performance.yml

name: Performance

# Instruction-count regression measurement.
#
# Deliberately NOT wall-clock: a shared GitHub runner's elapsed time moves more
# between runs than most real regressions, so a wall-clock threshold is either
# too loose to catch anything or too tight to trust. Callgrind counts executed
# instructions under emulation, which is independent of machine load and
# reproducible run-to-run, so a change in it is a change in work done.

on:
  # Prose and the docs site execute no measured code.
  pull_request:
    paths-ignore:
      - "docs/**"
      - "**/*.md"
  push:
    branches: [main]
    paths-ignore:
      - "docs/**"
      - "**/*.md"
  workflow_dispatch:

permissions:
  contents: read

concurrency:
  group: performance-${{ github.ref }}
  cancel-in-progress: true

jobs:
  regression:
    name: Instruction-count regression
    runs-on: ubuntu-latest
    timeout-minutes: 45
    steps:
      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
        with:
          # The comparison needs the base commit to measure against.
          fetch-depth: 0

      - uses: dtolnay/rust-toolchain@7e38f4b43b4db5c8dd498af069a4f6196df1d067
        with:
          toolchain: 1.99.1

      - name: Install valgrind
        run: |
          sudo apt-get update
          sudo apt-get install -y valgrind

      - name: Read the declared iai-callgrind version
        id: iai
        run: |
          version="$(grep -m1 '^iai-callgrind' tools/benchmark/Cargo.toml | sed 's/.*"\(.*\)".*/\1/')"
          echo "version=${version}" >> "$GITHUB_OUTPUT"

      # The runner binary must match the library version exactly or it refuses
      # to run, so the version is read from the manifest rather than pinned
      # twice and allowed to drift.
      - name: Install iai-callgrind-runner
        run: cargo install iai-callgrind-runner --version "${{ steps.iai.outputs.version }}"

      - name: Measure the base commit
        if: github.event_name == 'pull_request'
        run: |
          git checkout --quiet "${{ github.event.pull_request.base.sha }}"
          # A base commit predating the benchmark crate has nothing to measure;
          # that is not a failure, it is the first run.
          if [ -d tools/benchmark ]; then
            bash scripts/bench-regression.sh || true
          else
            echo "base commit has no benchmark crate; nothing to compare against"
          fi
          git checkout --quiet -

      - name: Measure this commit
        run: bash scripts/bench-regression.sh

      - name: Keep the measurements
        if: always()
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: callgrind-measurements
          # Honour a CARGO_TARGET_DIR override if one is ever set.
          path: ${{ env.CARGO_TARGET_DIR || 'target' }}/iai/
          if-no-files-found: ignore
          retention-days: 14