food_chain/docs/performance-cost-audit

Performance / Memory Cost Audit

Purpose

Audit the integrated Mandelbrot viewer for processing that is low-value, redundant, or harmful from a speed / memory perspective. This audit intentionally does not remove or alter any production behavior in index.html.

Production source audited:

• index.html
• SHA-256: 544820c5024cf6d56e012db6d1bec3ddfcef5d833691b890baa64b26c5c2ee5a
• Regression: PASS, 19 WGSL kernels

Measurements are CPU/static surrogates unless explicitly stated. Real WebGPU frame timing is not available in this container because the browser WebGPU backend cannot initialize successfully here.

Conclusions

A — High-confidence waste / harmful cost

ID	Finding	Cost	Benefit observed	Confidence
A1	Numeric history is recopied after every accepted recolor	8 B/px copy per recolor	Numeric data did not change	Very high
A2	cpuFrameRgba retains the assembled CPU fallback frame but is never read	4 B/px JS heap retained	None	Very high
A3	certifyInterior() runs a full-frame unknown-statistics pass and waits for GPU completion before primary compute	Full meta scan + queue synchronization	Partial proof/history-seed caller does not consume these stats	Very high
A4	Strict direct rendering still updates Brent-cycle state even though periodicity classification is disabled	Per-iteration ALU/register state	None in strict mode	Very high
A5	Export workspace survives export completion	Up to ~24 MiB GPU memory with 512 tiles / 3 slots	None while not exporting	Very high
A6	Deep active/correction workspaces survive the hard frame that required them	active workspace up to ~44.1 MiB standard / ~176.5 MiB high; dense correction queue 4/16 MiB	None on later easy frames until reuse/resize	High

B — Strong optimization candidates, but keep until GPU A/B validation

ID	Finding	Evidence	Assessment
B1	Numeric history is always resident although exact-grid pan reuse is restrictive	8 B/px resident. Under common budget-scaled resolutions, integer CSS pans 1–100 px produced 0/100 exact-grid reuse hits in the static alignment test	Likely over-allocated; make lazy/telemetry-driven rather than delete immediately
B2	CPU exact cardioid/bulb tile proof runs for every numerical frame	1024×768: ~4.8–6.1 ms median; 2048²: ~25–28 ms median. Four of six fixed corpus views certified 0 pixels	Add cheap spatial gate; direct backend especially needs A/B comparison
B3	fast-coverage-repair runs a full-screen FAST pass after tiled coverage	Tile loops cover the full compute domain; mode 2 only repairs reason=0 untouched metadata	Likely redundant defensive pass; instrument reason=0 count before removal
B4	captureColorSource() snapshots meta+smooth during rendering	8 B/px copy per snapshot; provisional snapshots can occur every 125 ms. Snapshot allocation is 12 B/px	Useful only for live recoloring while render is in flight; gate more aggressively
B5	Color-auto idle mode retains a color snapshot	standard ~12 MiB, high ~48 MiB at preset caps	Idle color-auto recolor path uses current field, not recolorPublished()
B6	Adaptive initial-iteration probe uses high-precision scoring before every adaptive frame	Fixed corpus: ~1.3–12.5 ms and all six chose 350. Exploratory views can choose 512, so feature is not useless	Cache/gate/replace with cheaper trigger; do not delete blindly
B7	Active continuation can replay already-performed iterations	initial OP_LIMIT session starts state at n=0; reference change resets progress to 0; recovered pixels can rebuild whole active session	Potentially large on the hardest views; add replay counters before redesign

C — Expensive but currently justified / not a deletion target

• General periodicity detection: CPU surrogate showed ~98% iteration reduction in period-3 interiors. It can add overhead on boundary-only views, but removal is not justified.
• Sparse numerical correction and reason bucketing: it adds full scans/queue construction, but isolates expensive DS/BigInt work. Needs GPU A/B before structural change.
• Stable texture reprojection: consumes one history texture but directly improves interaction latency.
• Reference cache / guided multi-reference: memory cost is bounded and prior evaluation showed reduced perturbation mismatch.
• Series approximation: small reference metadata cost with large deep-zoom iteration skip in prior evaluation.

