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docs: I5's clean scroll comparison between Compose and iris, one session

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Same sandbox session content, same emulator, EMU_GPU=software: Compose
(debug, in-app report) 1102 frames/99.0% late/p50 33.8ms/p99 79.5ms vs
iris (release -- debug SIGSEGVs on this emulator) FrameReport 299
frames/94.65% janky/p50 79.1ms/p99 117.8ms (repeat: 233/94.42%/p50
109.3ms). Ticks I5 [x]; states plainly what's not comparable (build
profile forced asymmetric, three different jank definitions, both are
software-rasterised emulator numbers). The two "zero frames" attempts
that preceded the clean runs traced to this session's own script bug
(a cd into /tmp changed which emulator ui-trace targeted), not a
reproduction of the previously-suspected touch-delivery dropout; a
sampler ran the whole session and saw load rise during the gesture
without correlating to any failure. DECISIONS.md's DEFERRED item gets
the same table so Iris can decide iris-vs-Masonry from it -- that
choice is left to her.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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irisandClaude Fable 5.1 committed 2026-09-05 15:21:45 -04:00
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@@ -36,24 +36,26 @@ session spending an afternoon on them again.
## Where things stand (2026-09-05)
- **iris now has its own frame-timing report and a confirmed on-device
long-press-drag, 2026-09-05, later the same day (I5's box still `[~]`,
not `[x]` -- see I5's own box for exactly why).** `iris_core::FrameReport`
(new) times every frame from `render()`'s redraw start to after
`queue.submit`+`present()`, exposed as two named on-screen controls, and
a new `ui-trace holddrag` action (in `emulator-tools`) can finally
produce a real hold-then-drag touch sequence. Both were driven for
real: long-press-then-drag-to-select is confirmed on-device (logcat plus
a screenshot of the highlighted selection), and `FrameReport` captured a
real number from a real touch-drag (`frames=34 janky%=61.76 p50=26.5ms
p90=48.0ms p99=98.1ms worst=98.1ms`). **What's still missing**: a clean,
single 24-swipe loop comparable to Compose's own number -- gestures
against this checkout's `EMU_GPU=software` emulator intermittently
delivered zero touch input during this pass, for a reason named but not
yet confirmed (candidate: the emulator's own software rasterisation,
measured at ~78% of a CPU core continuously, starving synthetic touch
delivery under load). Next: a sampler running *during* a failing gesture
to confirm or rule out that candidate, then the clean comparable loop.
- **I5 is now `[x]`: a clean, single-session, like-for-like 24-swipe
scroll comparison between Compose and iris exists, 2026-09-05.** Same
sandbox session content for both apps, same emulator, `EMU_GPU=software`
(a second pair under `-gpu host` not yet taken). Headline: Compose
(debug build) 1102 in-app-reported frames, 99.0% late, p50 33.8ms/p90
50.6ms/p99 79.5ms; iris (**release** build -- debug `SIGSEGV`s on this
emulator, I4's finding) `FrameReport` 299 frames, 94.65% janky, p50
79.1ms/p90 98.6ms/p99 117.8ms/worst 212.6ms (repeat run: 233 frames,
94.42%, p50 109.3ms). **Not a clean apples-to-apples number**: different
build profiles (forced, not chosen), different jank definitions/frame
populations across the three measurement sources, and both are emulator
numbers under software rasterisation -- all stated plainly in I5's own
box, "Clean scroll comparison, 2026-09-05," which also has the
sampler timeline (load rose during the gesture but did not correlate
with a failure this pass) and the dropout finding (this pass's own
script bug -- `cd`ing into `/tmp` changed which emulator `ui-trace`
targeted -- not a reproduction of the previously-suspected touch-
delivery starvation). `DECISIONS.md`'s DEFERRED item has this table's
numbers for Iris to decide from; the iris-vs-Masonry choice itself is
still hers to make, not decided here.
I5's own box, "Update, 2026-09-05, later the same day" has the full
account.
- **I5's Android integration is done and measured, 2026-09-05.** The
@@ -2344,23 +2346,19 @@ silently on real hardware.
time it was hit (mid-session, after adding an unrelated temporary
log line forced a dev rebuild) and cost real time to separate from
the actual touch-dispatch question being chased at the time.
- [~] **I5 — the transcript screen in iris (2026-09-05, updated later the
same day). The widget-tree half and the Android integration are
both built and confirmed working on-device (real server, real
scrolling, real touch-drag pan, tap-by-name), iris now has its own
frame-timing instrumentation (`FrameReport`) and produced a real,
measured number from a real on-device touch-drag, and long-press-
then-drag-to-select is now confirmed on-device too (both by logcat
and by a screenshot showing the highlighted selection); still `[~]`
rather than `[x]` because the frame-time number obtained is not the
clean, single 24-swipe loop comparable to Compose's -- gestures
against this checkout's `EMU_GPU=software` emulator intermittently
produced zero frames for reasons not yet isolated (candidate: the
emulator's own software rasterisation measured at ~78% of a CPU
core, continuously, which may be starving synthetic touch delivery
under load -- not yet confirmed with a sampler running during the
failing gesture). See "Update, 2026-09-05, later the same day" and
"What remains" near the end of this box.**
- [x] **I5 — the transcript screen in iris (2026-09-05, updated later the
same day, and again 2026-09-05 with the clean scroll comparison).
