DroidDeck - Performance findings

Why DroidDeck 0.2.0 ran slower than WinNative and Bannerlator for many people, what was found, what was changed, what was measured, and what is still open. Written 2026-09-29 from the Discord reports, the GitHub issues, and a day of measurement on an AYN Thor (SD 8 Gen 2, Adreno 740). Companion to progress-log.md.

What people reported

Discord (#general, 2026-09-26 to 09-29). The same game at ~90-100 fps in WinNative and ~30-40 in DroidDeck 0.1.7, ~25 in 0.2.0 (Adreno 732); "15 fps in a 2D Unity game" on an 8 Elite while Bannerlator's Steam client is fine; "20 fps / 7 fps in the Steam client, all renders on CPU" on an Adreno 8xx; Bannerlator locked at 120 fps where DroidDeck is not; "less performant, more compatible" as the usual summary.
#65 - the best report: Silksong at 85-90 fps on 0.1.5 and 37-50 on 0.2.0 on a Fold8, GPU 82% busy vs 16%, proot 3-5x busier, the game's main thread waiting on futex and the wineserver pipe. History table: 90 (0.1.5), 103 (0.1.6), 58/110/48 (0.1.7), 47-50 (0.2.0).
#64 - Samsung's SSRM clamps CPU/GPU to ~60% in a session (Tab S8 Ultra). A platform limit, separate from everything below; no sanctioned way around it found.

Cause 1: proot's kompat extension traced every hot syscall (fixed, PR #81)

--kernel-release (added 2026-09-25 to give the guest the DroidDeck hostname, 53ce764) loads proot's kompat extension. Its filter list includes futex, epoll_pwait, fcntl, pselect6, pipe2, eventfd2, socket, so each of those from every guest thread stopped in the single tracer, and it drops AT_SYSINFO_EHDR on every execve, so glibc ran without the vDSO. With the real kernel release passed, every one of those handlers is a no-op. Patch tools/proot/patches/0011-kompat-utsname-only.patch traces only uname/sethostname/setdomainname in that case.

Guest micro-benchmarks (same rootfs, proot with vs without the patch):

	old + `--kernel-release`	patched	no flag at all
futex ping-pong	465 us	102 us	96 us
`epoll_pwait(0)`	60 us	0.87 us	0.8 us
`fcntl(F_GETFL)`	40-107 us	0.39 us	0.38 us
`clock_gettime`	0.34 us	0.19 us	0.11-0.19 us

A-B-A in Once Upon a KATAMARI (standing still, only libproot.so swapped): +2-5% fps, proot CPU ~56% -> ~35%. Small there because Katamari is limited by translated game code; sync-heavy games should gain more.

Cause 2: a crash-looping mangoapp in Deck mode (fixed, PR #81)

gamescopereaper --respawn -- mangoapp restarts the overlay the moment it exits, with no backoff. On a build whose session preload lacked the System V message queue emulation, mangoapp died right after creating its swapchain and was restarted 132 times in ~2.5 minutes; each restart is a full exec under proot and the Steam menu itself lagged. Local builds that skip rebuilding libblsession.so hit this; CI builds do not. The wrapper (tools/mangoapp/mangoapp) now parks after more than 5 starts in 60 s.

What Bannerlator and WinNative do differently

Read from their sources and a device that has Bannerlator installed:

Same proot patches (0001-0009 from WinNative); the Steam client mode uses the same Valve ARM64 Proton, so the same server-side Wine synchronisation (wineserver: using server-side synchronization in every session log here). No structural gap remains once kompat is out.
Defaults differ. Bannerlator ships Deck mode off (it notes Steam Input takes the pad and breaks games), never passes -steamos3, does not set gamescope's realtime queue, runs xalia. WinNative defaults to TU_DEBUG=noconform,sysmem, ZINK_DEBUG=compact, FEX PERFORMANCE_TSO, vkd3d shader model 6_6, and never turns on sustained performance mode.

