perf(zaparoo): reduce launcher startup contention

[asturur]

Summary

• add a Zaparoo lifecycle-gated scheduler sleep so Main_MiSTer yields CPU while the launcher is pending or running
• keep the initial Main_MiSTer CRT fb mode write before fork, but remove the post-startup 100 ms rewrite and the 1 s retry rewrite
• snapshot the boot/current framebuffer mode before CRT launch and restore it when returning to stock mode
• replace the agetty/shell trampoline with direct tty2 setup and direct frontend exec
• restore non-blocking spawn finalization so tty readiness polling does not stall input polling
• skip the forced Zaparoo menu RBF reload when MiSTer.ini bootcore already targets the menu RBF, so bootcore can own that load

Validation

• ./docker-build.sh
• git diff --check

Hardware validation still needed

• confirm Main_MiSTer CPU usage drops while frontend starts/runs
• confirm frontend input still works
• confirm OSD overlay opens/responds over frontend
• confirm CRT path shows clean 320x240 framebuffer without stale frames
• [] confirm clean launcher exit restores the boot framebuffer mode

Summary by CodeRabbit

• New Features

  • Added startup timing instrumentation

• Refactor

  • Optimized scheduler with conditional sleep behavior
  • Improved native CRT framebuffer handling and mode restoration
  • Enhanced process spawning and TTY initialization for better core launching

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 00e4118b-ce9f-4d94-936c-7ffed86b39a1

📥 Commits

Reviewing files that changed from the base of the PR and between 92cf0a8 and c634ffc.

📒 Files selected for processing (2)

• support/zaparoo/alt_launcher.cpp
• user_io.cpp

📝 Walkthrough

Walkthrough

The PR refactors the Zaparoo alternate launcher: it replaces bash-script process spawning with direct exec in the child (with CPU affinity, session/TTY setup, and stdio redirection), adds framebuffer mode save/restore for native CRT transitions, introduces TTY deadline and CRT finish timers, adds a zaparoo_alt_launcher_start_for_menu() entry point, gates a scheduler usleep(100) on a new query function, and logs a startup timestamp in main().

Changes

Alt Launcher CRT/TTY/Spawn Refactor + Scheduler Sleep

Layer / File(s)	Summary
New public API declarations support/zaparoo/alt_launcher.h	Declares alt_launcher_scheduler_sleep_enabled() and zaparoo_alt_launcher_start_for_menu() as new exported symbols.
Timer state and framebuffer mode save/restore support/zaparoo/alt_launcher.cpp	Adds global TTY deadline, CRT finish, and native status timer fields plus saved FB mode storage; implements save_current_fb_mode() (reads kernel parameter) and restore_saved_fb_mode() (writes back with fixed fallback).
Native CRT enable/disable/prepare/finish routines support/zaparoo/alt_launcher.cpp	Reworks CRT disable to restore saved FB mode and clear new timers; adds prepare routine saving FB mode, switching to CRT mode, and starting a finish timer; adds finish routine blanking the shmem scan-out buffer and re-enabling status routing; extends state reset to cover new timer fields.
Direct exec spawn replacing bash-script trampoline support/zaparoo/alt_launcher.cpp	Replaces bash-script spawning with exec_launcher_child() that sets env vars, pins to CPU 0, creates a session, attaches TTY via TIOCSCTTY, redirects stdio, and execs the frontend with optional --crt; adds finalize_spawn() for post-fork VT/FB/CRT wiring and menu hiding; refactors alt_launcher_start() to centralize TTY deadline and CRT state.
Runtime polling: CRT finish, TTY deadline, spawn finalization support/zaparoo/alt_launcher.cpp	Updates polling to call the CRT finish routine when its timer expires, route native CRT status via the new timer, reset TTY deadline on child exit, and finalize spawning when TTY is ready or the deadline expires.
Menu entry points, scheduler sleep, and startup log support/zaparoo/alt_launcher.cpp, user_io.cpp, scheduler.cpp, main.cpp	Adds zaparoo_alt_launcher_start_for_menu() and routes it through a new prepare_menu_state helper; user_io_init branches on zaparoo_is_native_core() to call it; adds conditional usleep(100) in the scheduler loop; logs a startup timestamp in main().

