Perf regression: maven/hosted cpu +23% (9c43dfc9..17793173) #1472

[agent] Bench: maven/hosted and maven/rescan now use about 21–23% more CPU, about +18 ms and +16 ms per scan. Wall time is flat or better because the extra work runs in parallel. This is the second consecutive run at 10% or more (10-12: maven/rescan CPU +22.1% day, maven/hosted CPU +30.8% week).

(RSS differed between the two rounds, +0% and +23–28%, so treat the RSS figure as unconfirmed.)

• Base: 9c43dfc9 (2026-10-06). Head: 15c2c839 (2026-10-13). The daily A/B (17793173 → head) is flat.
• Range: one bisect point, f3c6313a, shows about half the CPU increase (+11.5%). The rest lands in f3c6313a..17793173, where the candidates are Fix project-mode Maven crawl listing all of ~/.m2 (#265) #1361 (project-mode Maven crawl), Fix hosted Maven reactor silently unpatched (#261) #1349 (hosted Maven reactor), Fix hosted Maven pom edits outside live markup (#259, #262, #342) #1327 and Fix vendored Maven pin overriding BOM/parent management (#488) #1359. The first half's candidate is Route JVM layout through one module and fix three JVM scope bugs #1032 (JVM layout routing).
• Hot spot (callgrind, head, maven/hosted): MavenCrawler::crawl_all_with per-artifact closure takes 47% of Ir. Inside it, crawlers::maven_scope::project_scope takes 36%, through maven_scope::read_model → vendor::jvm::maven_reactor::pom_model / Doc::parse (19%) and formats::xml::elements (13%). The project's pom model looks like it is re-read and re-parsed per crawled artifact rather than once per scan.

Repro:

export CARGO_PROFILE_PERF_INHERITS=release CARGO_PROFILE_PERF_LTO=thin CARGO_PROFILE_PERF_STRIP=none
git worktree add /tmp/base 9c43dfc9 && (cd /tmp/base && CARGO_TARGET_DIR=/tmp/tb cargo build --locked --profile perf -p socket-patch-cli)
cargo build --locked --profile perf -p socket-patch-cli -p socket-patch-bench
target/perf/socket-patch-bench compare --base /tmp/tb/perf/socket-patch --head target/perf/socket-patch -f '^maven/' --runs 20

Runner: 4 vCPU, Intel(R) Xeon(R) Processor @ 2.10GHz (cloud sandbox), run 2026-10-13.

Generated by Claude Code