A zero-dependency perf-test harness for Rust and Java that records timed samples per stage, computes percentiles, supports coordinated-omission correction, and emits a stable JSON contract the rest of the ecosystem consumes.

repo	one-line	status
subms	The library. subms on crates.io; com.submillisecond:subms on Maven Central.

16 dual-language Rust + Java recipes, 3 Java guides, all writeups + perf JSON, and the discovery CLI - one repo, one clone, the whole working notebook. Every recipe ships >= 90% line coverage, a documented quality-bar contract (reference impl + claim conditions + non-claims), and an asserted sub-millisecond p99 in CI.

repo	one-line	status
subms-cookbook	Recipes (subms-bloom-filter, subms-lsm-tree, subms-hyperloglog, ...) + guides + content + @submillisecond/subms CLI.

The Next.js site that renders submillisecond.com - cookbook, blog, glossary, and topic pages. Statically exported to Cloudflare for prod; local dev runs an admin layer for editing posts + glossary entries straight to disk.

repo	one-line	status
subms-ui	Next.js 15 + React 19. Renders the cookbook content + perf JSON; deploys to Cloudflare Workers via ks publish subms-ui:ui.

Composable actions that diff perf JSON against a baseline, post a sticky PR comment with per-stage deltas, fail the status check on regression, push to 13 downstream sinks (Slack/Datadog/Prometheus/S3/...), and detect slow drift across a rolling window.

repo	one-line	status
subms-action-bench	Run a bench command, capture JSON, validate, retry on flake.
subms-action-diff	The gate. Baseline vs candidate -> sticky PR comment + status check.
subms-action-diff-aggregate	Roll N matrix diffs into one PR comment + one verdict.
subms-action-diff-sink	Push diff JSON to 13 sinks: Slack, HTTP, S3, GCS, Azure, Prometheus, InfluxDB, Datadog, Splunk, NewRelic, Honeycomb, file, stdout.
subms-action-drift	Detect slow drift (Welford rolling mean +/- k*sigma).
subms-actions	Umbrella - reusable workflow + pre-commit hook + shared scripts + suite docs.

• One JSON shape across runtimes. Rust + Java emit it natively (via the subms crate / jar); JMH, Criterion, HdrHistogram plug in via ~60-LOC adapters. One pipeline accepts them all.
• Status-check tollgate. The action fails the PR's check on regression - branch-protection rules can block merges automatically.
• Sticky PR comments. Re-runs and force-pushes update the same comment. No 32-comment matrix spam.
• Drift detection. Catches "p99 has been creeping +1 %/week for 8 weeks" that base-ref diffing misses.
• Enterprise-grade transport. HTTPS_PROXY / mTLS / custom CA bundles / retry-with-backoff / PII scrubbing.
• Zero npm install. Composite actions + Node std-lib only. Works on any GitHub runner without dependency setup.

Three-step CI gate for a Rust crate:

# .github/workflows/perf.yml
name: perf
on:
  pull_request:

permissions:
  contents: read
  pull-requests: write

jobs:
  diff:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with: { fetch-depth: 2 }

      - name: Snapshot baseline
        run: git show ${{ github.event.pull_request.base.sha }}:perf/myworkload.rust.json > baseline.json

      - name: Use PR perf JSON
        run: cp perf/myworkload.rust.json candidate.json

      - uses: submillisecond/subms-action-diff@v0
        with:
          baseline: baseline.json
          candidate: candidate.json
          threshold-pct: "15"

Or one call wraps bench -> diff -> sink -> drift via the reusable workflow.

The submillisecond.com cookbook is a working notebook of low-latency engineering. 16 dual-language Rust + Java recipes that hit sub-millisecond at p99 - bloom / cuckoo / HLL / count-min / HDR-histogram / SPSC / MPSC / rate-limiter / timer-wheel / arena / ART / treap / LSM / segment-reader / merge-iterator / block-cache. Each comes with a quality bar contract, >= 90 % test coverage, and real measured bench numbers from the subms perf harness.

Pre-release. The actions are functionally complete, smoke-tested via their own self-test workflows, and ready for use. They have not yet been through real-world adoption beyond the cookbook itself. Bug reports welcome.

Releases follow semver. Float to a major tag (@v0) for auto-patches; pin to an exact tag (@v0.1.0) for supply-chain audit.

• Web: submillisecond.com
• Terms: submillisecond.com/terms
• Security: see each repo's SECURITY.md for private vulnerability reporting.

_{Released under the MIT License. The submillisecond name and logo are not registered trademarks; use in editorial and reference contexts is encouraged, use in product names that imply endorsement is not.}