# Work items — x11-session-research ## Governing rule (every phase) **Campaign-contained data acquisition.** Every measurement this campaign relies on is acquired in this campaign's session. Predecessor numbers are reference history, never imported as binding cells, comparison targets, or success thresholds. The A1 baseline below is not optional — it is the in-session Wayland anchor against which X11 cells are compared. See `phase0_findings.md` § "Campaign-contained data discipline" and `README.md` § "Campaign-contained data discipline" for the full rule and the predecessor lesson that motivated it. ## Phase 0 — substrate + research question + inventory **Status: IN PROGRESS.** Motivation LOCKED 2026-05-03 in `phase0_findings.md` § "Research question". Pre-Phase-1 inventory and baseline-anchor work below. - [x] Predecessor close-out summarised. Substrate doc lists what transfers from `kwin_overlay_subsurface` and what's Wayland-specific (KWin source-reads don't transfer to X11 path). - [x] **Research question locked.** "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?" - [x] **Mechanism captured.** Operator-supplied insight 2026-05-03: hantro emits NV12, rockchip-drm overlay plane doesn't accept NV12, so KWin must own the only NV12-capable plane (Primary, Plane 39) and forces GL-composite of every NV12 buffer. X11 + non-compositing WM can give the video region directly to Plane 39 and put rest of desktop on Plane 45 (RGB AFBC) — hardware-blended, no GL-composite. - [x] **Experimental matrix drafted.** 3 browsers × 2 decode paths × 2 sessions = 12 cells (some N/A where libva isn't supported). See `phase0_findings.md` § "Experimental matrix". - [ ] State snapshot of ohm under current Plasma Wayland — the campaign-start *before* photo. Unattended-tractable via SSH. Captures package versions, kernel, kwin_wayland PID + cmdline, governor, services, browser binary versions, test asset paths, thermal_zone temps. - [x] Inventory of available X11 paths on ohm. Captured 2026-05-03 in `phase0_evidence/x11_inventory_2026-05-03/` (raw `02_x11_paths.txt` + summary `inventory.md` § "Deliverable 2"). Verdict: xorg-server 21.1.22 + Mesa 26.0.5 / Panfrost healthy, modesetting (in-server) is sole DDX, only `kwin_x11` WM installed today, six WM candidates available in extra, Plasma X11 + Plasma Wayland + Weston are the SDDM-advertised sessions. Operator action: `pacman -S` a non-compositing WM (recommend openbox) and create/switch to its SDDM session before without-KWin cells can run. - [x] **Browser X11-overlay-path inventory.** Captured 2026-05-03 in `phase0_evidence/browser_overlay_inventory_2026-05-03.md` + acquired-source subtree `phase0_evidence/chromium_ozone_x11_2026-05-03/` (Chromium 147 from `chromium-builder` LXD CT on boltzmann via the his subagent). **Decisive verdict at the source level:** Chromium ozone-x11 instantiates `StubOverlayManager` (`ozone_platform_x11.cc:262`) — no overlay candidates ever promoted; Brave 147 + chromium-fourier 149 inherit this unchanged (their patches don't touch Ozone). Firefox 150 `WindowSurfaceX11{,Image,SHM}` are RGB-only (zero NV12 / dmabuf / DRI3 / XPresent references in any X11-surface file). **No browser in the matrix has a code path to hand NV12 to the X server for plane scanout.** Only mpv `--vo=xv` does; mpv `--vo=gpu --gpu-context=x11` is the same GL-composite shape as the browsers. Implication: campaign's load-bearing hypothesis is structurally weakened — the X11-vs-Wayland delta the matrix will measure for browsers is "browser-side GL composite + X-scanout-of-RGB" vs "browser-side GL composite + KWin-RGB-recomposite + scanout". mpv-xv becomes the matrix's only direct test of the original mechanism. Runtime-engagement probe deferred to Phase 1 first rep (design sketched in the inventory doc). - [x] **mpv added as 4th matrix client** 2026-05-03. Two cells (full SW, libva/v4l2request) × 2 sessions × 2 VOs (`--vo=xv` and `--vo=gpu --gpu-context=x11`) = 8 reference data points. README + `phase0_findings.md` § "Experimental matrix" updated; matrix grew from 12 → 16 cells (+8 mpv VO sub-points). mpv 0.41.0 already installed via predecessor (see `phase0_evidence/x11_inventory_2026-05-03/02_x11_paths.txt`). - [x] Inventory of X11-side measurement instruments. Captured 2026-05-03 in `phase0_evidence/x11_inventory_2026-05-03/` (raw `04_measurement_instruments.txt` + summary `inventory.md` § "Deliverable 4"). Live X server supports all 7 needed extensions (Composite, DAMAGE, DRI3, Present, RANDR, SYNC, XVideo). Tools installed: xprop, xdpyinfo, xset, glxinfo, drm_info, perf, mpv, libxcb-present. Tools missing-but-in-extra: xrandr CLI, xev, xinput, xwininfo, xkill, sysprof — one `pacman -S` away. AUR-only: X-protocol `xtrace` (the `/usr/bin/xtrace` from glibc is a syscall tracer, unrelated); optional, matrix doesn't strictly need protocol traces. perf_event_paranoid=2 — set to 1 once for unattended runs. - [ ] **A1 baseline: in-session Wayland-with-KWin anchor.** Mandatory per the governing rule. 3 reps minimum (variance is a real concern on this hardware per the predecessor data) of a `kwin_timing_nodebug`-equivalent run on the current Plasma Wayland session, captured into `phase0_evidence/wayland_baseline_repN/`. **This is the only Wayland baseline this campaign uses.** No predecessor number substitutes for these reps even if the predecessor measured an "identical" condition. The 3 reps also surface the session-internal variance up front, so Phase 1 thresholds aren't drawn against a single sample. ## Phase 1 — binding cells + measurement protocol **Pending Phase 0 inventory + A1 baseline anchor.** Phase 1 lock will produce `phase1_lock.md` with: - Binding cells per matrix cell (effective_fps, drops_total, drops_post_warmup, end-to-end-latency-if-testable, compositor+browser CPU at steady state). - The clear-pass / clear-fail thresholds: what "X11 is faster" means quantitatively. Thresholds are drawn from the A1 Wayland baseline acquired in *this* campaign — not from predecessor numbers. Provisional shape (numbers TBD from A1): a matrix cell counts as "X11 faster" if its effective fps exceeds the campaign's same-cell Wayland median by a margin larger than the campaign's same-cell Wayland IQR, and its drops_post_warmup is materially below the same cell's Wayland median. - The measurement protocol per matrix cell, including how the X11 sessions are entered and how the browser is launched with libva forced on/off. Mirrors the structure of `kwin_overlay_subsurface/phase3_protocol.md`. ## Phase 2-onwards Pending. ## Discipline carry-overs from `kwin_overlay_subsurface` - *Campaign-contained data acquisition* — see governing rule at the top of this file. The strongest version of the predecessor's "replicate the baseline first" lesson: **don't import predecessor data at all**, acquire it fresh. - *Phase discipline* — no patches before source-read is documented. Re-scoping must be honest about deferral target. - *Non-upstreaming default* — bug reports + MRs are explicit operator-tasked decisions. - *Memory persistence rule* — when this campaign reaches its diagnostic terminal state (success or honest closure), update `project_campaign_overview.md` and add any new feedback memory worth carrying forward to the next campaign.