[shinaoka]

Lessons from the faer fork's values-only SVD work of 2026-10-23 (perf/svd-dqds, worklogs 2026-10-23-blocked-bidiag.md and 2026-10-23-dqds-shift.md; campaign runs 20261023T1* in faer-benchmark).

rules/benchmark/measurement.md

• The agent is a process too: pin the agent's own process and other agents (taskset -apc, separate command, then start the recorder fresh); the toolkit's observer_audit --confine. The Claude Code process started with affinity 0-23 although its login shell was pinned; record_run.py refused on another agent (codex) once.
• No commit or edit in any measured repository while a run is in flight: the recorder compares HEAD and clean state between process sets; a worklog commit in the library checkout nearly ended a run (recovered by detaching HEAD at the recorded revision).
• Build the harness only through its build script: a plain cargo test re-resolved Cargo.lock to the registry crate, a filtered diff hid the version lines, and the next recording stopped at the patch guard — a two-hour restart.

rules/rust/performance.md

• A work copy's leading dimension must not be a multiple of 1 KiB (L1 set aliasing; bidiag 512 at 8T 18.6 -> 15.3 ms with 64 bytes of padding per column; every benchmark shape is a power of two).
• Rows of a column-major matrix are strided operands: gather once, work contiguous, scatter once.
• A caller with a thread budget holds a faer team (faer::team::with_team(width, |par| ...)) around its calls and passes par inside; the library does not create it (maintainer's decision, 2026-10-23); 25.5 -> 19.2 ms at 512, 8T.
• Inside the closure, other parallel work runs on the same team, not through a raw rayon iterator that competes with the held members.

🤖 Generated with Claude Code

[shinaoka]

Added rules/common/performance.md → Optimising Against Proprietary Software: the vendor is a yardstick, not a source. Allowed: public-API timing, public docs, hypotheses tested on our code, licence-compatible published algorithms with citation. Not allowed: disassembly/decompilation/tracing, profiler sampling into vendor internals, reading vendor source, carrying over constants learned from it, uncredited translation of a reference implementation. Provenance recorded in the worklog and ledger row. (maintainer's request, 2026-10-24)