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Claude
328aafae77
Commit the spec and scaffold the system it describes:
- SPEC.md: the full v0.1 engineering spec
- crates/: trust-layer Rust workspace, unit-tested
- bench-runner: interleaved ABAB scheduling with discarded warm-ups,
deterministic bootstrap CIs over the ratio of medians,
CI-lower-bound accept rule, env fingerprinting, and a CLI with
compare + A/A self-test modes (A/A verified passing end-to-end)
- diff-test: gate outcome model, sha256 corpus pin verifier that
refuses on mismatch, per-target equivalence policy parser
(byte-identical default, explicit fp-tolerance opt-in)
- ledger: append-only SQLite attempt schema with UPDATE/DELETE
refused by triggers, anti-double-attempt query
- report: cores-saved and dollars/yr ROI math over speedup CIs,
pricing.toml inputs
- playbook/: classes 1-7 with preconditions, procedure, verification
notes, and known failure modes per class
- agent/: Python package skeleton — six-tool contract and prompting
spine, harness IPC deferred to Phase 1
- config/: accept.toml (2% threshold, 30 runs/side), pricing.toml
- targets/, corpora/, results/calibration/: layout and policy docs
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2
1.8 KiB
1.8 KiB
Class 4 — Data layout
Make the memory hierarchy work for the access pattern.
Preconditions
- Profile signature: high cache-miss rate in
perf stat(LLC misses per instruction), hot loops whose flamegraph frames are memory-bound (perfcycles concentrated on loads), low IPC (<1) on wide cores. - For false sharing: multithreaded target where per-thread throughput
degrades as threads are added;
perf c2cconfirms.
Procedure (cheapest first)
- Struct field reordering / packing: kill padding, group hot fields on
one cache line, split hot/cold (
#[repr(C)]review, cold-field box-out). - AoS→SoA for loops that touch one field across many elements — restructure the container, not the algorithm.
- False-sharing fixes: pad or align per-thread state to 64 bytes
(
#[repr(align(64))],crossbeam_utils::CachePadded). - Cache blocking / loop tiling for nested loops over large matrices or images; tile to L1/L2, verified empirically, not by datasheet.
Verification notes
- Layout changes to any type that crosses FFI, serialization, or hashing
boundaries can change observable behavior (struct hash, serialized
bytes, memcmp-based equality) — golden replay catches this; check the
target for
#[repr]-sensitive traits before patching. - Differential fuzz the functions whose types changed, not just the functions whose code changed.
Known failure modes
- Reordering fields of a type that derives
Hash/Ordused in ordered iteration → output order changes → replay divergence (correct reject). - AoS→SoA wins the target loop but loses every other access site; the end-to-end number is the verdict, not the microbench.
- Alignment padding blowing up per-element size until the working set falls out of cache — the cure worse than the disease.