x11-session-research

Status: CLOSED 2026-05-03 with negative result on both campaign axes. Closing remarks (research question, outcome, methodological corrigendum, three legitimate next moves a follow-up could pick up): https://dokuwiki.reauktion.de/doku.php?id=x11_session_research:start. The Phase 0 evidence under phase0_evidence/ and the Phase 0 findings doc are the source-of-truth substrate behind that page; this README left as the on-the-day framing of what the campaign expected to find.

Research question: Does cutting out the KWin compositor enable faster video display of Brave, chromium-fourier, and Firefox — for full SW decoding, and for libva decoding (where possible) — on PineTab2 RK3568?

The operator-supplied mechanism: hantro decodes to NV12; rockchip-drm's overlay plane cannot accept NV12, so on Wayland KWin must own the only NV12-capable plane (Primary, Plane 39) for its compositor framebuffer, which forces a GL-composite of every NV12 video buffer. X11 + non-compositing WM can give the video region directly to Plane 39 (NV12 native) and put the rest of the desktop on Plane 45 (RGB AFBC), avoiding the forced GL-composite. The campaign's load-bearing hypothesis is that this plane-allocation freedom translates into measurable browser-video speedup.

The matrix is (3 browsers + mpv 0.41 as a reference X11-overlay client) × 2 decode paths × 2 sessions = 16 cells (some N/A where libva isn't supported). The mpv cells are run twice each — once with --vo=xv (legacy XVideo overlay) and once with --vo=gpu --gpu-context=x11 (modern DRI3 + XPresent + Mesa GL). See phase0_findings.md § "Experimental matrix" for the full table and the rationale for mpv as reference baseline.

Campaign-contained data discipline

This campaign acquires all its own measurement data from scratch in this session. Numbers, baselines, and verdict thresholds from predecessor campaigns are NEVER imported as binding cells, comparison targets, or success criteria.

Predecessor campaigns are documented for context — what question was asked, what file:line pointers stay valid for source-reading, what tooling/state on ohm carries over. But their measurement numbers (drop counts, perf percentages, Δ_present medians, kwin %CPU values) are reference history only, not data this campaign relies on.

The discipline lesson is concrete: ../kwin_overlay_subsurface/phase8_handover.md closed 2026-05-03 without patch because its Phase 1 binding cells were anchored to a single historical measurement (ohm_gl_fix Phase 0: cage = 7 drops total / 0 post-warmup). That baseline was treated as a stable property of the hardware × software stack and the campaign's whole phase plan was built around closing the gap to it. When the same condition was re-measured at N=3 in the closing session of the campaign, none of the three reps reached 0 post-warmup drops; the median was 26. The campaign's premise didn't hold up to in-session replication, three weeks of phase planning ended at Phase 8 close-out, and the lesson is now feedback_replicate_baseline_first.md in this session's memory.

This campaign acts on that lesson by stronger discipline:

• Every Phase 1 binding cell anchors to data acquired in this campaign's session.
• Predecessor measurements never appear in metrics.csv. Predecessor file:line source-reads, protocol designs, parser scripts may be referenced or re-used as durable substrate.
• The Phase 0 "A1 baseline" rep is not optional. It is the Wayland-with-KWin reference rep acquired at the start of this campaign, against which the X11 cells of the matrix will be compared. The predecessor's matching numbers are not used as a substitute even if they look identical.
• If a measurement instrument behaved one way in a predecessor campaign, that behavior is re-verified here before being relied on (see Phase 0 X11 measurement-tool inventory).

If a measurement in this campaign happens to match a predecessor's number, that's a useful corroboration of reproducibility — but it cannot substitute for in-session acquisition.

Predecessor campaigns

This campaign is the third in a chain on the same hardware target:

1. ../ohm_gl_fix/ — closed 2026-05-02. Diagnosed and patched the Step 1 (libva-v4l2-request) and Step 2 (Chromium WaylandBufferManagerHost overlay-route) issues. Spun off the Wayland-compositor- path question into a separate campaign because that question had a different code surface, upstream, and reviewer culture.
2. ../kwin_overlay_subsurface/ — closed 2026-05-03 without patch (phase8_handover.md). Diagnostic loop terminated at "Phase 0 cage = 0 post-warmup drops floor not reproducible at N=3" — the inherited baseline turned out to be N=1 historical and didn't replicate in-session.
3. This campaign (x11-session-research) — opened 2026-05-03. Tests whether bypassing the KWin compositor via X11 + non-compositing WM avoids the forced NV12 → RGB GL-composite step the predecessor identified as a structural Wayland constraint on rockchip-drm.

Durable substrate from the predecessors that this campaign may read (not import-as-data):

• kwin_overlay_subsurface/phase2_source_findings.md — KWin scanout-promotion archaeology (Plane 39 / Plane 45 format/modifier table on rockchip-drm RK3568); Phase 2-prime Shape C source-read of Display::dispatchEvents and TransactionFence (Wayland-side, doesn't transfer to X11 but illustrates the per-frame dispatch shape).
• kwin_overlay_subsurface/phase3_protocol_prime.md — the measurement-protocol structure (operator-vs-Claude split, pre-registered hypothesis, falsification table, evidence layout). The structural template is reusable. The specific numbers and threshold values are not.
• kwin_overlay_subsurface/scripts/wayland_debug_to_csv.py — parser for libwayland WAYLAND_DEBUG output. Useful for the Wayland cells of this campaign's matrix; an X11 equivalent is yet-to-build.

Hardware target (same as predecessors)

ohm — PineTab2, Rockchip RK3568 (4× Cortex-A55, Mali-G52 MP2, hantro G1/G2 VPU). Kernel 6.19.10-danctnix1-1-pinetab2. Mesa 26.0.5. Currently runs KDE Plasma 6.6.4 Wayland.

For an X11-session campaign, ohm needs an Xorg + non-compositing WM install path verified. As of 2026-05-03, the only confirmed display path on ohm is startplasma-wayland. Phase 0 inventory will catalog what's installed, what'd need installing, and what SDDM-advertised sessions exist.

Carry-overs from predecessor (system state, not data)

Per ../kwin_overlay_subsurface/phase1_evidence/ohm_tooling_revert_log.md:

• qt6-base-fourier 1:6.11.0-3 installed.
• kwin-fourier 1:6.6.4-3 installed.
• CPU governor pinned to performance (was conservative).
• Baloo permanently disabled (Indexing-Enabled=false in ~/.config/baloofilerc).
• drm-info 2.9.0-1 installed.

These were not reverted at the predecessor's close-out. This campaign inherits them as system state, distinct from measurement data. A different system state (e.g. a fresh Plasma session, or the same packages but different uptime) might produce different measurements; this is exactly why in-session baseline acquisition matters.

Non-upstreaming default

Inherited from the predecessors. Bug reports + MRs are explicit operator-tasked decisions, not background process steps.

File map (will grow)

File	What it is
README.md	This file.
phase0_findings.md	Locked motivation + experimental matrix + open questions before Phase 1.
worklist.md	Phase-by-phase task list.
phase0_evidence/ (created when first run lands)	Phase 0 inventory + A1 baseline rep.

Repository

ssh://gitea@git.reauktion.de:2222/marfrit/x11-session-research.git (public). Cloned/pushed via SSH on port 2222 per the home-infra gitea convention.