From 096c168dd7afe82a174e4df1bf548ba495672624 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Henrik=20Rydg=C3=A5rd?= <hrydgard@gmail.com>
Date: Mon, 7 Aug 2023 21:38:03 +0200
Subject: [PATCH] Add yield() function to tell the CPU that we're busy-waiting
 (rare) (#17862)

* Add yield() function to tell the CPU that we're busy-waiting (rare)

Use it only for the busy-wait in lag sync, which only happens in
Windows.

* Buildfix attempt
---
 Common/TimeUtil.cpp     | 22 +++++++++++++++++++++-
 Common/TimeUtil.h       |  3 +++
 Core/HLE/sceDisplay.cpp |  2 ++
 UI/EmuScreen.cpp        |  2 +-
 4 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/Common/TimeUtil.cpp b/Common/TimeUtil.cpp
index b149d1634572..099f026e3ce7 100644
--- a/Common/TimeUtil.cpp
+++ b/Common/TimeUtil.cpp
@@ -17,6 +17,12 @@
 #include <sys/time.h>
 #include <unistd.h>
 #endif
+
+// for _mm_pause
+#if PPSSPP_ARCH(X86) || PPSSPP_ARCH(AMD64)
+#include <immintrin.h>
+#endif
+
 #include <ctime>
 
 // TODO: https://github.com/floooh/sokol/blob/9a6237fcdf213e6da48e4f9201f144bcb2dcb46f/sokol_time.h#L229-L248
@@ -24,7 +30,7 @@
 static const double micros = 1000000.0;
 static const double nanos = 1000000000.0;
 
-#ifdef _WIN32
+#if PPSSPP_PLATFORM(WINDOWS)
 
 static LARGE_INTEGER frequency;
 static double frequencyMult;
@@ -58,6 +64,10 @@ double from_time_raw_relative(uint64_t raw_time) {
 	return from_time_raw(raw_time);
 }
 
+void yield() {
+	YieldProcessor();
+}
+
 #elif PPSSPP_PLATFORM(ANDROID) || PPSSPP_PLATFORM(LINUX) || PPSSPP_PLATFORM(MAC) || PPSSPP_PLATFORM(IOS)
 
 // The only intended use is to match the timings in VK_GOOGLE_display_timing
@@ -85,6 +95,14 @@ double from_time_raw_relative(uint64_t raw_time) {
 	return (double)raw_time * (1.0 / nanos);
 }
 
+void yield() {
+#if PPSSPP_ARCH(X86) || PPSSPP_ARCH(AMD64)
+	_mm_pause();
+#elif PPSSPP_ARCH(ARM64)
+	__builtin_arm_isb(15);
+#endif
+}
+
 #else
 
 double time_now_d() {
@@ -110,6 +128,8 @@ double from_time_raw_relative(uint64_t raw_time) {
 	return from_time_raw(raw_time);
 }
 
+void yield() {}
+
 #endif
 
 void sleep_ms(int ms) {
diff --git a/Common/TimeUtil.h b/Common/TimeUtil.h
index 0ba1d52adf2c..a0701ae097e7 100644
--- a/Common/TimeUtil.h
+++ b/Common/TimeUtil.h
@@ -16,6 +16,9 @@ double from_time_raw_relative(uint64_t raw_time);
 // Sleep. Does not necessarily have millisecond granularity, especially on Windows.
 void sleep_ms(int ms);
 
+// Yield. Signals that this thread is busy-waiting but wants to allow other hyperthreads to run.
+void yield();
+
 void GetTimeFormatted(char formattedTime[13]);
 
 // Rust-style Instant for clear and easy timing.
diff --git a/Core/HLE/sceDisplay.cpp b/Core/HLE/sceDisplay.cpp
index be8551c7fd17..5d907d475c0a 100644
--- a/Core/HLE/sceDisplay.cpp
+++ b/Core/HLE/sceDisplay.cpp
@@ -718,6 +718,8 @@ void hleLagSync(u64 userdata, int cyclesLate) {
 #ifndef _WIN32
 		const double left = goal - now;
 		usleep((long)(left * 1000000.0));
+#else
+		yield();
 #endif
 		now = time_now_d();
 	}
diff --git a/UI/EmuScreen.cpp b/UI/EmuScreen.cpp
index 85cf652041c2..66bb14a849d7 100644
--- a/UI/EmuScreen.cpp
+++ b/UI/EmuScreen.cpp
@@ -898,7 +898,7 @@ static UI::AnchorLayoutParams *AnchorInCorner(const Bounds &bounds, int corner,
 	switch ((ScreenEdgePosition)g_Config.iChatButtonPosition) {
 	case ScreenEdgePosition::BOTTOM_LEFT:   return new AnchorLayoutParams(WRAP_CONTENT, WRAP_CONTENT, xOffset, NONE, NONE, yOffset, true);
 	case ScreenEdgePosition::BOTTOM_CENTER: return new AnchorLayoutParams(WRAP_CONTENT, WRAP_CONTENT, bounds.centerX(), NONE, NONE, yOffset, true);
-	case ScreenEdgePosition::BOTTOM_RIGHT:   return new AnchorLayoutParams(WRAP_CONTENT, WRAP_CONTENT, NONE, NONE, xOffset, yOffset, true);
+	case ScreenEdgePosition::BOTTOM_RIGHT:  return new AnchorLayoutParams(WRAP_CONTENT, WRAP_CONTENT, NONE, NONE, xOffset, yOffset, true);
 	case ScreenEdgePosition::TOP_LEFT:      return new AnchorLayoutParams(WRAP_CONTENT, WRAP_CONTENT, xOffset, yOffset, NONE, NONE, true);
 	case ScreenEdgePosition::TOP_CENTER:    return new AnchorLayoutParams(WRAP_CONTENT, WRAP_CONTENT, bounds.centerX(), yOffset, NONE, NONE, true);
 	case ScreenEdgePosition::TOP_RIGHT:     return new AnchorLayoutParams(WRAP_CONTENT, WRAP_CONTENT, NONE, yOffset, xOffset, NONE, true);