Harry Bayliss
b05065a601
Removed low/marginal items from the original sweep; remaining items have measured or workflow evidence to justify action.
116 lines
6.2 KiB
Markdown
116 lines
6.2 KiB
Markdown
# Perf Audit (reviewed 2026-05-15)
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Findings that survived the 2026-05-15 review pass. Low and marginal
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items from the original sweep were removed; remaining items have enough
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measured or workflow evidence to justify action.
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Baseline benchmark numbers (`go test -bench=. ./internal/app/`, AMD
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Ryzen 7 7800X3D, libghostty-vt **ReleaseFast** after the Makefile
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fix landed):
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```
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# Renderer alone
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ViewportRenderer_PlainASCII 229 MB/s 1.3 KB/op 6 allocs/op
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ViewportRenderer_StyledLines 89 MB/s 91 KB/op 4325 allocs/op
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ViewportRenderer_RatatuiBurst 40 MB/s 365 KB/op 17306 allocs/op
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RendererThroughput_ReuseInstance 90 MB/s 316 KB/op 17380 allocs/op
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ContainsOSC_NoOSC 3050 MB/s 0 B/op 0 allocs/op
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# ASCII-video stream (renderer only — 3 sec at the target fps)
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ASCIIVideo_Stream_8Color_120fps 260 µs/frame 3845 fps_ceiling 3.1% budget
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ASCIIVideo_Stream_TrueColor_120fps 576 µs/frame 1735 fps_ceiling 6.9% budget
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# Full pipeline (em.Write + renderer + io.Discard write)
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Pipeline_ASCIIVideo_8Color_120fps 493 µs/frame 2030 fps_ceiling 5.9% budget
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Pipeline_ASCIIVideo_TrueColor_120fps 1075 µs/frame 931 fps_ceiling 12.9% budget
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# Emulator alone (libghostty-vt CSI/SGR parser)
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Emulator_Write_Stream_8Color_120fps 257 µs/frame 3890 fps_ceiling
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Emulator_Write_Stream_TrueColor_120fps 488 µs/frame 2051 fps_ceiling
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```
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The current pipeline still has large 120 fps headroom. The remaining
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renderer concern is multi-MiB styled replay latency and allocation
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churn, not normal steady-state frame budget.
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- [ ] **viewport renderer allocates heavily on SGR/CSI-heavy chunks.** [MEDIUM]
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- Review evidence: five benchmark reps confirmed
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`ViewportRenderer_StyledLines` at about 4,325 allocs per 16 KiB
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chunk (~91.5 KB/op, roughly 1 alloc per 3.8 input bytes), and
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`ViewportRenderer_RatatuiBurst` at about 17,306 allocs per chunk
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(~365 KB/op). A 5 MiB styled resume benchmark allocated about
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31 MB across 1.38M objects.
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- Likely hot paths: generic CSI/SGR output in
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`internal/app/viewport_renderer.go` sends many sequences through
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`vr.shifter.Shift(vr.buf)`, while `internal/app/cursorshift.go`
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returns a fresh `[]byte` via `pending.String()` on every
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`Shift` call and parses CSI params through `string(raw)` /
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`strings.Split`. The mode-helper `string(params)` conversions
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are real, but probably not the main SGR-heavy cost.
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- Fix direction: make `cursorShifter` write into caller-owned
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scratch output or directly into the viewport renderer's pending
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builder; parse CSI params from byte slices; pre-grow/reuse
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renderer and shifter buffers. Re-run styled-lines, ratatui, and
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5 MiB resume benchmarks; use pprof when available to confirm the
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top allocation sites.
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- [ ] **large styled resume/replay dumps spend visible time in viewport rendering.** [MEDIUM]
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- Review evidence: `BenchmarkSessionResume_5MiBStyled` measured
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about 58 ms median and 63 ms p95 over five reps. The plain 5 MiB
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benchmark was about 23-24 ms with only 21 allocs. The live path
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renders focused PTY chunks through `renderer.Render`, then still
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pays emulator writes, ring writes, event dispatch, stdout writes,
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and real terminal paint.
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- Scope: this is not a Codex steady-state throughput limit. A
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100 KB/s stream is far below the styled renderer's ~80-90 MB/s
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ceiling. It matters for multi-MiB burst replay, resume/startup
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dumps, and dense full-screen churn.
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- Fix direction: do the allocation fix first, since it should also
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improve throughput. After that, invest further only if styled
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resume traces remain user-visible or the styled-lines benchmark
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is still under roughly 300 MB/s.
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- [ ] **wait_for_pattern re-scans the entire stream/grid while waiting.** [MEDIUM]
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- `internal/app/host.go:476-493` (the `check` closure). On
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`scope="scrollback"` it calls `c.StreamRead(0)` followed by
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`stripANSIBytes(nil, b)`, so each check can copy, strip, and
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search the full 1 MiB ring. On `scope="grid"` it calls
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`PlainText()` and runs the regex against the full grid string.
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- Caveat from review: the current chunk notifier coalesces bursts
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with a buffered channel and has a 500 ms fallback, so this is not
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necessarily one full scan per PTY chunk. It is still meaningful
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for active waits on chatty panes.
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- Fix direction: for `scrollback`, track the last checked stream
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offset and search only new output plus a bounded overlap/scratch
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buffer so matches spanning chunks are not missed. For `grid`,
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dedupe on `ScreenVersion()` and skip work when the version has
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not changed.
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- [ ] **search_output rebuilds and searches whole scrollback on every call.** [MEDIUM]
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- `internal/app/host.go:428-437` compiles a fresh regex, reads the
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stream from offset 0, strips ANSI for `kind="rendered"`, converts
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the full buffer to a string, and splits it into lines before
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applying `limit`. This is meaningful when agents poll the same
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pattern; it is low impact for ad hoc searches.
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- Fix direction: cache compiled regexes by pattern; cache stripped
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rendered output by child id and stream end offset; avoid
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`strings.Split` over the whole ring when only the first `limit`
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matches are needed. Prefer an incremental search shape if this
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becomes the standard "watch for marker" path.
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# On Hold
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- [ ] There's a unicode <?> being displayed in opencode [ON HOLD]
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- Investigated 2026-05-14: patterm passes ghostty grapheme codepoints
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through unchanged (vt/ghostty.go:452-462), so the `<?>` glyph is
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most likely the *host* terminal's font fallback for opencode's
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Nerd Font private-use codepoints, not a patterm substitution.
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Need a concrete reproduction (which codepoint, which host
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terminal/font) before changing rendering.
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- [ ] After codex rips for like 15 minutes, the terminal becomes quite slow. [ON HOLD / VERIFYING]
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- 2026-05-14: Perf plan P1-P11 landed (see CHANGELOG). Needs a real
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long-running codex session to confirm whether the steady-state
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slowdown is gone or some hotspot remains. Capture a pprof if it
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still feels slow after ≥15 minutes — the structural drivers the
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audit named are all addressed, so a remaining symptom is a new
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one and probably wants fresh profiling.
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