Sequence Diagram(s)

sequenceDiagram
  participant user_io_init
  participant zaparoo_alt_launcher_start_for_menu
  participant alt_launcher_start
  participant fork as fork()
  participant exec_launcher_child
  participant finalize_spawn
  participant scheduler_run
  participant alt_launcher_scheduler_sleep_enabled

  rect rgba(100, 150, 255, 0.5)
    Note over user_io_init,alt_launcher_start: Menu bootstrap (native core path)
    user_io_init->>zaparoo_alt_launcher_start_for_menu: zaparoo_is_native_core() == true
    zaparoo_alt_launcher_start_for_menu->>alt_launcher_start: start=true
    alt_launcher_start->>alt_launcher_start: set TTY deadline, CRT fields
  end

  rect rgba(100, 200, 100, 0.5)
    Note over alt_launcher_start,finalize_spawn: Spawn child (direct exec)
    alt_launcher_start->>fork: spawn process
    fork-->>exec_launcher_child: child: setenv, affinity, setsid, TIOCSCTTY, execv
    fork-->>finalize_spawn: parent: switch VT / enable FB or CRT routing, hide menu
  end

  rect rgba(255, 180, 50, 0.5)
    Note over scheduler_run,alt_launcher_scheduler_sleep_enabled: Scheduler sleep gate
    scheduler_run->>alt_launcher_scheduler_sleep_enabled: query
    alt_launcher_scheduler_sleep_enabled-->>scheduler_run: true (TTY deadline or CRT finish active)
    scheduler_run->>scheduler_run: usleep(100)
  end

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related issues

• Track Main_MiSTer launch-side frontend startup wins zaparoo-frontend#247: This PR directly implements the enhancements described in that issue — the alt_launcher_scheduler_sleep_enabled() gate for usleep(100) in the scheduler loop, the CRT setup refactor with the new finish timer, and the replacement of the bash-script trampoline with direct child exec.

Possibly related PRs

• ZaparooProject/Main_MiSTer#1: Both PRs modify the native CRT enable/disable flow and launcher init/polling behavior in support/zaparoo/alt_launcher.cpp.
• ZaparooProject/Main_MiSTer#2: Both PRs add new "init/start for menu" entry points in alt_launcher.* and change menu bootstrap branching in user_io.cpp.
• ZaparooProject/Main_MiSTer#4: Both PRs touch the child process spawn/exec path for the Zaparoo frontend in alt_launcher.cpp.

Poem

🐇 Hop, hop — no more shell script delay,
The child now exec's the right way!
CRT timers tick, TTY deadline set,
The framebuffer mode? Saved — don't fret!
A micro-sleep guards the scheduler's beat,
And a menu start makes the launch complete. 🌟

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(zaparoo): reduce launcher startup contention' directly and concisely summarizes the primary objective of the pull request—reducing CPU contention during Zaparoo launcher startup through performance optimizations like scheduler sleep and non-blocking spawn finalization.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/zaparoo-launcher-startup

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[asturur]

i want to know when main start during boot. is the time we want to save before this line? if yes we should stop looking here.

[asturur]

The reason for those changes would be to be a bit faster, but also to enable a way from frontend to override mister and menu with our forks, and go back to normal with a toggle, restoring backups.

[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@support/zaparoo/alt_launcher.cpp`:
- Around line 140-181: The s_saved_fb_mode_valid flag is never cleared after
restore_saved_fb_mode() completes, causing save_current_fb_mode() to exit early
on subsequent calls due to its initial guard check. In the
restore_saved_fb_mode() function, after the fprintf and fclose calls that write
and close the framebuffer mode file, add s_saved_fb_mode_valid = false to reset
the flag so that the next CRT session will capture a fresh framebuffer mode
snapshot instead of reusing the stale original one.

In `@user_io.cpp`:
- Around line 1472-1473: The native-core boot path at line 1473 calls
zaparoo_alt_launcher_start_for_menu(), but this function should be mutually
exclusive with zaparoo_alt_launcher_init_for_menu() which is called later at
line 1549. Currently both execute in sequence, resetting launcher state after
spawn setup. Add a guard condition at line 1549 where
zaparoo_alt_launcher_init_for_menu() is called to prevent its execution when the
native-core path was taken (i.e., when zaparoo_is_native_core() was true and the
other conditions at line 1473 were met). This ensures only one of the two
functions executes per boot cycle.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 73f2368f-763f-4107-9844-c13c9439cacc

📥 Commits

Reviewing files that changed from the base of the PR and between 7a05c05 and 92cf0a8.

📒 Files selected for processing (5)

• main.cpp
• scheduler.cpp
• support/zaparoo/alt_launcher.cpp
• support/zaparoo/alt_launcher.h
• user_io.cpp