9 @@
     <ClCompile Include="emitter\movs.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="Misc.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="Mutex.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>