The widget-tree half and the Android integration are both built and
confirmed working on-device (real server, real scrolling, real
touch-drag pan, tap-by-name), iris has its own frame-timing
instrumentation (`FrameReport`), and long-press-then-drag-to-select
is confirmed on-device (both by logcat and by a screenshot showing
the highlighted selection). Ticked `[x]` now that a clean,
single-session, like-for-like 24-swipe comparison against Compose
exists -- see "Clean scroll comparison, 2026-09-05" near the end of
this box for the numbers, what is and is not comparable between the
two, and the dropout finding (this pass's own script bug, not a
reproduction of the emulator touch-delivery candidate below).**
**Where it lives.** `iris/transcript-ui/` (new workspace member,
`[lib]`), the same shape as `iris/tabs-ui`: generic over `Rsc:
@@ -2861,6 +2859,159 @@ silently on real hardware.
DEFERRED item is updated with this session's numbers and the
touch-delivery caveat rather than a decision made here.
**Clean scroll comparison, 2026-09-05, one session, this checkout's
emulator, `EMU_GPU=software` only (the mode the existing Compose
figure above was taken under; a second pair under `-gpu host` was
not reached this pass -- see "Not attempted" below).** New content
for a fair pairing: a fresh sandbox session (`app/ui-sandbox.sh
spawn benchsession`, id `4d21d4a0d38f79fd`) with 30 identical sent
messages, each one heading/bold/italic/inline-code/link/list/fenced-
code paragraph, so both apps scroll the exact same bytes -- neither
of the two sessions quoted in this box's earlier passes (`8920378e
7167ebcd`, 40 msgs; `c76b71d017a54589`, 120 msgs) was reused, since
neither app had touched it. A sampler
(`date`/`/proc/loadavg`/`/proc/pressure/{cpu,io}`/top-5-by-CPU every
2s to `/tmp/iris-bench-sampler.log`) ran for the whole session,
started before either app was built, per the standing rule against
diagnosing a timing question from measurements taken after the
fact.
| app | build | GPU mode | frames | janky % | p50 | p90 | p99 | worst |
|---|---|---|---|---|---|---|---|---|
| Compose (in-app report) | debug | software | 1102 | 99.0% late | 33.8ms | 50.6ms | 79.5ms | -- |
| Compose (`dumpsys gfxinfo`) | debug | software | 1499 | 21.15% (95.66% legacy) | 32ms | 48ms | 150ms (99th) | -- |
| iris (`FrameReport`, run A) | **release** | software | 299 | 94.65% | 79.1ms | 98.6ms | 117.8ms | 212.6ms |
| iris (`FrameReport`, run B, repeat) | **release** | software | 233 | 94.42% | 109.3ms | 130.8ms | 147.1ms | 150.5ms |
Exact commands: Compose via `app/transcript-bench.sh` unmodified
(`open_session` then `copy_render_report` bracketing the standard
24-swipe/6-cycle loop, `dumpsys gfxinfo com.example.aiapp reset`
taken immediately before for the second row). iris via the same
24-swipe loop code -- extracted verbatim from
`transcript-bench.sh`'s `DO=""` .. `eval ui-trace record` block with
`sed`, not retyped, since `transcript-bench.sh` itself is Compose-
specific (opens by session title through the Compose app's own UI)
and could not be called directly -- bracketed by `ui-trace record
--do "tap 'Reset frame report'"` and `--do "tap 'Frame report'"`
(iris's own two named controls, I5's earlier "Update" section),
reading the result from `logcat`'s `iris frame report:` line.
**What each number counts, stated because the three are not the
same measurement.** Compose's in-app report times its own
Compose-internal phases (`total` = the full frame from Choreographer
callback to submit) and calls a frame "late" past a 16.7ms budget --
a stricter, self-reported definition. `dumpsys gfxinfo`'s "janky"
is Android's own HWUI/BLAST deadline-miss accounting, a different
threshold and a different frame population (it free-runs over
`Total frames rendered`, which includes frames from opening the
session and the report dialog, not only the swipe window -- hence
1499 vs. the in-app number's 1102). iris's `FrameReport` times
wall-clock from `render()`'s redraw start to after `queue.submit`+
`present()` -- i.e. iris's own render path only, nothing above the
GPU submit and nothing from Android's compositor -- confirmed
independently useless for iris via `dumpsys gfxinfo
dev.iris.android.demo`, which reported 1 total frame for the whole
run (unchanged from the earlier pass's finding: HWUI has no
visibility into a `wgpu`-drawn `SurfaceView`).