Changes on `perf/steam-client-parity`

xalia skipped by default (it ran ~10% of a core beside every game under FEX).
gamescope realtime Vulkan queues: new toggle (Performance -> Client interface), off by default.
Microphone off by default; no permission prompt at start-up.
FEX default preset PERFORMANCE_TSO; TU_DEBUG=noconform always (plus sysmem for the 710-720 drivers or when chosen); ZINK_DEBUG=compact; vkd3d shader model 6_6, feature level left to vkd3d-proton.
Sustained performance mode is opt-in (Performance page); PerfMode logs "sustained mode off".
The session gets the panel's fastest mode's refresh rate instead of the rate at the moment the surface arrived.
Session polling without forks: the fill-screen and stop watchers wait on a FIFO read timeout and read files with builtins; the redistributable seeder and the compat registrar (Python) start only when a prefix or the Steam config actually changed, not every 5-15 s.
The Steam page shows the saved Deck mode before the Performance page has been opened (it showed "off" while the session ran Deck mode with mangoapp).
tools/build_local.sh: caches its pinned downloads, skips an unchanged proot build, and says why it rebuilds the Docker image; a warm build is ~30 s (it used to hang on a registry fetch when the daemon briefly reported the image missing).
Turnip sysmem was made a default and then reverted: it gained nothing on an Adreno 740.

How it was measured

fps: BannerWayland [stats] lines in logcat (adb logcat -s BannerWayland:I), every 10 s. No su, no process on the device. The "screen" number counts presents and runs ~1.5x the game's own overlay counter in Alan Wake (60 vs 38-40): compare like with like, and read the overlay for the game's real rate.
Scene: Alan Wake's American Nightmare, first gameplay spot ("Secure the primary pipes"), standing still. Reached without touching the screen: ~/.bl-autolaunch is ignored once Steam is up, so the game is started with steam steam://rungameid/<id> from a second proot invocation (the client forwards it), and A is pressed with sendevent on the device's own gamepad node (/dev/input/event12) - the app only forwards events from a real controller device, so adb shell input presses are dropped.
Thermals: the SoC reaches ~92-95 C in any run, so each run starts only after the CPU zones are under 55 C. A one-shot comparison made hot was misleading (the new build read 52-54 fps then, 58-61 cooled).

Alan Wake, cooled starts, fan at max, 60 s each (screen counter, six 10 s samples):

Build	screen fps	game overlay	proot CPU	wineserver CPU
`main` (kompat fix, old defaults)	56.9-58.6 (avg 57.7)	39	~39%	~30%
new defaults	58.6-61.5 (avg 59.6)	38-39	~27%	~34%
new defaults, sysmem off	59.3-62.9 (avg 61.1)	38	-	-

Read: the defaults are worth at most a few percent here and inside the run-to-run noise (about +-1.5 fps). The game's own frame rate stayed at 38-40 with CPU ~65% and GPU ~56-60%, so this scene is bound by something none of these settings touch.

Open leads, biggest first

Wine synchronisation. Proton 11 dropped esync; fsync needs futex_waitv, which Android's app sandbox blocks even on a 6.12 kernel; ntsync is not in Android kernels. Every lock and event is a pipe round trip to wineserver (30-34% CPU in Alan Wake, 18% of the main thread blocked in read() in #65). Winlator-family apps run esync, which needs only eventfd and poll. Restoring esync in the ARM64 Proton is the largest likely win and the largest piece of work; emulating futex_waitv in proot puts every wait back through the tracer and is probably a dead end.
The game's main thread under FEX. Alan Wake's process uses 139-178% CPU with neither the CPU nor the GPU saturated overall. FEX settings beyond the presets (SMC checks, multiblock, TSO variants) are worth a sweep on a game whose main thread is the limit.
#65's other 0.1.5 -> 0.2.0 differences, untested: the fake power_supply tree, BL_HDR/DXVK_HDR, the output width (1280 -> the panel's shape), FEX_TSOENABLED (1 -> 0), the tracer binary. Their Silksong setup is sync-heavy and is the best test of the kompat fix.
gamescope calls XQueryPointer on every vblank in the Steam UI (patch 0100); query only when a gamepad cursor move is pending. Needs a new pinned gamescope release.
Heavy games on a fresh install. Metal Gear Solid V: Ground Zeroes sat on Steam's launch splash for 5+ minutes with wineserver at ~50% CPU and the GPU at 12% (no window ever appeared); Bulletstorm took ~4.5 minutes to reach its first logo, the game process at 45-105% CPU and the GPU at 9%, and the session ended a minute later. Neither reached a scene worth measuring. Both are first launches (redistributable install scripts, shader work), and a wineserver spinning at 50% while a game shows nothing is itself the server-side synchronisation cost of lead 1.
Reports not yet reproduced: software rendering on Adreno 8xx ("all renders on CPU"), Deck mode using most of the RAM, Samsung SSRM clamping (#64), two DroidDeck packages both holding a session.
Smaller: proot tracer pinned to a big core (Max's note: no core wake-up lag), steamrtarm64 on Proton's LD_LIBRARY_PATH, the always-on wake and Wi-Fi locks, ADPF hints fed frame intervals instead of work time.

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