ASTC transcode pool: an eighth of the hardware threads (at least 2)

With half (8 on a Ryzen 7 8845HS), re-compressing streamed ASTC textures to
BC3 took ~3.5 cores away from the six emulated cores and the GPU thread.
Title 1 attract loop, 65-150 s: 8 threads 16.0 fps, 4 threads 12.6, 2
threads 18.9 (scene noise is large). EDEN_NX2_TRANSCODE_THREADS overrides.

1 files changed, 11 insertions, 2 deletions

diff --git a/src/video_core/textures/workers.cpp b/src/video_core/textures/workers.cpp
index a1953c4bf4..6922634e30 100644
--- a/src/video_core/textures/workers.cpp
+++ b/src/video_core/textures/workers.cpp
@@ -4,13 +4,22 @@
 // SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include <cstdlib>
+
 #include "video_core/textures/workers.h"
 
 namespace Tegra::Texture {
 
 Common::ThreadWorker& GetThreadWorkers() {
-    static Common::ThreadWorker workers{(std::max)(std::thread::hardware_concurrency(), 2U) / 2,
-                                        "ImageTranscode"};
+    // An eighth of the hardware threads (at least 2): with half, re-compressing streamed ASTC
+    // textures took ~3.5 cores from the emulated CPU cores and the GPU thread on an 8-core
+    // laptop. EDEN_NX2_TRANSCODE_THREADS=<n> overrides.
+    static Common::ThreadWorker workers{[] {
+        if (const char* text = std::getenv("EDEN_NX2_TRANSCODE_THREADS")) {
+            return (std::max)(static_cast<u32>(std::strtoul(text, nullptr, 10)), 1U);
+        }
+        return (std::max)(std::thread::hardware_concurrency() / 8, 2U);
+    }(), "ImageTranscode"};
     return workers;
 }