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