hermes-agent/apps/desktop/scripts/diag-switch-autopsy.mjs
Brooklyn Nicholson 81779fa6a0 perf(desktop): don't backfill the transcript while its thread streams
Switching to a STREAMING session took ~1.4s to settle while an idle
session settled in ~50ms. The autopsy probe named it: the
FIRST_PAINT_BUDGET -> RENDER_BUDGET backfill runs as a transition, an
interrupted transition restarts from scratch, and stream flushes land
every 33-250ms — so the 300-part backfill re-rendered over and over
(measured: 1374ms settle, 30 commits, Primitive.div x2237 for one switch).

Gate the backfill on the thread being idle. The user lands on the live
tail immediately either way; older turns backfill the moment the run
ends, and 'Show earlier' remains the manual path meanwhile.

Measured on the live app (diag-switch-autopsy, real sessions):
  switch to idle session        ~35-55ms settled (unchanged)
  switch to streaming session   1374ms -> backfill deferred; lands at
                                the live tail like any other switch

Adds diag-switch-autopsy.mjs (per-switch settle/commits/top-renders) and
live-drive.mjs (status/fps/drag one-liners against the running app).
2026-07-27 01:14:29 -05:00

52 lines
1.8 KiB
JavaScript

// Session-switch autopsy: click between the two heaviest rows repeatedly,
// recording per-switch (a) settled ms, (b) React commits, (c) top rendered
// components — so slow switches name themselves.
import { attach } from './perf/lib/launch.mjs'
import { sleep } from './perf/lib/cdp.mjs'
const arg = (name, fallback) => {
const i = process.argv.indexOf(`--${name}`)
return i === -1 ? fallback : process.argv[i + 1]
}
const port = Number(arg('port', 9222))
const ROUNDS = Number(arg('rounds', 8))
const { cdp, teardown } = await attach({ port })
const SWITCH_ONE = index => `
(async () => {
const rows = [...document.querySelectorAll('[data-slot="row-button"]')].filter(el => el.offsetParent)
if (rows.length < 2) return JSON.stringify({ error: 'rows' })
const row = rows[${index} % 2]
const rc = window.__RENDER_COUNTS__
rc.start()
const t0 = performance.now()
row.click()
let lastMutation = performance.now()
const mo = new MutationObserver(() => { lastMutation = performance.now() })
mo.observe(document.body, { childList: true, subtree: true, characterData: true })
const deadline = performance.now() + 4000
while (performance.now() < deadline) {
await new Promise(r => requestAnimationFrame(r))
if (performance.now() - lastMutation > 150) break
}
mo.disconnect()
rc.stop()
const settled = Math.round(performance.now() - t0 - 150)
const report = rc.report(6).map(r => r.name + ':' + r.renders + '(' + Math.round(r.totalMs) + 'ms)')
return JSON.stringify({ label: (row.textContent ?? '').slice(0, 24), settled, commits: rc.commits(), top: report })
})()
`
try {
await cdp.send('Runtime.enable')
for (let i = 0; i < ROUNDS; i++) {
console.log(await cdp.eval(SWITCH_ONE(i)))
await sleep(400)
}
} finally {
teardown?.()
}