[android, core] pin core threads to logical CPUs 0-3 (#3121)

this basically allows the threads to exist in these logical CPUs, undisturbed, and without trashing each other's cache
this could improve performance, very tricky thing to pull off correctly, but again, this is mostly an experiment
will mainly benefit: Linux, Android, FreeBSD, Windows (not ARM)
Additionally, this means no context trashing :)

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Co-authored-by: Caio Oliveira <caiooliveirafarias0@gmail.com>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3121
Reviewed-by: DraVee <dravee@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

3 files changed, 51 insertions, 31 deletions

diff --git a/src/common/thread.cpp b/src/common/thread.cpp
index 482848b244..eac0f60131 100644
--- a/src/common/thread.cpp
+++ b/src/common/thread.cpp
@@ -1,13 +1,15 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 // SPDX-FileCopyrightText: 2013 Dolphin Emulator Project
 // SPDX-FileCopyrightText: 2014 Citra Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <string>
+#include <thread>
 
 #include "common/error.h"
 #include "common/logging/log.h"
+#include "common/assert.h"
 #include "common/thread.h"
 #ifdef __APPLE__
 #include <mach/mach.h>
@@ -18,6 +20,8 @@
 #include "common/string_util.h"
 #else
 #if defined(__Bitrig__) || defined(__DragonFly__) || defined(__FreeBSD__) || defined(__OpenBSD__)
+#include <sys/cpuset.h>
+#include <sys/_cpuset.h>
 #include <pthread_np.h>
 #endif
 #include <pthread.h>
@@ -28,7 +32,7 @@
 #endif
 
 #ifdef __FreeBSD__
-#define cpu_set_t cpuset_t
+#   define cpu_set_t cpuset_t
 #endif
 
 namespace Common {
@@ -77,22 +81,14 @@ void SetCurrentThreadPriority(ThreadPriority new_priority) {
 #endif
 }
 
-#ifdef _MSC_VER
-
-// Sets the debugger-visible name of the current thread.
 void SetCurrentThreadName(const char* name) {
-    static auto pf = (decltype(&SetThreadDescription))(void*)GetProcAddress(GetModuleHandle(TEXT("KernelBase.dll")), "SetThreadDescription");
-    if (pf)
+#ifdef _MSC_VER
+    // Sets the debugger-visible name of the current thread.
+    if (auto pf = (decltype(&SetThreadDescription))(void*)GetProcAddress(GetModuleHandle(TEXT("KernelBase.dll")), "SetThreadDescription"); pf)
         pf(GetCurrentThread(), UTF8ToUTF16W(name).data()); // Windows 10+
-}
-
-#else // !MSVC_VER, so must be POSIX threads
-
-// MinGW with the POSIX threading model does not support pthread_setname_np
-void SetCurrentThreadName(const char* name) {
-    // See for reference
-    // https://gitlab.freedesktop.org/mesa/mesa/-/blame/main/src/util/u_thread.c?ref_type=heads#L75
-#ifdef __APPLE__
+    else
+        ; // No-op
+#elif  defined(__APPLE__)
     pthread_setname_np(name);
 #elif defined(__HAIKU__)
     rename_thread(find_thread(NULL), name);
@@ -112,13 +108,38 @@ void SetCurrentThreadName(const char* name) {
         pthread_setname_np(pthread_self(), buf);
     }
 #elif defined(_WIN32)
-    // mingw stub
+    // MinGW with the POSIX threading model does not support pthread_setname_np
+    // See for reference
+    // https://gitlab.freedesktop.org/mesa/mesa/-/blame/main/src/util/u_thread.c?ref_type=heads#L75
     (void)name;
 #else
     pthread_setname_np(pthread_self(), name);
 #endif
 }
 
+void PinCurrentThreadToPerformanceCore(size_t core_id) {
+    ASSERT(core_id < 4);
+    // If we set a flag for a CPU that doesn't exist, the thread may not be allowed to
+    // run in ANY processor!
+    auto const total_cores = std::thread::hardware_concurrency();
+    if (core_id < total_cores) {
+#if defined(__ANDROID__)
+        cpu_set_t set;
+        CPU_ZERO(&set);
+        CPU_SET(core_id, &set);
+        sched_setaffinity(pthread_self(), sizeof(set), &set);
+#elif defined(__linux__) || defined(__FreeBSD__)
+        cpu_set_t set;
+        CPU_ZERO(&set);
+        CPU_SET(core_id, &set);
+        pthread_setaffinity_np(pthread_self(), sizeof(set), &set);
+#elif defined(_WIN32)
+        DWORD set = 1UL << core_id;
+        SetThreadAffinityMask(GetCurrentThread(), set);
+#else
+        // No pin functionality implemented
 #endif
+    }
+}
 
 } // namespace Common
diff --git a/src/common/thread.h b/src/common/thread.h
index 5ab495baaa..ea6f5d6b3b 100644
--- a/src/common/thread.h
+++ b/src/common/thread.h
@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 // SPDX-FileCopyrightText: 2013 Dolphin Emulator Project
@@ -106,7 +106,7 @@ enum class ThreadPriority : u32 {
 };
 
 void SetCurrentThreadPriority(ThreadPriority new_priority);
-
 void SetCurrentThreadName(const char* name);
+void PinCurrentThreadToPerformanceCore(size_t core_id);
 
 } // namespace Common
diff --git a/src/core/cpu_manager.cpp b/src/core/cpu_manager.cpp
index 1a80fcfaa4..10fdcdf8a2 100644
--- a/src/core/cpu_manager.cpp
+++ b/src/core/cpu_manager.cpp
@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
@@ -7,6 +7,7 @@
 #include "common/fiber.h"
 #include "common/scope_exit.h"
 #include "common/thread.h"
+#include "common/settings.h"
 #include "core/core.h"
 #include "core/core_timing.h"
 #include "core/cpu_manager.h"
@@ -25,11 +26,8 @@ CpuManager::~CpuManager() = default;
 void CpuManager::Initialize() {
     num_cores = is_multicore ? Core::Hardware::NUM_CPU_CORES : 1;
     gpu_barrier = std::make_unique<Common::Barrier>(num_cores + 1);
-
-    for (std::size_t core = 0; core < num_cores; core++) {
-        core_data[core].host_thread =
-            std::jthread([this, core](std::stop_token token) { RunThread(token, core); });
-    }
+    for (std::size_t core = 0; core < num_cores; core++)
+        core_data[core].host_thread = std::jthread([this, core](std::stop_token token) { RunThread(token, core); });
 }
 
 void CpuManager::Shutdown() {
@@ -188,14 +186,15 @@ void CpuManager::ShutdownThread() {
 void CpuManager::RunThread(std::stop_token token, std::size_t core) {
     /// Initialization
     system.RegisterCoreThread(core);
-    std::string name;
-    if (is_multicore) {
-        name = "CPUCore_" + std::to_string(core);
-    } else {
-        name = "CPUThread";
-    }
+    std::string name = is_multicore ? ("CPUCore_" + std::to_string(core)) : std::string{"CPUThread"};
     Common::SetCurrentThreadName(name.c_str());
     Common::SetCurrentThreadPriority(Common::ThreadPriority::Critical);
+#ifdef __ANDROID__
+    // Aimed specifically for Snapdragon 8 Elite devices
+    // This kills performance on desktop, but boosts perf for UMA devices
+    // like the S8E. Mediatek and Mali likely won't suffer.
+    Common::PinCurrentThreadToPerformanceCore(core);
+#endif
     auto& data = core_data[core];
     data.host_context = Common::Fiber::ThreadToFiber();