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pcbjam/docs/ccache-benchmark.md
Viktor Vaczi 5b919ef66f Add ccache and incremental build system for faster development 
- Add ccache to Docker image for compiled object caching
- Change build defaults: incremental by default, skip deps by default
- Add new flags: --full, --clean-kicad, --build-deps
- Skip wxWidgets configure if already configured (check Makefile timestamps)
- Remove unused source hash stamp functions (make handles dependencies)
- Update build.md with new build system documentation

Performance improvements:
- Single file change: 7:35 → 1:34 (4.8x faster)
- No-change rebuild: 7:35 → 1:31 (5x faster)
- Asyncify post-processing (~1 min) is now the bottleneck

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
2025-12-26 20:51:58 +01:00

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ccache Build Performance Benchmark

Testing build times before and after adding ccache to measure the impact.

Test Environment

  • Machine: Apple Silicon (M4 Max)
  • Docker resources: 10 CPUs, 32GB RAM
  • Build command: ./docker/build.sh (defaults to incremental build)

Results

Step 1: Baseline (before ccache)

Command: ./docker/build.sh --skip-deps (forces KiCad rebuild, old default) Time: 7:34.93 (7 min 35 sec)

Step 2: First build with ccache (populating cache)

Command: ./docker/build.sh --skip-deps (old default) Time: 9:35.52 (9 min 35 sec) Note: Slower than baseline due to ccache overhead when populating cache Cache stats: 1335 misses, 0 hits, 1.39GB cached

Step 3: Single KiCad file change (incremental build)

Changed: kicad/pcbnew/board.cpp (added one line) Command: ./docker/build.sh (new incremental default) Time: 1:45.97 (1 min 46 sec)

  • Only board.cpp recompiled
  • Rest of compilation: instant (CMake detected no changes)
  • Most time spent on post-processing (asyncify ~1 min)
  • ccache hit rate: 25% (some preprocessed source matched)

Step 4: wxWidgets incremental build baseline (configure ran)

Command: ./docker/build.sh (after implementing skip-configure logic) Time: 7:43.87 (7 min 44 sec)

  • First build after script changes, so configure ran
  • This populates the wxWidgets build state for incremental builds

Step 5: No-change rebuild (configure skipped)

Command: ./docker/build.sh (no changes to any source files) Time: 1:31.13 (1 min 31 sec)

  • wxWidgets configure skipped (Makefile exists, configure.in unchanged)
  • wxWidgets make: instant (nothing to rebuild)
  • KiCad CMake/make: instant (nothing changed)
  • All time spent on post-processing (asyncify ~1 min)

Step 6: Single wxWidgets file change (incremental build)

Changed: wxwidgets/src/common/memory.cpp (added one line) Command: ./docker/build.sh Time: 1:33.99 (1 min 34 sec)

  • wxWidgets configure skipped
  • Only memory.cpp recompiled, library re-archived
  • KiCad links against updated wxWidgets
  • Most time spent on post-processing (asyncify ~1 min)

Summary

Scenario Before After Speedup
Full rebuild (baseline) 7:35 9:35 -27% (cache populating)
KiCad single file change 7:35 1:46 4.3x faster
wxWidgets single file change ~7:35 1:34 4.8x faster
No changes ~7:35 1:31 5x faster

Note: Asyncify post-processing takes ~1 min and runs every build. This is the irreducible minimum build time.