83352c4571
Replace the physical ekp-region renderer with ekp-buffer text-property projection backed by shared semantic layout plans and stable live-edit transactions. Optimize the C-backed resize hot path, and add deterministic performance, ERT, GUI, fuzz, release, and documentation coverage for task017 through task032. BREAKING CHANGE: require ekp-buffer instead of ekp-region and rename module-owned ekp-region-* settings to ekp-buffer-*.
54 lines
2.3 KiB
Markdown
54 lines
2.3 KiB
Markdown
# C Resize Hot-Path Ownership
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## Context
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The reported 60–70 ms resize number was initially described as C dynamic
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module performance. The measured operation actually crossed core planning,
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the Emacs module boundary, projection construction, text-property
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publication, and live-prefix replacement.
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## What the profile showed
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The portable C call averaged roughly 1.8 ms in the frozen four-round
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baseline. Repeated paragraph lookup and plan construction dominated the core
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path, while redundant gap measurement and property publication dominated
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the buffer projection path. Resize also published the active paragraph
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statically before replacing it with the live prefix.
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An apparent remaining 60–70 ms GUI spike was a separate phenomenon:
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`set-window-margins` allocated in the Emacs window system and a later EKP
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callback paid the resulting GC pause. The EKP mutator stayed below the
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50 ms contract when total, GC, and mutator time were recorded separately.
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## Decision
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Keep the C ABI and Knuth-Plass algorithm unchanged. Move prepared paragraph,
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DP, and natural gap geometry through the existing core-to-buffer path,
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remove only true no-op projection records, consolidate owned property
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publication, and make resize publish the active paragraph only through its
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live owner.
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## Rejected alternatives
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- Micro-optimizing C DP: it was not the dominant measured layer.
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- Increasing resize debounce or skipping widths: this hides work and makes
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projection stale.
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- Reusing approximate plans across widths: this breaks exact layout parity.
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- Raising the global GC threshold: this changes process-wide behavior and
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misattributes window-system allocation to EKP.
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## Consequences
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The four-round gate reduces core p95 from 42.006 ms to 27.687 ms and complete
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resize p95 from 46.611 ms to 27.487 ms, with 34.09% and 41.03% improvements.
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Frozen C, candidate C, and Elisp layout hashes remain identical. External GC
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can still increase wall-clock totals, but it is explicitly observable and
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is not concealed by runtime policy changes.
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## Verification and rollback
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The evaluator, normal/permuted/isolated ERT suites, fuzzing, warning-as-error
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builds, static and release gates, and reviewed temporal GUI evidence pass.
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Rollback is a direct revert of the prepared-data and publication changes;
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no compatibility layer or data migration is required.
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