Performance diagnostics and small wins for title 1

- eden-cli: SDL called SDL_AppIterate back to back, keeping a host core at
  100% polling input; run the main callbacks at 240 Hz.
- EDEN_NX2_IDLE_SPIN_US: optional spin before an idle core blocks (measured:
  no gain on title 1, so off by default).
- EDEN_NX2_SVC_TRACE=<first>:<last>: trace SVCs (with thread ids) for a range
  of presents only.
- MME DMA reads flush GPU-written memory first (never triggered on title 1,
  kept for correctness); render-enable override histogram instead of the
  first-400 log.

Measured on title 1's title screen (RTX 4070 Laptop): GPU ~20% busy, the six
emulated cores ~0.9 host cores in total, Eden's GPU thread 45-70% busy and
largely waiting: on host fences for semaphore acquires (GPU accuracy High
delays every release to host completion), on ASTC upload Finish(), and in a
1 ms poll sleep. gpu_accuracy=Low: ~12.5 -> ~16 fps.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/yuzu_cmd/yuzu.cpp b/src/yuzu_cmd/yuzu.cpp
index f55da5fd61..f44916a2e3 100644
--- a/src/yuzu_cmd/yuzu.cpp
+++ b/src/yuzu_cmd/yuzu.cpp
@@ -172,6 +172,9 @@ struct SdlState {
 };
 
 extern "C" SDL_AppResult SDL_AppInit(void **appstate, int argc, char **argv) {
+    // SDL calls SDL_AppIterate back to back by default, which kept a host core at 100% polling
+    // input; 240 Hz is plenty for input and the key script.
+    SDL_SetHint(SDL_HINT_MAIN_CALLBACK_RATE, "240");
     SdlState* state = new SdlState();
     *appstate = state;