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a894879d28
Captures medians of 5 runs for multitab and render-churn so tonight's
wins can't silently regress.
idle-cost is deliberately NOT gated. Its render attribution and idle
commit rate are trustworthy and are what the scenario exists for, but the
drag fps it reports (~0.6fps, p95 814ms) contradicts a direct
single-clock probe of the same gesture on the same build (57fps). I ruled
out sash selection, tile setup, render-counter residue, and a 20s soak,
and could not explain the gap — so the metric ships as a report, not a
gate. Gating CI on a number I can't defend would either fire on a phantom
or mask a real stall.
tier: 'report' is outside GATED ('ci','cold'), so the scenario still runs
and prints but neither compares nor writes a baseline.
91 lines
4.6 KiB
Markdown
91 lines
4.6 KiB
Markdown
# Desktop perf harness
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One systematized way to measure desktop rendering/interaction performance,
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diff it against a committed baseline, and fail on regressions. It replaces the
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dozen one-off `measure-*` / `profile-*` scripts that each reinvented the CDP
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client, arg parsing, stats, and output (and never had a baseline).
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## Quick start
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```bash
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# Isolated instance (recommended) — no running app or LLM credits needed.
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# Its own --user-data-dir + HERMES_HOME means it never collides with `hgui`.
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npm run perf -- --spawn
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# Or: launch an isolated instance once, attach repeatedly (faster iteration).
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npm run perf:serve # leaves an instance on :9222
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npm run perf # attaches, runs the CI suite, gates on baseline
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# One scenario, with a CPU profile:
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npm run perf -- stream --cpuprofile --tokens 800
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# Representative PRODUCTION numbers (minified React, not the ~3x-slower dev build):
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npm run perf -- cold-start stream keystroke transcript --spawn --prod
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# Re-capture the baseline on your reference device, then commit baseline.json:
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npm run perf -- cold-start stream keystroke transcript --spawn --prod --update-baseline
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```
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## Dev vs prod
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By default the harness measures the **dev** renderer (fast to spin up, good for
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relative regression checks). Pass `--prod` (with `--spawn`) to build a
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production renderer *with the probe included* (`VITE_PERF_PROBE=1`) and measure
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minified React — the representative shipped numbers. The committed baseline is
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captured with `--prod`.
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## Why isolation matters
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The measurement this harness exists to run was historically blocked: a running
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`hgui` holds the Electron single-instance lock, so a second instance quit
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immediately. `--spawn` / `perf:serve` launch with their own `--user-data-dir`
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(separate lock scope), their own `HERMES_HOME` (separate backend + sessions),
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and their own `--remote-debugging-port`. Synthetic scenarios drive `$messages`
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directly via `window.__PERF_DRIVE__`, so no LLM credits are spent.
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## Scenarios
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| scenario | tier | measures | replaces |
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| `stream` | ci | streaming longtasks, frame p95/p99, mutation cadence | measure-synthetic-stream, profile-synth-stream, profile-long-stream |
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| `stream --real` | backend | same, from a real LLM stream | measure-real-stream, profile-real-stream |
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| `keystroke` | ci | composer keystroke → paint latency | measure-latency, profile-typing, leak-typing |
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| `transcript` | ci | large-transcript mount + paint cost | (new) |
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| `render-churn` | ci | per-component render attribution + store churn while N tabs stream | (new) |
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| `idle-cost` | report | busy-but-silent tiles: idle commit rate, + fps while resizing / typing | (new) |
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| `cold-start` | cold | launch → CDP → driver → first paint (fresh spawn/run) | (new) |
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| `first-token` | backend | Enter → first assistant token painted (TTFT) | (new) |
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| `submit` | backend | Enter → cleared → user msg painted, scroll jump | measure-submit, measure-jump |
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| `session-switch` | backend | route → first-paint → settle | profile-session-switch |
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| `profile-switch` | backend | rail click → sidebar settled | measure-profile-switch |
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`ci` + `cold` scenarios need no backend/credits and are gated against
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`baseline.json` (`cold-start` requires `--spawn` since it measures a fresh
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launch, and must be run in its own invocation). `backend` scenarios need a live
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backend (and `--spawn` or a real session/credits) and are report-only.
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CPU profiling is a cross-cutting `--cpuprofile` flag on any scenario (it wraps
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the run in `Profiler.start/stop` and prints a top-self-time table), replacing
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every standalone `profile-*` script.
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## Adding a scenario
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Create `scenarios/<name>.mjs` exporting `{ name, tier, description, run(cdp, opts) }`
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where `run` returns `{ metrics, detail }` (metrics = flat numbers, lower is
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better), then register it in `scenarios/index.mjs`. If it's `ci`, add a
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`baseline.json` entry (or run `--update-baseline`).
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## Layout
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- `lib/cdp.mjs` — the one CDP client + target discovery + typing + CPU-profile wrapper + DOM selectors.
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- `lib/stats.mjs` — percentiles, histograms, CPU-profile self-time ranking.
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- `lib/baseline.mjs` — load/compare/update the baseline + regression gate.
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- `lib/launch.mjs` — attach, or spawn a fully isolated instance.
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- `scenarios/` — one module per measurement.
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- `run.mjs` — entrypoint. `serve.mjs` — standalone isolated launcher.
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## Not migrated (kept as dev utilities)
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`eval.mjs`, `reload.mjs`, `reload-renderer.mjs`, `probe-renderer.mjs`,
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`probe-thread.mjs`, `click-session.mjs`, `diag-*.mjs` are interactive dev
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helpers, not benchmarks. They can adopt `lib/cdp.mjs` in a follow-up.
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