**Not comparable, stated plainly:**
- **Build profile differs by necessity, not choice.** Compose is
the **debug** variant (AGENTS.md's own bench-script requirement,
"the emulator scripts stay on the debug build"). iris is
**release** because I4's box already found the debug/dev profile
`SIGSEGV`s in this emulator's Vulkan loader the moment `wgpu`
creates a bind-group layout (`InstanceFlags::from_build_config()`
turns on debug object-labelling, which crashes against
`vulkan.ranchu.so`) -- there is no debug iris number to quote on
this rig. A release build is typically *faster* than debug, so
this asymmetry very likely understates how much worse than
Compose iris's own number would look built the same way Compose's
is, not the reverse.
- **The jank definitions and frame populations differ**, per the
paragraph above -- none of the three numbers is measuring the
same thing, so reading "94.65% > 21.15%" as "4x worse" is not
sound; only the general shape (iris's frames take longer, both by
its own accounting and by eye in the screenshots) transfers.
- **Both figures are emulator numbers under software rasterisation
(`EMU_GPU=software`/SwiftShader), not phone numbers**, per
AGENTS.md's and `this-machine-android`'s standing rule -- restated
because it applies doubly to iris's own number here: SwiftShader
is CPU-bound by design, and Compose's *own* in-app report shows a
14.6-22.2ms `swap` phase and a 20.8-33.9ms `gpu` phase alone (more
than the entire 16.7ms budget) under the same GPU mode, so a
software-rendering iris number well above 16.7ms is expected
going in and should not be read as an iris-specific defect
without a `-gpu host` pair to compare against.
**Where iris's time goes, from `FrameReport`/logcat -- not
optimised, per this task's own instruction, only described.** Two
things were checked because they were checkable without new
instrumentation: (1) **iris does not redraw while idle** --
`adb logcat -c` followed by a 3s settled wait produced *zero*
`iris::android::view: render()` lines, both before and after a
swipe; the render-per-frame spam only appears during and briefly
after a gesture (visible inertial settle), so there is no idle-
redraw tax to find here, unlike the composer-inset bug AGENTS.md
records for the Compose app. (2) **a swipe frame does not appear to
relayout the whole list** -- consecutive `render()` log lines during
a swipe show `active=88` falling to `83`, `78`, `73`, ... one small
step per frame, consistent with I3's virtualised list culling
widgets that scrolled out of the viewport rather than re-measuring
everything each frame (a full-list relayout would show `active`
constant at the total row count, not shrinking through it). Neither
observation isolates *where* the remaining ~80-150ms/frame actually
goes past those two rule-outs -- the leading remaining candidate is
the swapchain present/GPU path itself under SwiftShader's CPU
rasterisation, per the "not comparable" point above, but that was
not measured directly this pass (no per-phase breakdown inside
`FrameReport` the way Compose's report has `measure`/`place`/
`record`/`swap`/`gpu`).
**The dropout finding, corrected from earlier in this box: this
pass's own script bug, not a reproduction of the touch-delivery
candidate.** Of 3 planned attempts, the first 2 produced `iris frame
report: no frames recorded` -- but tracing it down found the cause
in this session's own tooling, not the emulator: the swipe loop was
extracted from `transcript-bench.sh` into a temporary wrapper script
that `cd`'d into `/tmp` before invoking `ui-trace`, and `ui-trace`/
`adb` here derive *which emulator to target* from the current
directory's basename (the per-checkout-AVD rule) -- from `/tmp` that
resolved to a nonexistent checkout named "tmp", `ui-trace` refused
immediately, and the wrapper's `set -eu` aborted the whole loop
before a single swipe was sent. Once the wrapper was fixed to run
from inside this checkout, the next **two** attempts (runs A and B
in the table above) both succeeded on the first try, each with a
confirmed screenshot-hash difference showing real scrolled content.
So this session did not reproduce the previously-documented
intermittent zero-touch phenomenon -- but two successes out of two
*valid* attempts is also too little evidence to say it is gone;
the earlier session's drops happened with a correctly-targeted
device, which is a different failure than the one found here.
**Sampler timeline**: `/tmp/iris-bench-sampler.log` shows
`/proc/loadavg` and the runnable-process count rising from an idle
baseline (~0.3-1.7 load, 0-4 running) to ~2.5-2.9 load and 11-23
running during the swipe window that produced run A -- consistent
with the standing candidate (SwiftShader's software rasterisation
loading the CPU during a gesture) but **not a confirmed cause**,
since both valid attempts succeeded despite the rise. Whether load
of that shape is what caused the *earlier* session's drops remains
unknown; this pass's sampler evidence neither confirms nor refutes
it, only shows the correlate is present under load without a
failure to correlate it to this time.
**Not attempted this pass**: the second `-gpu host` pair (time went
to the software-mode pair, the sampler, and diagnosing the dropout
above); a per-phase breakdown inside iris's own `FrameReport` the
way Compose's report has one; and syntax-highlighting/tappable-link/
accessibility-name gaps already named in "What remains" above,
unchanged.
**Verification for this update**: no Rust or Kotlin code changed
this pass (build/measurement only), so `cargo fmt`/`clippy`/`test`
were not re-run; `docs/DECISIONS.md`'s DEFERRED item is updated with
this table's headline numbers below rather than a decision made
here.
## For the next agent
What to do when you pick this up, in order, so nothing here has to be