Key measurements

Recolor numeric-history copy bandwidth

commitHistory() always calls commitNumericHistory(). Therefore a color-only update copies unchanged meta and smooth buffers (8 B/px). Color auto can request a pass every 50 ms while idle.

preset cap	unchanged numeric copy / recolor	at 20 Hz
fast, 524,288 px	4 MiB	80 MiB/s
standard, 1,048,576 px	8 MiB	160 MiB/s
high, 4,194,304 px	32 MiB	640 MiB/s

This is in addition to the actual color pass bandwidth.

Color snapshot

captureColorSource() allocates/copies:

• meta: 4 B/px
• smooth: 4 B/px
• texture: 4 B/px

Resident cost = 12 B/px: ~6 MiB fast, 12 MiB standard, 48 MiB high at preset caps. A provisional snapshot copies 8 B/px and can be refreshed at up to 8 Hz, equivalent to ~32 / 64 / 256 MiB/s at the preset caps.

Exact interior tile proof

Seven-run median on this host:

view	1024×768	certified	2048×2048	certified
overview	~6.1 ms	7.3%	~25.5 ms	8.6%
period3 bulb	~5.1 ms	0%	~26.5 ms	0%
period3 core	~4.8 ms	0%	~28.1 ms	0%
seahorse boundary	~6.0 ms	0%	~25.1 ms	0%
seahorse deep	~5.6 ms	0%	~26.1 ms	0%

The exact proof is still useful in views that overlap the main cardioid / period-2 bulb, especially on the perturbation path. The issue is unconditional invocation, not the proof mechanism itself.

Exact-grid numeric-history reuse

The history seed requires identical span and an approximately integer render-pixel shift. When the resolution is pixel-budget limited, render pixels often do not align with CSS pixels.

Examples from the current resize rule, testing integer CSS horizontal pans of 1–100 px:

screen / quality	render size	reuse hits
1920×1080 / fast	965×543	0/100
1920×1080 / standard	1365×768	0/100
1920×1080 / high	2731×1536	0/100
1024×768@1× / standard	1024×768	100/100

This is a static alignment test, not real interaction telemetry. It supports making numeric history conditional rather than proving that it has no value.

Persistent workspaces

• Sparse active workspace, worst full-active capacity: ~44.1 MiB standard, ~176.5 MiB high.
• At 10% active: ~5.64 MiB standard, ~22.51 MiB high.
• Dense deep correction queue: 4 MiB standard, 16 MiB high.
• Export workspace at 512 tile, depth 3: ~24 MiB retained after export.
• Non-AA export currently allocates four 512² sample textures, ~4 MiB per slot, although 1× rendering does not need the four AA sample textures.

Static code locations

• index.html:1299-1300: pre-primary unknown stats + synchronization in certifyInterior().
• index.html:1383-1384: full numeric-history copy.
• index.html:1416: commitHistory() always commits numeric history.
• index.html:1822: color-only recolor promotes history and therefore triggers numeric copy.
• index.html:1718: state.cpuFrameRgba=rgba; the state value has no reader.
• index.html:162-163: cycle state still updated in strict direct mode.
• index.html:1349-1350: tiled FAST coverage followed by full-screen coverage-repair pass.
• index.html:1751-1756: provisional color snapshots at 125 ms throttle.
• index.html:1774: old completed field snapshot at every numerical render start.
• index.html:1866: idle color-auto snapshot allocation.
• index.html:1218: active workspace persists unless another active allocation request causes a >4× shrink.
• index.html:1217: full-pixel dense correction queue persists once allocated.
• index.html:1222-1226, 1898-1944: export workspace lifetime extends beyond export job.
• index.html:1306-1307, 1648, 1654: active continuation reinitialization/rebuild can reset progress.

Recommended instrumentation before deleting anything

1. Add counters for numeric-history attempt / hit / reused pixels / bytes copied.
2. Count reason-0 pixels immediately before fast-coverage-repair; if consistently zero, remove/disable that pass in an A/B branch.
3. Record certifiedInteriorTiles CPU ms and certified ratio per frame; gate when hit rate stays zero.
4. Record active-continuation reinitCount and replayedPixelIterations.
5. Record peak/resident bytes for active, correction, export, color snapshot and release-on-idle experiments.
6. Separate color-history promotion from numeric-history promotion and A/B color-auto frame time.

Production integrity

No production deletion or behavioral modification was made by this audit. Regression was rerun after inspection and passed.