148 lines
6.5 KiB
Markdown
148 lines
6.5 KiB
Markdown
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# Runtime cost removal pass
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Date: 2026-09-29
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## Purpose
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This build applies every removal/reduction that the preceding A/B pass supported strongly enough to change without redesigning numerical state. The original integrated build remains separately available at `/mnt/data/mandelbrot_integrated`; this directory is the experimental production-equivalent removal build.
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Production source of truth in this build: `index.html`.
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## Applied changes
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### 1. Recolor no longer copies numeric history
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Color-only recolor now promotes only color history. `meta/smooth` numeric history is not recopied when the numerical field did not change.
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A/B traffic avoided per accepted recolor at the preset caps:
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- fast: 4 MiB
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- standard: 8 MiB
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- high: 32 MiB
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At 20 Hz color cycling this removes 80 / 160 / 640 MiB/s of avoidable copy traffic respectively. These are byte counts, not measured GPU frame-time gains.
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### 2. Removed unread CPU fallback RGBA retention
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The CPU fallback still creates the RGBA array needed for `ImageData`, but no longer stores a second long-lived reference in `state.cpuFrameRgba`. The state property itself was removed.
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Avoided retained JS memory at the pixel caps:
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- fast: 2 MiB
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- standard: 4 MiB
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- high: 16 MiB
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### 3. Removed partial exact-interior pre-primary unknown scan
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`certifyInterior()` no longer runs a full-frame unknown-stat pass immediately before the primary numerical pass. The primary path computes the required statistics later. A fully certified frame now uses known-zero stats directly instead of a readback.
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Minimum avoided `fieldMeta` read per partial certification:
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- fast: 2 MiB
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- standard: 4 MiB
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- high: 16 MiB
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### 4. Removed FAST coverage-repair pass and its dead remnants
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The second full-screen FAST numerical pass that attempted to repair `reason=0` holes was removed. Validation before removal found zero holes in 36 layout cases plus 200 randomized semantic cases.
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After integration, two dead remnants were also removed:
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- the post-tile `numericParams` upload whose only purpose was coverage-repair mode 2;
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- the coverage-hole mode-2 branch in `FAST_PERTURB_WGSL`.
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Representative eliminated shader invocations:
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- 1365×768: 1,050,624 invocations
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- 2731×1536: 4,202,496 invocations
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The FAST kernel hash changed only because this unreachable coverage-repair branch was deleted. `tests/kernel_hashes.json` was updated accordingly.
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### 5. Removed idle color-auto snapshot allocation
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Turning on automatic hue cycling while no render is running no longer captures `colorSource`. Idle recolor does not consume that snapshot. Render-time snapshot behavior remains because it is used to keep visual continuity while a new numerical frame is in flight.
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Avoided idle snapshot residency at caps:
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- fast: 6 MiB
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- standard: 12 MiB
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- high: 48 MiB
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### 6. Export workspace is released after every export
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`runExport()` now destroys the reusable export ring in `finally`. This removes roughly 24 MiB of post-export residency in the tested 512×512 / depth-3 configuration. The next export must allocate the ring again; real-device allocation latency was not measurable in this environment.
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### 7. Exact-interior proof is spatially gated
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Before the BigInt tile proof, the exact viewport is tested against conservative bounding boxes for the main cardioid and period-2 bulb. If neither can intersect the viewport, the proof is skipped.
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A/B aggregate CPU proof time on the fixed corpus:
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- 1024×768: 41.64 ms → 25.16 ms (~39.6% reduction)
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- 2048²: 177.70 ms → 117.08 ms (~34.1% reduction)
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Random validation: 240 views, 160 gate-negative, 0 false negatives versus the existing exact tile proof.
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### 8. Numeric history is no longer permanently resident when exact-grid reuse is unrealistic
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`historyMeta/historySmooth` are allocated only when the render-to-CSS scale ratio has a reduced denominator ≤ 8. Native-grid cases retain the feature; common pixel-budget-scaled cases do not keep 8 B/pixel of history that almost never matches integer-grid pan reuse.
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Measured deterministic pan survey:
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- 1920×1080 → 965×543: 0.2% reuse, history removed (~4 MiB)
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- 1920×1080 → 1365×768: 0.6% reuse, history removed (~8 MiB)
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- 1920×1080 → 2731×1536: 0% reuse, history removed (~32 MiB)
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- 1024×768 native: 100% reuse, history retained
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- 1024×768 DPR2/native ratio: 100% reuse, history retained
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This is intentionally conditional rather than blanket deletion.
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### 9. Export AA sample textures are lazy
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The four RGBA8 sample textures used only by 2× AA export are no longer allocated by 1× export. At 512² and ring depth 3, 1× export avoids 12 MiB of peak sample-texture allocation.
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## Deliberately not removed
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The following were investigated but are not part of this deletion pass:
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- **Adaptive initial-iteration probe**: 3/48 survey views selected more than 350 iterations; forcing 350 increased the surrogate work metric by +7.2%, +25.3%, and +33.1%.
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- **Strict periodicity-state updates**: the CPU A/B did not establish a speed win; median B was slower.
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- **Continuation restart from n=0**: confirmed redundant work, but fixing it requires carrying valid continuation state across primary/reference transitions rather than deleting code.
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- **Deep/correction workspace lifetime**: potentially large memory saving, but unconditional release can cause GPU allocation churn; no real WebGPU allocation timing was available, so it remains unchanged in this pass.
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## Validation
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Commands:
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```bash
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node tests/regression.mjs
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node experiments/ab/variant_check.mjs index.html
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node experiments/ab/supplement.mjs
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node experiments/integrated_bench.mjs docs/removal-pass/integrated-bench.json
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```
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Results:
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- regression: PASS
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- JavaScript syntax: PASS
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- WGSL kernels: 19 + bundle version
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- exact-interior gate randomized test: 0 false negatives / 240 views
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- FAST coverage semantic test: 0 hole cases / 200 randomized cases
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- integrated CPU benchmark: completed; existing periodicity/series/sparse/multi-reference/CPU-fallback paths remain operational
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Real WebGPU frame-time p50/p95 remains unmeasured because the container cannot start a usable WebGPU adapter.
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## Source-size impact
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Compared with the preceding integrated build:
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- `index.html`: 223,672 → 224,559 bytes (+887 bytes)
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- gzip-9: 57,375 → 57,744 bytes (+369 bytes)
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The file is slightly larger because the spatial and allocation eligibility gates add code. The intended gains are runtime computation, transfer traffic, and memory residency rather than download size.
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## Integrity
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Removal-build `index.html` SHA-256:
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`e69b91ead027927d977a065d27d9e27629110122df20aa470eab877e23f77ac7`
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