From 3f509ebc5c8445ac8a8cba08a76690c3b15c90e6 Mon Sep 17 00:00:00 2001
From: MechaCat02 <fabian@diekaulbachs.de>
Date: Sun, 5 Jul 2026 14:16:12 +0200
Subject: [PATCH] [iterate-4C] --ui: make threaded GPU the default (was opt-in
 XENIA_UI_GPU_THREAD)
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Measured ~5× faster boot under --ui (~12 → ~63 MIPS) by moving the per-frame
PM4 drain (draws, YUV texture decode, resolves) + UI publish off the emulation
thread onto the GPU worker — canary's async-command-thread model. User-confirmed
visuals identical to the inline path (splash + intro video render correctly).

Flip the default: `--ui` now uses the threaded GPU backend. Opt back to inline
with `--gpu-inline` or `XENIA_UI_GPU_INLINE=1`. The deterministic golden path
already passes `--gpu-inline`, so goldens are unaffected (n2m re-checked MATCH).
`XENIA_UI_GPU_THREAD` retained as a no-op alias. Headless default (M1.9 threaded)
unchanged.

Note: threading the GPU only helps GPU-bound phases (boot). The intro VIDEO is
CPU-bound on multi-threaded 720p-YUV software decode (FP-arith-heavy, mostly JIT
fallback), so it stays ~real-video-length; that needs the multi-core / native-FP
levers, not GPU threading.
---
 crates/xenia-app/src/main.rs | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/crates/xenia-app/src/main.rs b/crates/xenia-app/src/main.rs
index ba79147..ff7e297 100644
--- a/crates/xenia-app/src/main.rs
+++ b/crates/xenia-app/src/main.rs
@@ -966,19 +966,23 @@ fn cmd_exec_inner(
             let v = v.trim().to_ascii_lowercase();
             v == "1" || v == "true" || v == "yes"
         });
-    // A.5 — opt-in threaded GPU under `--ui`. Off by default: `--ui` still
-    // forces the inline backend (the safe, milestone-verified path). When
-    // `XENIA_UI_GPU_THREAD=1` is set alongside `--ui`, the GPU command
-    // processing + per-swap UI publish move to the worker thread, freeing the
-    // emulation thread from the ~12 ms/frame inline PM4 drain. See
-    // `run_with_ui` (hook install) and `GpuSystem::run_ui_publish`.
-    let env_ui_thread = std::env::var("XENIA_UI_GPU_THREAD")
+    // A.5 — threaded GPU under `--ui`, now the DEFAULT. The GPU command
+    // processing + per-swap UI publish run on the worker thread, freeing the
+    // emulation thread from the ~12 ms/frame inline PM4 drain — measured ~5×
+    // faster boot under `--ui` (~12 → ~63 MIPS), visuals confirmed identical to
+    // the inline path. See `run_with_ui` (hook install) and
+    // `GpuSystem::run_ui_publish`. Opt back to the inline backend with
+    // `--gpu-inline` or `XENIA_UI_GPU_INLINE=1` (the deterministic golden path
+    // already uses `--gpu-inline`, so goldens are unaffected). `XENIA_UI_GPU_THREAD`
+    // is retained as a no-op alias for back-compat.
+    let env_ui_inline = std::env::var("XENIA_UI_GPU_INLINE")
         .ok()
         .is_some_and(|v| {
             let v = v.trim().to_ascii_lowercase();
             v == "1" || v == "true" || v == "yes"
         });
-    let ui_threaded = ui && env_ui_thread;
+    let ui_inline_optout = gpu_inline || env_inline || env_ui_inline;
+    let ui_threaded = ui && !ui_inline_optout;
     let force_inline = gpu_inline || env_inline || (ui && !ui_threaded);
     let force_thread = gpu_thread || env_thread || ui_threaded;
     let use_threaded = if force_inline {